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Physical Habitat Conditions

3.0 PHYSICAL HABITAT CONDITIONS

3.1 HISTORICAL PHYSICAL CONDITIONS

3.1.1 HISTORICAL ANTHROPOGENIC DISTURBANCES

GOLD MINING

Hydraulic gold mining started in the mountains of the Yuba River Basin in 1853 and resulted in the release of vast amounts of sediment through the 1870s. Most of this sediment initially remained in the mountains, but by 1862, torrents of sediment were transported downslope to the valley and caused rapid aggradation and exacerbation of flooding along valley rivers (i.e., on the lower Yuba, Feather, Bear, American, and Sacramento rivers) (James and Singer 2008).

Sediment production in the region accelerated through the 1870s and by 1905, an estimated 1.4 billion cubic meters (m3) of hydraulic mining sediment had been produced in the Yuba, Bear, Feather, and American river basins (Table 3-1). While two major debris dams (i.e., Daguerre Point Dam in 1906 and Englebright Dam in 1941) were constructed on the Yuba River to prevent continuing movement of sediment into the Feather and Sacramento rivers, and ultimately the Bay-Delta, large amounts of low-lying, unconsolidated deposits reside downstream of all dams in each watershed, including the lower Yuba River, and are located largely between the modern levees that border the stream corridors. Thus, they are subject to erosion and transport down-valley.

Table 3-1. Sediment production from hydraulic mining in the Sierra Nevada (source: James et al. 2009).

Basin Volume (Million yd3) Relative Production (%)

Yuba River 684 49.0

Bear River 354 25.4

Feather River 100 7.2

American River 258 18.4

Total 1396 100

The immense residual deposit in the lower Yuba River, estimated by Gilbert (1917) at over 250 million m3 (327 million yds3) as of 1917, represented 24 percent of the hydraulic mining sediment produced in the region from 1853 to 1884 (James et al. 2009). Hydraulic mining sediment exacerbated flooding in the lower valleys and caused widespread impacts to farming and to navigation in the rivers. Disputes over the legality of hydraulic mining were largely resolved by a federal court in the Sawyer Decision of 1884 (Woodruff v. North Bloomfield Mining and Gravel Company), which enjoined hydraulic gold mining in tributaries to navigable rivers.Yuba Accord M&E Program 1 April 2013Draft Interim Report

http://en.wikipedia.org/wiki/North_Bloomfield_Mining_and_Gravel_Company

http://en.wikipedia.org/wiki/North_Bloomfield_Mining_and_Gravel_Company


The influx of mining debris into the Yuba River Basin dramatically altered the morphology of the lower Yuba River. Judge Lorenzo Sawyer recounted the following in his 1884 decision:

“Formerly, before hydraulic mining operations commenced, the Yuba River ran through this part of its course (from the foothills to Marysville) in a deep channel, with a gravelly bottom from 300 to 400 feet side on an average and with steep banks from 15 to 20 feet high, at low water, on either side. From the top of the banks, on each side, extended a strip of bottom-lands of rich, black alluvial soil, on an average a mile and a half wide, upon which were situated some of the finest farms, orchards, and vineyards in the state.”

With the onslaught of sand, gravel, and slickens from upstream, the lower 18 miles of the Yuba River were transformed into a braided, shifting stream system. The lower Yuba was, in 1900, described as “… one uninterrupted waste of sand and gravel” (Mansfield et al.. 1900). Any vestiges of the original channel were completely obliterated (Adler 1980). Figure 3-1 shows some of the impacts of the mining debris on the river channel in 1905.

Figure 3-1. The “Narrows” at Parks Bar on the Yuba River in 1905 (Source: Gilbert 1917).

By 1906, the supp1y of hydraulic mining debris from upstream areas was depleted and degradation became the dominant process along the Yuba River. The rate of erosional intensity was greatest between 1906 and 1912 and has since tapered off. It has been demonstrated that of Yuba Accord M&E Program 2 April 2013Draft Interim Report


the degradation that took place between 1912 and 1979, the majority occurred prior to 1940. By 1940, the Yuba River had scoured itself a single, stable channel (Adler 1980).

LEVEES, TRAINING WALLS AND DREDGINGConstruction of levees along the lower Yuba River to protect the town of Marysville started as early as 1868, and by the early 1960s, levees extended completely around the town of Marysville and approximately seven miles upstream along the north and south banks of the lower Yuba River. Additionally, commencing in 1880, a series of brush and debris dams was constructed on the lower Yuba River in an effort to control or store mining sediment loads in the basin. Early efforts consisting of brush dams were quickly overtopped, as was the concrete Barrier #1 that was located approximately 4 miles upstream of Daguerre Point Dam. Daguerre Point Dam was constructed in 1906, partially breached and repaired multiple times, most recently in 1963, and remains in place today.

Fifteen miles of 20-75 feet high cobb1e training walls were constructed between 1910 and 1935 by gold dredges to promote the scouring and formation of a permanent, stable channel (Adler 1980). The training walls extend along both banks of the lower Yuba River from a point located 4.5 miles upstream of Daguerre Point Dam to 2.5 miles downstream of the dam. The training walls encompass the entirety of the Dry Creek and Daguerre Point Dam reaches, and approximately half of the Parks Bar Reach. During the period of training wall construction and for up to 30 years following, gold dredges intermittently worked channel areas in these reaches, sometimes changing channel configuration and directly removing riparian vegetation (CALFED and YCWA 2005).

DAMS

During the late 1800s and early 1900s, development of the upper Yuba River watershed for hydropower and water supply was in progress. Most of the dams and diversions that were used primarily for gold mining were in place during this period, but they were being replaced or removed as developmental emphasis in the watershed shifted from gold mining to flood control, water supply and hydropower generation. Debris dams also were in place or being added at several locations throughout the middle to lower elevations of the watershed.

From the onset of industrial gold-mining and through the first half of the 1900s, several notable dams were constructed in the Yuba River Watershed, including Bowman Dam, Daguerre Point Dam, Spaulding Dam, Bullards Bar Dam, and Englebright Dam. Bowman Dam was constructed on Canyon Creek, a large tributary to the South Yuba River, in 1872. Originally constructed of rock fill 100 feet high, Bowman Dam was built by the North Bloomfield canal company to provide water supply for hydraulic mining. USACE’s Daguerre Point Dam was constructed in 1906 by the California Debris Commission and has been rebuilt several times in the same general vicinity since then (with no storage due to full sedimentation within a short time after construction). Spaulding Dam was constructed in 1913 on the South Yuba River. The original Bullards Bar Dam, a 175 foot-high dam creating 31,500 acre-ft of storage capacity, was Yuba Accord M&E Program 3 April 2013Draft Interim Report


constructed in the early 1920s at a location 2 miles upstream of the location of New Bullards Bar Dam (several successive brush, timber, and rock structures were constructed at Bullards Bar in the mid to late 1800s and subsequently destroyed by flood). USACE’s Englebright Dam, located about 23 miles northeast of Marysville, a 264 foot tall concrete dam with an original storage capacity of 70,000 acre-ft (and now reduced by about 17,500 acre-ft due to sedimentation) was constructed by the California Debris Commission (a unit of USACE) in the late 1930s and early 1940s, was completed in 1941, and is now owned by USACE.

3.1.2 FLOWS AND WATER TEMPERATURES

FLOWS

Numerous water storage, conveyance and diversion facilities constructed in the Yuba River Watershed have had varied effects on lower Yuba River flows. As early as the mid-1800s, when gold was first discovered and major construction activities associated with gold mining first took place, flows in the lower Yuba River were altered to meet a variety of water uses. Beginning during the last decade of the 19th century as hydraulic mining became less prominent, a combination of water supply, flood control and hydroelectric power generation became the dominant forces in altering flows in the watershed.

In addition to the series of dams previously mentioned, since the mid-1900s several additional dams, diversions and conveyance facilities have furthered altered flows in the Yuba River Watershed. Above 2,500 feet elevation in the watershed, diversion facilities belonging to South Feather Water & Power (SFWP) on Slate Creek, Nevada Irrigation District (NID) on the Middle and South Yuba rivers, and Pacific Gas & Electric Company (PG&E) on the South Yuba River and various tributaries divert substantial quantities of water from the upper Yuba River Basin.

In the lower Yuba River, the completion of Englebright Dam in 1941 played a substantial role in altering flows of the lower Yuba River during the summer and fall, primarily related to power generation at the Narrows 1 Powerhouse and operations for water supply for irrigation districts north of the Yuba River that hold water rights to the natural flow of the river. Additionally, the 175 foot-tall Bullards Bar Dam was originally constructed in the early 1920’s to regulate flows for power generation at the original Colgate Powerhouse. Construction of the Yuba River Development Project (YRDP), commencing operations in 1970, has altered the flow regime of the lower Yuba River below Englebright Dam due to its ability to store a relatively large amount of cold water higher in the system. Over the course of the 40-year period since the completion of the YRDP, the project has undergone large changes in operational practices and regulatory streamflow criteria. In recent decades, the use of Yuba River water, primarily through diversions at Daguerre Point Dam, increased with the expansion of irrigation systems within Yuba County.

The two primary gaging stations located at Marysville and Smartsville on the lower Yuba River have been in operation since before the YRDP was constructed. These gaging stations provide lower Yuba River hydrology for the pre-YRDP time period to compare to the hydrology since Yuba Accord M&E Program 4 April 2013Draft Interim Report


1970. From 1903 through 1943, USGS Gage 11419000 measured flows on the Yuba River near Smartsville, just below the mouth of Deer Creek. Since 1943, both the Smartsville Gage (USGS Gage Number 11418000), located at RM 22 (located above the confluence with Deer Creek) and the Marysville Gage (USGS Gage Number 11421000) at RM 6.2, have been in operation.

The following graphics demonstrate the total magnitude of hydrologic alterations in the Yuba River Basin. Figure 3-2 shows the calculated unimpaired flow for the North, Middle and South Yuba rivers based on gage data from WY 1976 through 2004 (compiled from NID, PG&E & YCWA relicensing studies). It is likely that flows similar to these have not been present in the Yuba River Basin since the late 1800s.

Figure 3-2. Calculated mean daily unimpaired flow (cfs) for the North, Middle and South Yuba rivers, WY 1976 - 2004.

By contrast, Figure 3-3 shows the historical daily flows for the same time period. These flows represent the current operational baseline in the Yuba River Basin, and are the context for the development and implementation of the Yuba Accord flow schedules. An expanded description of current facilities and operational criteria for the lower Yuba River is included in Attachment 1-A.

Yuba Accord M&E Program 5 April 2013Draft Interim Report


Figure 3-3. Mean daily historical flow (cfs) for the North, Middle and South Yuba rivers, WY 1976 - 2004.

Pre-YRDP flows at the Smartsville Gage were highly variable on a daily basis, and were generally low during the fall period. Figure 3-4 shows the mean daily flow (cfs) at the Smartsville Gage from July through October for the decade of 1950 to 1959, when pre-YRDP data were available. The pre-YRDP flows at the Marysville Gage were very low (as low as 20 cfs) during July through November in many years irrespective of water year type. Figure 3-5 shows the mean daily flow (cfs) at the Marysville Gage from July through October for the corresponding pre-YRDP decade of 1950 to 1959. Flows during the 1950s in September and October were below 50 cfs during many days of several years. Fall flow fluctuations commonly exceeded 50% with multiple phases within the season. Except in the driest of years, early summer flows exhibited a steady flow decline following peak spring runoff.



Figure 3-4. Mean daily flow (cfs) at the Smartsville Gage from July through October of 1950 to 1959.

Figure 3-5. Mean daily flow (cfs) at the Marysville Gage from July through October of 1950 to 1959.

WATER TEMPERATURES

Reservoir control gates at New Bullards Bar Dam have the ability to release water from two different reservoir storage elevations, thereby controlling the temperature of water released from the reservoir. In the years leading up to the Yuba Accord, YCWA used only the low-level outlet for water releases since 1993, pursuant to discussions with CDFG. Figure 3-6 shows the monthly average of daily mean water temperatures of the lower Yuba River, at the Marysville Gage, during the three periods for which water temperature data are available:



Pre-YRDP period from 1965 to 1968 (two wet and two below normal years1)

YRDP period from 1974 to 1977 (two wet and two critical years)

Modified operations during the YRDP period from 1993 to 20052 (five wet, four above normal, one below normal, one dry, and two critical water years)

The monthly average of daily mean water temperatures during the 1974 to 1977 period show reductions in summer water temperatures compared to the 1965 to 1968 period, even though the 1974 to 1977 period included the most severe drought (1976-1977) that the Yuba River Basin has experienced in recorded history. This shows the effect of YRDP operations on reducing summer water temperatures in the lower Yuba River.

Figure 3-6. Monthly average of daily Yuba River water temperatures at the Marysville Gage for periods of pre- and post-Yuba River Development Project.

Compared to the period of 1965 to 1968, the monthly averages of daily mean water temperatures were substantially lower during the 1993 to 2005 period, from mid-summer into the fall, with the average August temperature over 10 °F lower. The reduction in summer and fall water temperatures was greatly influenced by the continued releases of water from the coldwater pool in New Bullards Bar Reservoir, resulting from the modified operations in the YRDP.

3.1.3 HISTORICAL GEOMORPHOLOGY

1 Water year types are defined by the Yuba River Index (B-E, Yuba River Index: Water Year Classifications for Yuba River, 2000).2 Water temperature data are available for 1989 to 2005. However, after September 1993 and prior to implementation of the Yuba Accord, the low-level outlet of New Bullards Bar Reservoir was consistently used to release water for power generation at New Colgate Powerhouse to assist in the management of water temperatures in the lower Yuba River.Yuba Accord M&E Program 8 April 2013Draft Interim Report


In an effort to better understand the arc of mining debris impact and subsequent adjustment of the Yuba River, the RMT and YCWA undertook an effort to evaluate changes through time by utilizing historic maps and aerial photo sets of the Yuba River (see Technical Memorandum 1-2 in YCWA 2012).

A comprehensive catalog of aerial photos spanning the time period of 1936 through 2010 was compiled by L. Allan James for the RMT in 2010 and 2011 from sources including United States Geological Survey (USGS), USACE, California Department of Water Resources (DWR) and the California State Archives. YCWA (2012) used these photographs to evaluate historical channel and riparian (described below) changes in the lower Yuba River. Photo quality, reference datum, extent of coverage, and metadata varied widely across the various photo sets - as a result, only some of the years/photo sets were utilized for the historic comparison. The photo sets utilized in this analysis described below were reasonably comparable, spanned the period from prior to the construction of Englebright Dam, through the construction of the YRDP facilities, and extend to the modern day. Additionally, the selected photo sets span several very large channel changing flood events.

CHANNEL CHANGE THROUGH TIMEBecause no channel measurements exist that correspond with the aerial photo sets, any quantitative analyses of the historical morphology would introduce too many inaccuracies or involve too many assumptions to provide any meaningful comparisons through time. While the flow widths and wetted areas can be estimated from the aerial photos, they do not represent the same discharge. They also do not even represent the same underlying channel morphology, as intervening flows between the aerial photo dates have likely altered the channel bed with erosion and deposition patterns that are impossible to determine. Therefore, even if two aerial photos show the same discharge, any differences in the observable morphologies would be overly difficult to contextualize.

Nonetheless, review of aerial photographs taken over time has provided some qualitative views and representation of changes that have occurred in the lower Yuba River channel over the past. The figures and discussion below represent simple examples of the type of demonstrated changes in the channel that have occurred.

Between 1947 and 1970, the lower Yuba River within the Dry Creek study site experienced dramatic changes to the channel location and morphology, partly due to anthropogenic activities (Figure 3-7). The 1947 photo shows dredger mining operations on the north and south side of the valley, and the river flowing as a single-thread channel. By 1970, the mining operations on the north side had ceased and the south side operations had expanded northward into the valley, thus forcing the channel farther north as well. Also by 1970, the channel has switched from a single-thread stream to a multi-thread or braided stream. The current channel is less braided than in 1970, but still exhibits flow splits and backwater regions at this site. From a geomorphic perspective, a change from single-thread to multi-thread channels generally means an increase in Yuba Accord M&E Program 9 April 2013Draft Interim Report


sediment load and thus a decrease in stability. By distributing the flow among several pathways, the overall width-depth ratio also generally increases.

The Daguerre Point Dam site also underwent a large geomorphic change during this time period (Figure 3-8). The 1947 photograph shows two large, parallel channels through this reach, while the 1970 photograph shows that the perennial, fully connected, within-bank low flows had been abandoned within the northern channel. By 1970, low flow had become concentrated in the southern channel. Recent field reconnaissance reveals that the river has built up a natural levee at the upstream entrance to this northern channel, perhaps due to the increased sediment input from upstream. Subsequently, this abandoned northern channel is not re-inhabited by perennial low flow, but it has always exhibited several perennially wet sections. Results from 2D hydrodynamic models that are based on 2008 topography show that currently this natural levee breaches and the northern channel inundates when the flow exceeds ~ 10,000 to 15,000 cfs (G. Pasternack, pers. comm. 2012). From a geomorphic perspective, the increased flow concentration in the south channel would be expected to be matched by either an increase in channel width and/or depth, or (if little to no changes in the geometry occurs) an increase in the frequency of flows spilling out of the channel banks onto the floodplain. The analyses of riparian vegetation in the following section were based on a buffered zone around the low-flow channels. Therefore, the conceptual “loss” of the northern perennially active channel resulted in the apparent majority of the loss of riparian vegetation seen at this site, even though there was little to no actual change in the vegetation in either channel. The photos show that the stability of the ponds in the former pools in the abandoned northern channel maintained and perhaps actually promoted establishment of vegetation along the wetted perimeter.

3.1.4 HISTORICAL VEGETATION

AERIAL PHOTOGRAPH ANALYSIS

YCWA (2012) conducted a historical aerial photograph analysis to describe changes over time to total vegetation delineated within the valley walls, riparian vegetation delineated within 50 ft of the active river channel,3 and channel alignment (see Technical Memorandum 6-2 in YCWA 2012). YCWA included qualitative descriptions of current conditions observed during field surveys conducted in 2012, as well as hydrologic conditions across the period of record where they contribute to understanding of changes over time. In general, YCWA used quantitative data for changes in vegetation to frame the qualitative analysis. A more detailed discussion is provided in YCWA (2012). In order to capture changes over time within each of the eight reaches, a total of eight study sites was established, with one study site within each reach (for more information on reach delineations, see YCWA 2012). The lengths of these sites were established at approximately 20 times bankfull width and extended laterally across the valley breadth. The downstream start point of each site was chosen using a random number generator.

3 Total vegetation is inclusive of riparian vegetation.Yuba Accord M&E Program 10 April 2013Draft Interim Report


Figure 3-7. Yuba River in the vicinity of the Dry Creek Reach in 1947 and 1970.



Figure 3-8. Yuba River in the vicinity of the Daguerre Point Dam Reach in 1947 and 1970.



CHANGES IN AREAS OF TOTAL VEGETATIVE COVER AND RIPARIAN VEGETATION COVER To determine the cumulative change over time4 in total vegetative cover and riparian vegetation cover for the Marysville, Timbuctoo Bend, Narrows, and Englebright Dam study sites, YCWA compared the aerial photographs from 1937 and 2010. Due to the availability of aerial photographs, the time sequences associated with each study site was somewhat variable, as indicated in Table 3-2. Cumulative changes in total vegetative cover over time are summarized in Table 3-2, and Figure 3-9 summarizes the trends associated with the changes in total vegetative cover. Table 3-3 summarizes cumulative changes in riparian vegetative cover and Figure 3-10 summarizes the trends associated with the changes in riparian cover. Because the vegetation studies were only done at the site scale, the values in Tables 3-2, 3-3 and Figures 3-9, 3-10 do not represent the comprehensive changes in each reach (nor therefore for the full segment). Instead, they are only meant to be indicative of the trends in changes to the vegetative cover that occurred along the lower Yuba River.

Table 3-2. Changes in total vegetative cover (measured in ft2 per year).

Site 1937 to 1947 1947 to 1970 1970 to 1987 1987 to 2010 Total*

Englebright -35,086 -- -1,820 ** 10,221 -2,583

Narrows -10,316 -- 3,891 ** -6,286 -1,262

Timbuctoo -119,037 55,895 -62,979 56,789 4,531

Parks Bar -- 35,105 16,326 8,560 20,347

Dry Creek -- -109,963 -40,958 98,375 -15,282

DPD -- -71,521 208,921 -42,285 14,827

Hallwood -- 46,631 10,275 38,197 33,742

Marysville -13,205 5,374 19,019 -784 4,066* The time range for the Englebright, Narrows, Timbuctoo, and Marysville sites span from 1937 to 2010. The other sites span from 1947 to 2010.** These values represent the change between 1947 to 1987, because no 1970 data exist.

Cumulative changes in vegetative cover in the Englebright Dam and Narrows study sites decreased. For the remaining study sites, including Marysville, Hallwood, Daguerre Point Dam, Dry Creek, Parks Bar, and Timbuctoo Bend study sites, the cumulative change in vegetative cover increased. The least amount of vegetation change over time was observed in the Englebright Dam, Narrows and Marysville sites. The Dry Creek, Daguerre Point Dam and Hallwood sites had the greatest vegetated area, and YCWA identified those sites as the most dynamic (i.e., both decreased in vegetative cover through 1970 and then increased through 2010).

4 Cumulative change describes the changes to observable area for either total vegetation or riparian vegetation from the earliest photo date to the most recent photo date.



Figure 3-9. Trends in total vegetative cover (i.e., vegetation within the delineated river valley) over time.

Table 3-3. Changes in riparian vegetation cover (measured as ft2 per year).

Site 1937 to 1947 1947 to 1970 1970 to 1987 1987 to 2010 Total*

Englebright -16,035 -- -146 ** 1,937 -1,666

Narrows -9,052 -- 2,430 ** -4,231 -1,241

Timbuctoo -20,685 2,178 8,632 2,971 799

Parks Bar -- 4,821 15,183 3,471 7,124

Dry Creek -- 20,573 -18,601 16,880 8,654

DPD -- -19,484 5,153 18,840 1,155

Hallwood -- -1,017 7,578 8,747 4,867

Marysville -304 -560 3,635 3,364 1,688* The time range for the Englebright, Narrows, Timbuctoo, and Marysville sites span from 1937 to 2010. The other sites span from 1947 to 2010.** These values represent the change between 1947 to 1987, because no 1970 data exist.



Figure 3-10. Trends in riparian vegetation cover (i.e., vegetation delineated within 50 ft of the active channel) over time.

Cumulative changes in riparian vegetation cover in the Englebright Dam and Narrows study sites decreased with very little detectable change for the Narrows study site. For the remaining study sites, the cumulative change in riparian vegetation cover increased. The observed changes for the Englebright Dam, Narrows and Marysville study sites were very small. For the Dry Creek and Parks Bar study sites, the greatest changes were observed, with dramatic increases in riparian vegetation cover. The magnitude of change of riparian vegetation between photoset years (in a stepwise comparison) was greater than that seen in the cumulative riparian vegetation cover change.

3.2 CURRENT PHYSICAL HABITAT CONDITIONS

3.2.1 SPATIAL STRUCTURE / GEOMORPHOLOGYGeomorphology is the study of the landforms on the surface of the Earth. Geomorphic analysis involves mapping the shape of landforms to describe their spatial patterns, observing landforms over time to record their changes, exploring the drivers and mechanisms of landform change, and evaluating the responses of biological, chemical, and hydrological processes to geomorphic change. Beyond understanding natural conditions and dynamics, geomorphology is essential in Yuba Accord M&E Program 15 April 2013Draft Interim Report


planning societal use of the landscape and in figuring out the impacts of societal activity on the environment and through it the externalities that come back and harm society and economics. The RMT has been conducting applied research to understand the fluvial geomorphology of the lower Yuba River downstream of Englebright Dam. There are three major components of this section:

Characterizing and analyzing the landforms in the river corridor at three spatial scales: segment (~103-104 W), reach (~102-103 W), and morphologic unit (~1-10 W), where W is channel width.

Relating reported and observed characteristics of the primary salmonid lifestages to the abundance and diversity of the landforms.

Characterizing and analyzing the changes in landforms over a 7-9 year period.

MACRO-HABITAT ANALYSIS

The procedure used in morphologic analysis involved four phases: topographic mapping, 2D hydrodynamic modeling, classification of hydraulic and topographic patterns, and analysis of resulting landform types at all three scales. A combination of ground-based surveying, boat-based bathymetry, and airborne LiDAR was used to construct a river-corridor digital elevation model (DEM), excluding the inaccessible Narrows Reach. The freeware hydrodynamic modeling program SRH-2D v.2.1 (Yong Lai, U.S. Bureau of Reclamation, Denver, CO) was then used to model the spatial pattern of water surface elevation, depth, velocity, and other derivable variables for the entire mapped river at discharges ranging from very low flows (300 cfs) to valley-filling floods (110,400 cfs). Some relevant discharges for mapping fluvial landforms included a representative base flow (880 cfs above Daguerre Point Dam and 530 cfs below it), a representative bankfull flow recognizing that channel capacity actually varies down the river (5000 cfs), and representative floodplain-filling flow (21,100 cfs). A full report on the landforms and their organization is available in Wyrick and Pasternack (2012).

To understand the temporal changes in the channel landforms, two digital topographic maps were subtracted from each other. The initial map was created by the US Army Corps of Engineers in 1999 between the Narrows Pool and the Feather River, and is presented in the form of 2-ft contours. The second map was created through a phased effort between 2006 and 2009. Timbuctoo Bend (between Blue Point Mine and Highway 20) was mapped during the dry season of 2006, using a combination of ground-based total station surveying and boat-based bathymetry. The remaining downstream sections of the lower Yuba River were mapped by LiDAR in September 2008, with some ground-based surveying and boat-based bathymetry conducted between 2008 and 2009 to fill in the data gaps. The epochs used for differencing are therefore seven years for Timbuctoo Bend (1999-2006) and nine years for the rest of the lower Yuba River (1999-2008). There were no maps made upstream of Timbuctoo Bend during the 1999 surveys, therefore those sections will be excluded from the channel change discussion and analyses. The survey data were converted into DEM (digital elevation model) rasters in ArcGIS and subtracted to create a Difference of DEMs (DoD) raster. Managing the uncertainties involved with comparing topographies mapped with different methods, and other details of the mapping Yuba Accord M&E Program 16 April 2013Draft Interim Report


procedure, are presented more robustly in Carley et al. (2012).

SEGMENT SCALE EVALUATION

Segment Scale CharacteristicsThe downstream boundary of the river segment is the confluence with the Feather River, and the upstream boundary is the Englebright Dam. The total segment length is ~25.2 mi measured along the baseflow thalweg (23.0 mi measured along the valley centerline). Riverbed thalweg elevations range from ~30-290 ft above mean sea level (Figure 3-11). The average bed channel slope of the thalweg from the upstream end of Timbuctoo Bend (downstream extent of The Narrows) to the confluence with the Feather River is 0.16%, while the average bed channel slope between Deer Creek and Englebright Dam is 0.31%. Primary tributaries are Deer Creek (RM 24.5) and Dry Creek (RM 14.4). Daguerre Point Dam is a 26-ft high debris barrier structure located at RM 12.0 that creates a slope break and partial sediment barrier (Figure 3-11), which also creates hydraulic head utilized for irrigation diversions.

The river corridor is confined in a steep-walled bedrock canyon for the upper ~2.0 RM, then transitions first into a wider bedrock valley with some meandering through Timbuctoo Bend, then into a wide, alluvial valley from ~RM 19.3 to the mouth. The river has a history of hydraulic mining that is the source for much of the present alluvium. Tailings that remain from the hydraulic mining were used to create training berms in some sections of the corridor. Hyporheic seeps have been noted in areas of the mined alluvium.

Inundation ZonesThe Lower Yuba River study segment has a wetted area of 510 acres and average wetted width of 195 ft at baseflow conditions (880/530 cfs above/below DPD). At near-bankfull flow conditions (5,000 cfs) the wetted area increases to 829 acres and the wetted width to 319 ft (Table 3-4), both increases of ~ 63%. During flood conditions (21,100 cfs) the wetted area increases to 1703 acres and the wetted width to 654 ft, both increases of over 100% as compared to the bankfull values.

Floodplain ConnectionA flood-frequency analysis of the annual peak discharges recorded at the USGS stream gage near Marysville (#11421000) provides average annual return periods of 1.25 years and 2.5 years for the bankfull and flood discharges, respectively. Bankfull flows for similar rivers are generally assumed to occur with return periods of 1.5-2 years. The fact that the lower Yuba River is less than this implies that the channel is naturally undersized relative to generalized expectations and flows spill into the floodplain at a more frequent rate.



Figure 3-11. Longitudinal thalweg profile showing reach breaks.

Table 3-4. Wetted channel area and width as a function of discharge.Discharge (cfs) Wetted Area (ac) Average Width (ft)

Baseflow - 880/530 510 195

Bankfull - 5,000 829 319

Flood - 21,100 1703 654

The total area of the geomorphically-active channel corridor was manually drawn in ArcGIS, and encompasses a segment-scale area of 2,645 acres. With this, the inundation areas in Table 3-5 provide another view of how connected the channel is to the floodplains. When a bankfull flow occurs, it fills about 20% of the valley corridor area. A flood flow fills about 2/3 of the valley corridor. Combining this with the return intervals for the flows, this analysis suggests that 2/3 of the full valley becomes inundated on average about once every 2.5 years, and thus the floodplains are considered hydraulically well-connected to the channel.

The hydraulic analyses show that the channel is well-connected to the floodplains, but not why. There are two major characteristics of the lower Yuba River that can explain its well-connectedness. First, the valley consists of unconsolidated, large sediment that exhibit low bank stability and is continually re-worked by diverse geomorphic processes. Second, because the channel is undersized, the flood flows and their associated scour potential are generally relocated outside of the channel and onto the floodplains.



Channel ClassificationStream classification is a hierarchical inventory system that objectively describes a channel “so that consistent, reproducible descriptions and assessments of condition and potential can be developed” (Rosgen 1994). By classifying the lower Yuba River, a clear baseline is established as to what types of rivers the lower Yuba River should be compared with, as either a possibly degraded or pristine reference system. The Rosgen Stream Type classification (Rosgen 1994) is a common method because it incorporates physical characteristics of the channel that are objectively determined. Using this metric, the lower Yuba River is classified as a C3 stream type (Table 3-5), identifying it as being a “slightly entrenched, meandering, riffle/pool, cobble-dominated channel with a well-developed floodplain” (Rosgen 1994). More discussion of channel entrenchment and its implication is provided in the next section.

Table 3-5. Hierarchical classification of the lower Yuba River based on Rosgen (1994) stream types.Channel Characteristic lower Yuba River Value Classification

# of Threads 1 Single

Entrenchment Ratio 2.7 Slightly Entrenched

Width/Depth Ratio 80 Very High

Sinuosity 1.1 Low to Moderate

Slope 0.0016 Moderate

Mean Substrate Size (mm) 102.6 Small Cobble

Rosgen Stream Type C3

REACH SCALE EVALUATION

Reach DelineationsAt the geomorphological reach scale, eight distinct reaches were delineated and characterized for the lower Yuba River. The key geomorphic indicators of reach breaks were presence of tributary confluences, presence of dams, and substantive changes in valley width, riverbed slope breaks, and substrate. From upstream to downstream the reaches are named Englebright Dam, Narrows, Timbuctoo Bend, Parks Bar, Dry Creek, Daguerre Point Dam, Hallwood, and Marysville reaches (Figure 3-11). Tributary junctions form the upstream boundary of two reaches (Narrows and Dry Creek) and dams bound two more reaches (Englebright and Daguerre Point Dam). The other reach boundaries are formed by hydro-geomorphic variables: onset of emergent floodplain gravel (Timbuctoo Bend); transition from confined bedrock valley to wider, meandering system (Parks Bar); and decreases in bed channel slope (Hallwood and Marysville) (Table 3-6).

Reach CharacteristicsTo investigate the differences in discharge-width relationships between the reaches at the key inundation levels, model-predicted wetted area polygons for baseflow, bankfull, and floodway Yuba Accord M&E Program 19 April 2013Draft Interim Report


were used. Calculations were made for the widths at each cross-section (spaced every 20 ft streamwide) for each relevant flow regime (Figure 3-12), as well as for the average widths per reach (Table 3-7). Between baseflow width and near-bankfull width, the Marysville and Timbuctoo Bend Reaches experience the smallest increase in flow width of ~33%. The Daguerre Point Dam Reach, on the other hand, almost doubles in width between baseflow and bankfull, and also experiences the greatest overall increase in width as the floodway is ~ 5.2 times as wide as the baseflow wetted area, which benefits from the overflow filling of an adjacent channel just downstream of Daguerre Point Dam. The Englebright Reach is the most confined as its canyon width is only ~2 times wider than the baseflow width, although the ratio for both the Marysville and Timbuctoo reaches are only slightly larger. The Narrows Reach is likely more confined than the rest of the segment, but we do not have model results with which to compare.

Table 3-6. Newly proposed reaches of the Lower Yuba River with geomorphic delineations.

Reach NameValley Width (ft)

Bed Slope (%)Thalweg

Length (ft)Starting Point

DescriptionMin Mean Max

Englebright Dam

316 415 693 0.31 4,130 Englebright Dam

Narrows 162 304 596 n/a 6,700Confluence with Deer

Creek

Timbuctoo Bend

373 589 1866 0.201 20,790

Onset of emergent gravel floodplain

upstream of Blue Point Mine

Parks Bar 387 1007 1432 0.188 25,980Channel widening near

Highway 20 Bridge

Dry Creek 783 987 1552 0.135 12,470Confluence with Dry

Creek

DPD 755 1628 2305 0.176 18,500 Daguerre Point Dam

Hallwood 573 1175 2394 0.131 27,500Slope break near Eddie

Drive

Marysville 325 744 1842 0.052 17,500Slope break; No evident feature



Figure 3-12. Variability of wetted area and corridor widths at the segment and reach scales for baseflow (green line), bankfull (red), and flood conditions (blue).

Table 3-7. Average widths per reach as a function of discharge.Reach Baseflow* Width (ft) Bankfull Width (ft) Floodway Width (ft)

Englebright Dam 120 169 237

Narrows -n/a- -n/a- -n/a-

Timbuctoo Bend 205 277 441

Parks Bar 199 316 678

Dry Creek 248 427 865

Daguerre Point Dam 197 393 1028

Hallwood 183 335 692

Marysville 174 231 379

*Baseflow is a paired discharge of 880 cfs above DPD and 530 cfs below; Bankfull = 5,000 cfs; Floodway = 21,100 cfs.



Entrenchment is a description of the vertical containment of the river channel, and is quantitatively expressed as a ratio of the flood-prone width to the bankfull width. The smaller this ratio is (i.e., the closer the two widths are to each other), the more entrenched the channel is. The average entrenchment ratio (ER) for the segment scale has been previously shown, which indicates that the channel, on the whole, has a well-developed floodplain. However, there are variations at the reach and cross-sectional scales that indicate there are some short stretches of the lower Yuba River that are entrenched (Figure 3-13). Entrenched sections do exist within the Marysville and Hallwood reaches; however, these reaches also exhibit some of least entrenched sections (highest ratio). Most of the reaches are classified as “slightly entrenched” or “not entrenched” (ER > 2.2), similar to the segment scale. Timbuctoo and Englebright, however, are classified as “moderately entrenched” on average (1.4 < ER < 2.2). All of reaches exhibit some entrenched sections (ER < 1.4), although they all also exhibit more sections that have ratios greater than 2.2 (slightly to not entrenched). Thus, the spatial scale used to analyze and characterize a river is important.

Figure 3-13. Variability of entrenchment ratios among all cross-sections of the lower Yuba River. The orange and green lines represent the segment and reach averages, respectively. An entrenched section exhibits a ratio < 1.4 and a moderately entrenched section exhibits 1.4 < ER < 2.2. Sections with ratios greater than 2.2 are considered slightly or not entrenched.



MORPHOLOGICAL UNIT SCALE EVALUATION

Morphological Unit Definition and DelineationA morphological unit (MU) is defined as a discernible topographic landform within the channel and floodplain that represents a distinct form-process association, and whose size is typically at the length scale equivalent of 1-10 channel widths (but can be smaller). It is important to note that a MU is not a habitat definition, and therefore not dependent on stage or discharge, but rather a classification of the landforms that create the environmental requirements of a biologic community. The “mesohabitat” reflects aquatic habitat conditions based on combinations of hydraulic and biologic conditions, and are therefore largely dependent on stage and discharge. Using 2D model results, four suites of MU types that are discretely bounded by inundation levels were delineated within the lower Yuba River segment. Applying numerical thresholds to the baseflow depth and velocity, eight in-channel bed MUs were automatically and objectively delineated: pool, run, chute, riffle, riffle transition, fast glide, slow glide, and slackwater. Outside the baseflow wetted area, other fluvio-geomorphic data, such as topography, DEM difference maps, and conveyance (i.e., depth times velocity) rasters, were used to help hand-delineate bankfull, floodway, and valley MU types. The wetted area between the baseflow and bankfull discharges bounds the in-channel lateral bar, medial bar, point bar, and swale units. The wetted area between bankfull and floodway bounds the floodplain, flood runner, island-floodplain and mining pit units. Terrace, high floodplain, island high floodplain, and levee units are only delineated outside of the floodway wetted area. In total, 31 MU types were delineated, with the others occasionally transcending between the inundation region boundaries. Refer to Wyrick and Pasternack (2012) for further definitions of each particular MU type.

Morphological Unit AbundancesStatistical abundances were calculated for each MU type across the relevant discharge regimes. At baseflow, the most abundant MU is slackwater at the segment scale, while pool, fast glide, riffle, and riffle transition dominated at the reach scale (Table 3-8). At bankfull flow, the most abundant MU at the segment scale is lateral bar, with pool still dominating in the highly constricted upper and lower reaches. Within the floodway boundary, the floodplain is the most abundant segment-scale MU and within the mid-segment reaches, but pool is still the most abundant in the highly constricted upper and lower reaches. Outside of the floodway zone, terrace is the most abundant unit at the segment scale, as well as all of the reaches except for Englebright, where hillside/bedrock dominates. The inequality of abundances and absences among the MUs at all discharges is one indicator that channel morphology is non-random in its spatial structure.



Table 3-8. Percentages of most abundant in-channel bed morphological units per reach.Reach Most Abundant MU MU Area

(% of baseflow wetted area)

Englebright Pool 41

Timbuctoo Pool 20

Parks Bar Riffle 19

Dry Creek Fast Glide &

Slackwater*

18

DPD Riffle Transition 28

Hallwood Fast Glide 20

Marysville Pool 52

Total lower Yuba River Slackwater 16

*Fast Glide and Slackwater are equally abundant in area

Morphological Unit OrganizationTo further explore the question of random organization among the MUs, the in-channel baseflow units were analyzed with respect to the longitudinal distribution of each unit and adjacency probabilities between sets of units. If the lower Yuba River were randomly organized, then it would exhibit a uniform longitudinal distribution for all units, with equal probabilities of being located adjacent to any other unit type. The results from our analyses show that the lower Yuba River is not randomly organized (i.e., units exhibit spatial ‘preference’ and ‘avoidance’ for locations along the longitudinal profile) (Figure 3-14) and with respect to being next to each other. At the segment scale, chutes and runs are more predominant in the upper reaches of the lower Yuba River. Pools are unequally distributed with the highest abundance between the upper and lower reaches and lower abundance in the middle reaches, except for the large scour pool downstream of Daguerre Point Dam. Riffles exhibit uniform probabilities through most of the reaches, except for Englebright and Marysville. Riffle transitions trend generally upwards in occurrence probability from the Englebright to the DPD Reach, peaking in the Hallwood Reach, and then drastically declining into the Marysville Reach. Slackwater and slow glide units, however, are distributed fairly uniform across the segment. Results from the adjacency analyses show that there is a strong organizational structure evident in the adjacency probabilities (Table 3-9). Within the baseflow inundation region, a majority of the in-channel bed units exhibit higher than random (> 12.5%) adjacencies to riffle transition and slow glide. Each unit exhibited a much higher than random preference towards at least two other units, while also exhibiting a much higher than random avoidance (< 12.5%) to others.



Figure 3-14. Cumulative distribution functions for areas of in-channel bed MUs. Vertical dotted lines represent reach breaks. Diagonal dash-dot line represents uniform distribution.

Table 3-9. Percent of unit types adjacent to starting unit (left column) for all in-channel bed MU polygons. Green highlighted boxes represent greater-than-random preference probabilities (>> 12.5%); Yellow boxes represent near-random adjacency probabilities (~12.5%); Pink boxes represent greater-than-random avoidances (<< 12.5%).

Starting UnitChute

Fast Glide

Pool RiffleRiffle

TransitionRun

Slack-Water

Slow Glide

Chute 0.0% 6.0% 1.3% 34.9% 6.9% 48.4% 0.5% 2.0%

Fast Glide 0.6% 0.0% 8.3% 5.9% 39.5% 8.5% 8.3% 28.9%

Pool 0.6% 34.9% 0.0% 0.1% 3.6% 7.0% 14.6% 39.2%

Riffle 5.5% 5.4% 0.0% 0.0% 39.2% 11.9% 13.3% 24.6%

Riffle Transition 0.2% 8.6% 0.3% 6.0% 0.0% 2.4% 37.1% 45.5%

Run 6.7% 31.0% 7.4% 28.9% 20.6% 0.0% 1.2% 4.2%

Slackwater 0.1% 3.0% 1.3% 2.1% 23.7% 0.3% 0.0% 69.5%

Slow Glide 0.1% 7.4% 1.6% 2.6% 25.9% 0.8% 61.6% 0.0%



The spatial organization of the MUs was also analyzed with respect to the longitudinal spacing between like units and the lateral variability of units across the channel width. Classic research states that some morphological units, such as pools and riffles, tend to be spaced about 5-7 channel widths (W) downstream from each other. The key finding of this analysis is that none of the morphological units exhibit the traditional 5-7 W spacing at the segment scale, with spacing between in-channel units ranging from 2.7–4.4 W (Table 3-10). Given the high resolution of the topographic map, long segment size, and objective delineation of MUs, it is not surprising that the results deviated from classic studies. Some of the units, however, do exhibit the classic spacing metric at the reach scale, such as bedrock/boulder riffles in Englebright Dam Reach (6.4W) and pools in Parks Bar Reach (5.3W).

Table 3-10. Mean longitudinal spacing of morphological units by absolute distance (ft) and normalized distance (channel widths) at the segment scale.

ChuteFast glide

Pool RiffleRiffle

Trans.Run Point bar Swale

Distance (ft) 1,390 959 1,365 1,059 1,014 840 3,651 2,423

# widths 4.4 3.1 4.4 3.4 3.2 2.7 11.7 7.7

# of spacings 82 121 91 106 111 139 30 36

To determine whether the lower Yuba River exhibits significant lateral variability, the number of MUs at each cross-section were counted and compared. At the segment scale, the bankfull lower Yuba River exhibits an average of 8.8 MUs per cross-section. At the reach scale, the variability was normalized by the average reach width in order to remove the possibility that wide channel sections have more spatial availability for more MUs than narrow channel sections (Figure 3-15). At the normalized reach scale, the Englebright Dam and Marysville reaches exhibit the highest lateral complexity of about 12 MUs, while the Daguerre Point Dam reach exhibits the lowest complexity of about 7.5 MUs per cross-section. Overall, these results demonstrate that the lower Yuba River exhibits significant longitudinal and lateral landform heterogeneity.

FISHERIES PHYSICAL HABITAT

Channel Complexity and Habitat DiversityThe previous discussions highlight the complexity of the channel geomorphology. Within the bankfull channel, there can be between 2 and 22 distinct MUs at any given cross-section, with an average of almost 9 units. Thus, any given cross-section is not associated with any one MU or any one combination of hydraulics, and therefore not any one habitat. There exists a complex and diverse suite of potential habitat at any given location. For example, one cross-section might have (from bank to bank) a swale, lateral bar, slow glide, medial bar, riffle transition, riffle, pool, and point bar. That illustrates how there can be 8 MUs across one cross-section.



Figure 3-15. Lateral variability within the bankfull inundation region of morphological units normalized by the ratio of average reach width to local cross-sectional width. Green lines represent reach-scale averages and vertical dashed lines represent reach breaks.

At the broader scale of the lower Yuba River segment, the channel complexity is highlighted by the diversity of MU types and their varying distributions within the valley. The complexity in the landforms creates diversity in the flow hydraulics. It is important to note here that this geomorphic analysis can only interpret the depth and velocity influences on fishery habitat, and therefore excludes any correlation with other habitat factors, such as temperature, turbidity, overhanging cover and submerged cover.

Salmonid Spawning Substrate Suitability and AvailabilityThe overall mean substrate diameter (Dmean) within the bankfull channel is 97.4 mm. On the lower Yuba River salmonids tend to spawn in mean substrate sizes ranging from about 50-150 mm. The average Dmean at each cross-section was calculated and plotted as a longitudinal distribution (Figure 3-16). This analysis shows that most of the channel is characterized by average Dmean values within the acceptable spawning substrate size. The exceptions are sand/silt areas near the confluence of the Feather River and the boulder/bedrock regions in the upper sections of Timbuctoo Bend and most of Englebright Dam reaches.



Figure 3-16. Longitudinal distribution of the mean substrate diameter. The box represents the typical range of spawning substrate sizes observed on the lower Yuba River.

Morphological Unit Availability and Diversity at Baseflow for Salmonid Lifestages

Each lifestage is usually associated with a preferred combination of depth and velocity (often termed “meso habitat”), and the MUs that best exhibit these hydraulic combinations at baseflow were identified for this analysis (Table 3-11). This does not mean that these lifestages can only exist within those hydraulic combinations, and therefore not only within those MUs. Therefore, the areas shown in Table 3-8 should be considered as conservative, minimum values. Nevertheless, these numbers show that there is substantial area of habitat at base flow for the three main salmonid freshwater lifestages. Note that the embryo incubation lifestage has the same MU need as the spawning lifestage. Also note, once again, that this geomorphic analysis can only interpret the depth and velocity influences on fishery habitat, and therefore excludes any correlation with other habitat factors, such as temperature, turbidity, overhanging cover and submerged cover.

Table 3-11. Array of MUs that provide some minimum percent of potential areas for salmonid lifestages.

Reach

Adult Holding Spawning Juvenile Rearing

Pool MUs Riffle, Run, Riffle Transition MUs

Slow Glide, Slackwater MUs

Percent Areas of Baseflow ChannelEnglebright 52 9 32Timbuctoo 9 37 32Parks Bar 5 48 27Dry Creek 7 36 34

DPD 8 48 22Hallwood 20 38 25Marysville 41 19 28

Total lower Yuba River 16 37 28



FLUVIAL GEOMORPHIC PROCESSES

Sediment BudgetDifferencing the 1999 and 2006-2008 DEMs gives a net change in topographic depth at each raster pixel. Multiplying the net depth change at each pixel by the pixel size (5ft by 5ft) gives a net volume change at each pixel. These pixel-sized volumes can then be summed within any boundary of interest. The total volume displaced was over 175 million cubic feet, with a net export volume of ~22.4 million cubic feet. However, this volume represents different time epochs since Timbuctoo Bend was surveyed in 2006 and the rest of the lower Yuba River in 2008. A more appropriate view of the sediment budget would therefore be to annualize the volumes. The total volumes were divided by the time epochs (7 years for Timbuctoo and 9 years for the rest of the lower Yuba River), then summed to determine the net annual sediment volume change for the segment and reach scales (Table 3-12). In total, the lower Yuba River is exporting about 0.6 million cubic feet of sediment per year to the Feather River. At the reach scale, the Timbuctoo Bend and Dry Creek reaches are net erosional, while the others are net depositional.

In general, more scour has occurred upstream of the Daguerre Point Dam than downstream. The longitudinal pattern of net changes in depth averaged across the valley cross-sections (Figure 3-17) indicates a downstream to upstream temporal sequence of erosion since the installment of Englebright Dam (Carley et al. 2012).

Table 3-12. Segment and reach scale comparisons of net annual sediment volume changes.Reach Net Annual Sediment Volume Change (M ft3/year)

Timbuctoo Bend -1.58

Parks Bar 0.10

Dry Creek -2.02

Daguerre Point Dam 1.58

Hallwood 1.30

Marysville 0.03

Lower Yuba River Segment -0.60



Figure 3-17. Longitudinal profile of mean vertical change (1999-2008) within valley-wide, 20-ft long, cross-sectional intervals. The dashed line represents the average value for the three statistically different regions of Below DPD (green), Above DPD (orange), and Timbuctoo Bend (blue).

The DoD represents sediment changes between 1999 and 2006-2008, and the MU map was created based on the 2006-2008 topography. Therefore, an analysis of the sediment changes at the MU scale does not necessarily represent the processes occurring at this scale. Instead it represents the changes that occurred to create the MU landforms. Table 3-13 lists some of the major MUs and their associated net volumetric changes. These budgets are listed as volumes rather than annual rates because the time incongruity between the topographic change and MU maps. Therefore, they should be read as ‘sediment changes that occurred in the creation of each MU, not as sediment changes occurring within each MU.

Table 3-13 shows that ~99% of the total displaced sediment volume for pools was scoured away. This means that 99% of the sediment volumes in the areas that are now pools were displaced by scour processes. Additionally, the areas that ended up as riffles experience ~18% deposition, which indicates that they appear to be rejuvenated relative to the areas that ended up as pools. This constitutes “self-maintenance” of riffle-pool relief, which is a key performance indicator in the M&E Plan.



Table 3-13. Total scour, fill, and net volumetric changes that occurred to create each MU, ordered from most net fill to most net scour. Note: not all MUs are listed.

Morphological Unit Fill Total (ft3) Scour Total (ft3) Net (ft3)

Floodplain 29,863,418 -13,259,171 16,604,247

Terrace 10,080,282 -5,091,391 4,988,891

Point Bar 3,954,894 -375,467 3,579,427

Medial Bar 2,152,193 -1,288,052 864,141

Swale 2,785,319 -2,582,373 202,946

Cutbank 10,131 -594,893 -584,762

Riffle Transition 1,279,960 -3,350,052 -2,070,092

Slow Glide 695,764 -3,075,224 -2,379,461

Chute 63,411 -2,462,949 -2,399,538

Lateral Bar 4,073,322 -6,520,995 -2,447,673

Slackwater 1,284,016 -4,281,503 -2,997,487

Riffle 841,097 -3,859,136 -3,018,039

Run 95,571 -4,171,501 -4,075,930

Fast Glide 263,713 -5,018,351 -4,754,638

Pool 97,877 -9,768,792 -9,670,915

The fact that some of the MUs occur in regions with high net volumetric changes may be skewed by the large areas that are covered by each MU. For example, the Floodplain MU is represented by a large net fill volume, but also covers a large expanse of valley area. To explore the relative changes that have occurred within each MU, the net volumes were converted into net changes in vertical depth (by dividing volume by area). The net vertical change for all MUs is plotted in Figure 3-18.

Out-of-Channel versus In-Channel Scour and FillWhile the baseflow channel has always shifted its location within the valley (James 2012), the comparative analysis between the 1999 and 2006-2008 topography can quantify the sediment displacement during this natural process. For definition, the term “in-channel” herein describes the region wetted by the 1999 channel, and “out-of-channel” describes the rest of the valley floor. As the flow migrates laterally (or avulsively) through the floodplain sediments, it tends to scour through “out-of-channel” sediments. Those regions outside both the 1999 and 2006-2008 channels are still considered “out-of-channel” and may have a combination of scour and fill due to overbank floods (Figure 3-19).



Figure 3-18. Mean vertical changes (fill, scour, and net) that occurred in the regions that became each MU. The overlain green bars represent the average net change.

Figure 3-19. Example of channel migration between 1999 and 2006-2008. The yellow and green combine to represent the 1999 in-channel region. The blue represents out-of-channel regions that the flow scoured to create new pathways, and the brown represents the remaining out-of-channel regions.



An overlay of the in/out channel regions onto the DoD map reveals the relative volumes of net scour and fill that occurred (Table 3-14). In terms of annual volume, the in-channel regions mostly filled in with sediment (54.7% vs. 45.3%), while the out-of-channel mostly scoured (53.2% vs. 46.8%). This indicates that as the channel migrated to the 2008 location, it tended to fill in its old channel and scour through the floodplains. This result matches up with the previous conclusion that the channel is well connected to the floodplain and that the undersized channel promotes flood-induced scour of the floodplain preferentially compared to the channel.

Table 3-14. Comparison of in-channel and out-of-channel scour/fill rates.In-Channel Out-of-Channel

Annual Volume (ft3/y) Annual Volume (%) Annual Volume (ft3/y) Annual Volume (%)

Scour 2,046,510 45.3 8,281,972 53.2

Fill 2,468,293 54.7 7,272,933 46.8

Net + 421,783 - ̶V 1,009,039 -

Geomorphic Change ProcessesA more in-depth analysis was undertaken to describe and quantify the types of processes that occurred to create the scour/fill patterns noted in the previous sections. The processes were delineated in ArcGIS using a quasi-objective decision tree based on the location of scour and fill with respect to the 1999 and 2006-2008 in/out channel regions. For example, the parts of the scour polygons that intersected with the “inside both 1999 and 2008 channels” polygon would be classified as “downcutting”. While these ‘decisions’ were subjective in nature, once created and decided upon, the delineation and assignment of the polygons becomes objective, based on the decision tree (similar to the baseflow MU delineation methodology). The delineations were created regardless of the MU locations or model hydraulics or magnitudes of the scour and fill, and were based only on the locations of the scour and fill. Regions of “No detectable change” were also delineated as areas in which any topographic variance was too small to be detected within the limits of the DEM differencing method. Scour/fill volumes in these regions are therefore equal to zero. In total, 19 process types (including no change) were identified and delineated, nine each of scour and fill specific processes.

Once the processes were delineated, they could be used as another relevant scale in which to analyze the 7-9 year sediment budget. The DoD raster provides the change in topographic height (scour or fill) for each pixel between 1999 and 2006-2008. Using the Zonal Statistics tool in ArcGIS, the mean topographic height change can be calculated within each process polygon type (i.e., all the scour/fill depths were averaged across all the polygons of one particular process type). However, this had to be done in two steps, because the time epoch for Timbuctoo Bend is different than the rest of the river. To account for this, the mean total depth changes were converted into mean annual volume changes, then summed across the two regions of different time periods, then converted back into total mean annual depth changes. Table 3-15 lists the Yuba Accord M&E Program 33 April 2013Draft Interim Report


processes by type (scour or fill) and gives the relative annual volumetric change for each. At the segment scale, overbank scour and storage processes dominate (~37% for each).

Table 3-15. Relative percent of each scour and fill process. Values represent percent of annual displaced sediment volume from either scour or fill processes.

Scour Process Scour Volume (%) Fill Process Fill Volume (%)

Overbank Scour 37.3 Overbank Storage 37.2

Downcutting 20.1 Vegetated Overbank Storage 32.3

Berm Scour & Mass Failure 16.5 Bar Emergence 13.1

Noncohesive Bank Migration 15.6 In-Channel Fill 5.8

Avulsion 4.1 Island Storage 3.3

Sub-Avulsion 3.1 Vegetated Bar Emergence 3.3

Cohesive Bank Retreat 1.9 Island Emergence 2.0

Island Scour 0.8 Abandoned Channel Infill 1.5

Island Removal 0.6 Vegetated Island Storage 1.5

At the reach scale, the dominant processes vary slightly from the segment scale. Overbank scour and storage processes are still largely ubiquitous, however downcutting is more abundant in the Timbuctoo and Marysville reaches, for example. For fill processes, bar emergence is more dominant in the Dry Creek reach (Table 3-16).

At the MU scale, volumes represent scour/fill processes that had already occurred by the time the MUs were delineated. Table 3-17 lists some major units and their associated abundant processes. For example, of the total volume that had moved in the areas that are now pools, 43% of that was done by downcutting processes. Pools formed purely by downcutting, while riffles formed by channel widening and filling. The results show that riffles and pools are being self-maintained by the river’s hydrologic regime, because pools are scouring down and riffles are remaining higher. This contrasts with other rivers in the Central Valley where scour is always focused on narrow, high riffle crests and pools fill in, yielding long glides with little habitat heterogeneity. The Yuba River experiences a cyclical rejuvenation of its habitat heterogeneity.

Because the channel change processes are not all equal in size, the total volumes of displaced sediments may not accurately represent the relative impact of each process. To wit, the annual volumetric changes were divided by the areas of each process to calculate the average annual rate of vertical change (Figure 3-20). Overbank scour and storage processes displaced the most volume of sediment, but because they cover large areas of the valley, their annual rate of depth change is relatively small compared to other processes (-0.35 and 0.25 ft/yr, respectively). For example, cohesive bank retreat (e.g., cutbanks) exports more than 1.0 ft/yr of sediment, while in-channel fill processes add more than 0.5 ft/yr in deposited sediments.



Table 3-16. Abundant processes at the reach scale. The percentages represent the ratio of sediment volume displaced by the noted process to the total volume of sediment displaced (scour plus fill).

Reach Abundant Scour Processes

(% total volume change)

Abundant Fill Processes

(% total volume change)

Timbuctoo Downcutting(32)

Overbank Storage(4.5)

Parks Bar Overbank Scour(16)

Overbank Storage(19)

Dry Creek Overbank Scour(35)

Bar Emergence(7.4)

DPD Berm Scour(16)


Hallwood Overbank Scour(19)

Veg. Overbank Storage(25)

Marysville Downcutting(23)


Total lower Yuba River

Overbank Scour(19)


Table 3-17. Abundant processes at the MU scale. The percentages represent the ratio of sediment volume displaced by the noted process to the total volume of sediment displaced (scour plus fill).

2009 MU Outcome Abundant Scour Processes(% total volume change)

Abundant Fill Processes(% total volume change)

Pool Downcutting(43)

In-Channel Fill(2.5)

Riffle Non-cohesive Bank Retreat(34)

In-Channel Fill(17)

Slackwater Non-cohesive Bank Retreat(32)

In-Channel Fill(17)

Lateral Bar Overbank Scour(27)

Bar Emergence(23)

Swale Sub-Avulsion(17)

Bar Emergence(15)

Floodplain Overbank Scour(28)


Terrace Overbank Scour(33)


Management OutcomesThe Lower Yuba River has low sinuosity, low entrenchment, and well-connected floodplains. The expected recurrence intervals for bankfull and flood flows are 1.25 and 2.5 years, respectively. These intervals are smaller than for other river systems, but gives further credence to how well-connected the channel is to its floodplains. Other indicators are the fact that the floods fill ~66% of the valley floor, and the presence of swales that inundate at the bankfull flows occur about once every other riffle.

Analyses of the spatial patterns of the morphological units show a deterministic structure. Yuba Accord M&E Program 35 April 2013Draft Interim Report


Because the MU organization is non-random, this indicates that the channel has been self-sustaining for a sufficient duration as to establish an ordered structure. More degraded systems would typically exhibit more homogeneity or randomness.

Figure 3-20. Average annual rates of mean vertical change by process.

The channel exhibits a variety of geomorphology and hydraulics that provide habitat for all lifestages of salmonids. The slackwater and pool MUs represent 16.4% and 15.9% of the total baseflow area, respectively. Additionally, there are multiple side channels and flow bifurcations, as well as backwater areas at higher discharges.

The system is highly dynamic in nature. While the segment exports a small amount of sediment into the Feather River, there are larger scale intra-reach sediment budgets. The Dry Creek reach has experienced the most scour between 1999 and 2008, while the Daguerre Point Dam reach has experienced the most deposition during that same time period. A majority of the 1999 channel experienced fill processes, while more of the 1999 floodplains experienced scour. Overbank scour and storage processes dominate at segment scale. Downcutting dominated in the Timbuctoo reach, while berm scour dominated in the Daguerre Point Dam reach. Pools occur in areas of highest scour volumes (downcutting) of baseflow.



3.2.2 RIPARIAN VEGETATIONBroadly defined, the Valley/Foothill Riparian community is often a transition zone between aquatic and upland terrestrial habitat (The Bay Institute 1998). Due to its location in the transition zone between aquatic and terrestrial ecosystems, the Valley/Foothill Riparian community is characterized by biotic (e.g., species composition) and abiotic (e.g., hydrologic) gradients (Vaghti and Greco 2007 as cited in SAIC 2009). These gradients interact to form highly diverse and complex communities, both structurally and functionally. They also interact strongly with and influence the aquatic, emergent, and upland habitats along their edges.

Riparian habitats support the greatest diversity of wildlife species of any habitat in California, including many species of fish within channel edge habitats (CALFED 2000a). Furthermore, more extensive and continuous riparian forest canopy on the banks of estuaries and rivers can stabilize channels, provide structure for submerged aquatic habitat, contribute shade, overhead canopy, and instream cover for fish, and reduce water temperatures (CALFED 2000a). More extensive and continuous shoreline vegetation associated with instream woody material (IWM) (such as branches and root wads) in shallow aquatic habitats can increase instream productivity and provide for instream structure for juvenile fishes and other aquatic organisms (CALFED 2000a). IWM is of particular importance to riverine ecosystems, and reportedly may be the most important structural component of instream fish habitat (National Research Council 1996).

Although fish species do not directly rely on riparian habitat, they are directly and indirectly supported by the habitat services and food sources provided by the highly productive riparian ecosystem. Riparian communities provide habitat and food for species fundamental to the aquatic and terrestrial food web, from insects to top predators. Riparian vegetation on floodplains can provide additional benefits to fish when the floodplain is inundated, by providing velocity and predator refugia.

In 2012, YCWA conducted a riparian habitat study in the Yuba River from Englebright Dam to the confluence with the Feather River (see Technical Memorandum 6-2 in YCWA 2012). Field efforts included descriptive observations of woody and riparian vegetation, cottonwood inventory and coring, and a large woody material (LWM) survey. The study was performed by establishing eight LWM study sites and seven riparian habitat study sites. One LWM study site was established within each of eight distinct reaches (i.e., Marysville, Hallwood, Daguerre Point Dam, Dry Creek, Parks Bar, Timbuctoo Bend, Narrows, and Englebright Dam). Riparian habitat sites were established in the same locations as the LWM study sites, with the exception of the Marysville study site. Riparian information regarding the Marysville Reach was developed, but no analysis was performed because of backwater effects of the Feather River.



RIPARIAN VEGETATION CHARACTERIZATIONThe RMT contracted Watershed Sciences Inc. to use existing LiDAR to produce a map of riparian vegetation stands by type. The resulting data was subject to a field validation and briefly summarized in WSI (2010) and the data were also utilized in YCWA’s Riparian Study Technical Memorandum 6.2 (YCWA 2012).

Based on field observations, YCWA (2012) reported that all reaches supported woody species in various life stages - mature trees, recruits, and seedlings were observed within all reaches. Where individuals or groups of trees were less vigorous, beaver (Castor canadensis) activity was the main cause, although some trees in the Marysville Reach appeared to be damaged by human camping.

The structure and composition of riparian vegetation was largely associated with four landforms. Cobble-dominated banks primarily supported bands of willow shrubs with scattered hardwood trees. Areas with saturated soils or sands supported the most complex riparian areas and tended to be associated with backwater ponds. Scarps and levees supported lines of mature cottonwood and other hardwood species, typically with a simple understory of Himalayan blackberry or blue elderberry shrubs. Bedrock dominated reaches had limited riparian complexity and supported mostly willow shrubs and cottonwoods.

Based on analysis of mapping data, the majority of the woody species present in the river valley include, in order of most to least number of individuals: various willow species (Salix sp. and Cephalanthus occidentalis); Fremont cottonwood (Populus fremontii) (i.e., cottonwoods); blue elderberry (Sambucus nigra ssp. caerulea); black walnut (Juglans hindsii); Western sycamore (Platanus racemosa); Oregon ash (Fraxinus latifolia); white alder (Alnus rhombifolia); tree of heaven (Ailanthus altissima); and grey pine (Pinus sabiniana). Willow species could not be differentiated by species using remote sensing information. Willow on the lower Yuba River are dominated by dusky sandbar willow (Salix melanopsis) and narrow leaf willow (Salix exigua), and relative dominance of the two species shifts respectively in the downstream direction (WSI 2010). Other species occurring are arundo willow (Salix lasiolepsis), Goodings willow (Salix goodingii) and red willow (Salix laevigata). Goodings and red willow comprise 6.4% of the willow according to a limited field validation survey (WSI 2010).

INVENTORY OF EXISTING COTTONWOOD STANDS Cottonwoods are one of the most abundant woody species in the study area, and the most likely source of locally-derived large instream woody material due to rapid growth rates and size of individual stems commonly exceeding 2 feet in diameter and 50 feet in length. Cottonwoods exist in all life stages including as mature trees, recruits, or saplings, and as seedlings. Cottonwoods are more abundant in downstream areas of the study area relative to upstream. Yuba Accord M&E Program 38 April 2013Draft Interim Report


Cottonwoods are distributed laterally across the valley floor. Of the estimated 18,540 cottonwood individuals/stands, 12 percent are within the bankfull channel (flows of 5,000 cfs or less), and 39 percent are within the floodway inundation zone (flows between 5,000 and 21,100 cfs). However, recruitment patterns of cottonwood have not been analyzed with respect to time or with any more detail regarding channel location.

A total of 97 cottonwood trees were cored to estimate age. Age estimates ranged from 11 to 87 years. The cottonwood tree age analysis resulted in age estimates that place the year of establishment for trees in a range of years from ±7 to 16 years, which is too wide to allow for linking the establishment of trees to any year’s specific conditions.

INSTREAM WOODY MATERIALAbout 8.7 miles of the lower Yuba River downstream of Englebright Dam, distributed among study sites per reach, were surveyed and evaluated for pieces of wood. The number of pieces of wood was relatively similar above and below Daguerre Point Dam (i.e., about 5,100 and 5,750 pieces, respectively). Woody material was generally found in bands of willow (Salix sp.) shrubs near the wetted edge, dispersed across open cobble bars, and stranded above normal high-flow indicators. Most of the woody material was diffuse and located on floodplains and high floodplains, with only about a quarter of the material in heavy concentrations.

Most (77-96%) pieces of wood found in each reach were smaller than 25 ft in length and smaller than 24 inches diameter, which is the definition of large woody material (LWM). These pieces would be typically floated by floodflows and trapped within willows and alders above the 21,100 cfs line, which is defined as the flow delineating the floodway boundary.

Instream woody material was not evenly distributed throughout the reaches. For the smaller size classes (i.e., shorter than 50 ft, less than 24 in diameter), the greatest abundance of pieces was found in the Hallwood or Daguerre Point Dam reaches, with lower abundances above and below these reaches.

The largest size classes of LWM (i.e., longer than 50 ft and greater than 24 inches diameter) were rare or uncommon (i.e., fewer than 20 pieces total) with no discernible distribution. Pieces of this larger size class were counted as “key pieces”, as were any pieces exceeding 25 inches in diameter and 25 feet in length and showing any morphological influence (e.g., trapping sediment or altering flow patterns). A total of 15 key pieces of LWM were found in all study sites, including six in the Marysville study site. Few of the key pieces were found in the active channel or exhibiting channel forming processes.

3.2.3 FLOWSStreamflow quantity and timing are critical components of water supply, water quality, and the ecological integrity of river systems (Poff et al. 1997). Streamflow, which is strongly correlated with many critical physicochemical characteristics of rivers, can be considered a master variable Yuba Accord M&E Program 39 April 2013Draft Interim Report


that limits the distribution and abundance of riverine species (Power et al. 1995 and Resh et al. 1988 in Poff et al. 1997) and regulates the ecological integrity of flowing water systems.

COMPARISON OF PRE-ACCORD AND ACCORD FLOWSPre-Accord flows (i.e., 1999 through 2005) were predominantly governed by RD-1644 flow requirements, while current flows (i.e., 2006 through 2012) in the lower Yuba River are regulated by the Yuba Accord. One important caveat to comparison of flows in the lower Yuba River is the difference in hydrologic and climatologic conditions between periods used to represent pre-Accord and Accord flows. Hydrologic and climatologic conditions differed considerably during the 1999–2005 and 2006–2012 periods, not only in total annual precipitation and runoff, but also with regard to the timing and magnitude of runoff and inflow to New Bullards Bar and Englebright reservoirs. As a result, these comparisons are illustrative but do not represent the range of conditions and associated flows in the lower Yuba River under Yuba Accord operations, relative to pre-Accord conditions. It is anticipated that the operations model currently being developed for the YRDP relicensing process could provide a more representative comparison of pre-Accord and Accord flow regimes in the lower Yuba River.

Flow monitoring results for the lower Yuba River are displayed in the following figures. Time series of mean daily flows at the Smartsville and Marysville gages from January 1999 through November 2012 are displayed in Figures 3-21 and 3-22, respectively. Figure 3-23 and Figure 3-24 display monthly flow exceedance probability distributions for pre-Accord years (1999-2005) and for Accord years (2006-2012) at the Smartsville Gage, and Figure 3-25 and Figure 3-26 display monthly flow exceedance probability distributions for pre-Accord years and for Accord years at the Marysville Gage.

3.2.4 WATER TEMPERATURES Water temperature is one of the most important environmental parameters affecting the distribution, growth, and survival of fish populations. Lethal water temperatures affect fish populations by directly reducing population size, while sub-lethal water temperatures affect fish populations via indirect physiologic influences. Elevated water temperatures can generally affect individuals by increasing respiration and metabolism, increasing growth rates, reducing resistance to diseases, decreasing reproductive fitness and success, reducing resistance to predation, and increasing mortality rates.

Water temperatures may particularly regulate fish populations that are near their latitudinal distributional extremes, because environmental conditions (e.g., water temperature) at distributional extremes also may be near the boundaries of conditions that allow the populations to persist. For example, California’s Central Valley is at the southern limit of Chinook salmon distribution, and studies have demonstrated that direct effects of high water temperatures are an important source of juvenile Chinook salmon mortality in the Central Valley (Baker et al. 1995).Maintenance of stream temperatures is important not only for individual species, but also because temperature drives primary production rates and can influence mobilization rates of Yuba Accord M&E Program 40 April 2013Draft Interim Report


toxics and nutrients (e.g., development of toxic algal blooms from cyanobacteria) (Swanson 2008 as cited in CDFG 2008a).

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Figure 3-21. Mean daily flow at the Smartsville Gage during January 1999 through November 2012.

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Figure 3-22. Mean daily flow at the Marysville Gage during January 1999 through November 2012.

Figure 3-23. Pre-Accord and Accord mean daily flow exceedance probability distributions at the Smartsville Gage during January through June.


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Figure 3-24. Pre-Accord and Accord mean daily flow exceedance probabilities at the Smartsville Gage during July through December.


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Figure 3-25. Pre-Accord and Accord mean daily flow exceedance probability distributions at the Marysville Gage during January through June.


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Figure 3-26. Pre-Accord and Accord mean daily flow exceedance probability distributions at the Marysville Gage during July through December.

Water temperature regimes occurring in regulated rivers are controlled by climatologic and Yuba Accord M&E Program 45 April 2013Draft Interim Report


meteorologic conditions, the physical characteristics of the regulating dams and reservoirs, the volume, timing, and temperature of inflows to the reservoirs, and the release schedules associated with dam and reservoir operations. Water temperatures in the lower Yuba River downstream of Englebright Dam are influenced by the magnitude and temperature of the water released from New Bullards Bar Reservoir to Englebright Reservoir, the magnitude and temperature of inflow to Englebright Reservoir from the South and Middle Yuba rivers, releases from the Narrows I and II powerhouses and bypasses below Englebright Dam (and spills over Englebright dam) to the lower Yuba River, operations under the Yuba Accord Fisheries Agreement (magnitude, frequency, and duration of water releases), and natural mechanisms of heat transfer associated with characteristics of the physical environment (e.g., river geometry) and climate (e.g., ambient air temperatures, cloud cover, etc.).

Operational releases at Englebright Dam (~RM 24) provide the base flow and water temperature boundary conditions in the upper reaches of the lower Yuba River. Further downstream (RM 22.7 and below), lower Yuba River flows and water temperatures during certain periods of the year are affected by inflows from Deer Creek (RM 22.7) and Dry Creek (RM 13.6), and by irrigation diversions at Daguerre Point Dam (DPD) (RM 11.6). Additionally, substantial heat transfer into the lower Yuba River occurs as a result of surface water-air interaction and solar radiant heating. The river channel is generally wide and flat (except in the Narrows Reach) which promotes significant heat transfer at the water-air interface (YCWA et al. 2007). These high surface width-to-flow ratios also facilitate solar radiant heating.

Water temperature modeling conducted as part of the Yuba Accord EIR/EIS (YCWA et al. 2007) indicated that temperatures in the lower Yuba River during summer and fall months would generally be colder by 1°F to 5°F (depending on hydrologic conditions and release schedule) under Yuba Accord operations compared to historical conditions. The suitability of water temperatures for fish species of focused evaluation in the lower Yuba River are provided and discussed in Chapter 5 of this report. Monitored water temperatures during pre-Accord years (i.e., 1999 through 2005) and during Accord years (i.e., 2006 through 2012) are compared below.

COMPARISON OF PRE-ACCORD AND ACCORD WATER TEMPERATURES

Water temperature monitoring results for the lower Yuba River are displayed in the following figures. Time series of mean daily water temperatures at the Smartsville Gage (during October 2002 through October 2012) and at the Marysville Gage (from January 1999 through October 2012) are displayed in Figure 3-27 and Figure 3-28, respectively. Figure 3-29 and Figure 3-30 display water temperature exceedance probability distributions for pre-Accord years (1999-2005) and for Accord years (2006-2012) at the Marysville Gage. Water temperature exceedance probability distributions are not displayed and compared during pre-Accord and Accord years at the Smartsville Gage because water temperature data are only available for approximately 3 years prior to implementation of the Yuba Accord.

As previously stated for the pre-Accord and Accord flow comparisons, an important caveat to Yuba Accord M&E Program 46 April 2013Draft Interim Report


comparison of water temperatures is the difference in hydrologic and climatologic conditions between the periods used to represent pre-Accord and Accord water temperatures. These differences include total annual precipitation and runoff, as well as the timing and magnitude of runoff and inflow to New Bullards Bar and Englebright reservoirs. As a result, these comparisons of water temperature are illustrative but do not represent the range of conditions and associated water temperatures in the lower Yuba River under Yuba Accord operations, relative to pre-Accord conditions. It is anticipated that the operations and water temperature models currently being developed in the YRDP relicensing process will provide a more representative comparison of pre-Accord and Accord water temperature regimes in the lower Yuba River.

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Figure 3-27. Mean daily water temperatures at the Smartsville Gage during October 2002 through October 2012.

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Figure 3-28. Mean daily water temperature time series at the Marysville Gage during January 1999 through October 2012.


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Figure 3-29. Pre-Accord and Accord mean daily water temperature exceedance probability distributions at the Marysville Gage during January through June.


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Figure 3-30. Pre- Accord and Accord mean daily water temperature exceedance probability distributions at the Marysville Gage during July through December.



Figures 3-29 and 3-30 (above) indicate that monitored water temperatures in the lower Yuba River at the Marysville Gage (during calendar years 1999-2012) are generally lower during the warmest months of the year (i.e., April through September) of the Accord years (2006-2012), relative to the pre-Accord years (1999-2005). During December, February, and March, water temperatures are higher during the Accord years more often, but are lower over the warmest portions of the distributions. Water temperatures during October are generally similar during the pre-Accord and Accord years. During January and November, water temperatures are higher over the entire distributions during the Accord years, but water temperatures are always below about 51°F and 59°F, respectively. Detailed month-by-month comparisons of water temperature exceedance probabilities during Accord years, relative to pre-Accord years at the Marysville Gage are provided below, with an emphasis on the warmest portions of the distributions.

During January, water temperatures are higher during the Accord years over the entire distribution, but water temperatures are always below about 51°F.

Water temperatures during February are higher during the Accord years over about 80% of the distribution, but are lower during the warmest 20% of the distribution, and are always below about 52°F.

March water temperatures are both higher and lower over about 50% of the distribution, but are lower during the warmest 50% of the distribution by approximately 1.5°F.

April water temperatures are lower during the warmest 70% of the distribution by about 1 to 2°F.

Water temperatures during May are lower during the warmest 60% of the distribution, and are lower by about 3 to 4 °F during the warmest 20% of the distribution.

Water temperatures during June are lower over the entire distribution, and are lower by about 2 to 4°F during the warmest 15% of the distribution.

July water temperatures are similar over about 60% of the distribution, are lower over about 40% of the distribution, and are lower by about 2 to 4°F during the warmest 15% of the distribution.

August water temperatures are higher by about 1°F during 30% of the distribution, but are lower during the warmest 50% of the distribution by about 2 to 3°F.

September water temperatures are lower over about 70% of the distribution, and are lower by about 1 to 2°F during the warmest 20% of the distribution.

Water temperatures during October are generally similar over most of the distribution.

November water temperatures are higher over the entire distribution by about 1 to 2°F, but are below 58 °F about 95% of the time.

December water temperatures are higher during about 55% of the distribution by about 2°F (when water temperatures are always below 50°F), and are lower during the warmest 25% of the distribution by about 1°F.


me report/m and e interim chapt… · web viewthe blue represents out-of-channel regions that the...

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