draft technical memorandum5counties.org/docs/projects/sgfs1_geomoprh_tm.pdf · sidney gulch and its...

TECHNICAL MEMORANDUM

Date: December 31, 2014

To: Sandra Perez, Five Counties Salmonid Conservation Program

From: Rachel Shea, P.E., Engineering Geomorphologist, Michael Love & Associates, Inc.

Michael Love, P.E., Principal Engineer, Michael Love & Associates, Inc.

Subject: Preliminary Channel Design Recommendations for the Sidney Gulch Channel Restoration at the USFS Compound in Weaverville, CA

MEMORANDUM PURPOSE

This technical memorandum (TM) provides a brief discussion of the existing condition channel morphology of Sidney Gulch, which flows through Weaverville, California. The TM also presents channel design recommendations for a planned restoration of the existing concrete channel reach of Sidney Gulch and its tributaries, Ash Hollow and Garden Gulch, within the U.S. Forest Service (USFS) compound (project area), which is located between Highway 299 and Forest Avenue. The findings and recommendations presented in this TM are intended to guide project design development.

INTRODUCTION

Background Sidney Gulch is a perennial stream with its headwaters originating in the Shasta-Trinity National Forest. The steep upstream reaches of Sidney Gulch have been logged in the past, and have experienced severe wildfires in recent years. Like many of the streams in the area, the streambed and banks along Sidney Gulch were highly disturbed from historical hydraulic mining. The geology of the region, the ground disturbances from past land use activities, and recent wildfires result in a substantial amount of sediment being delivered to Sidney Gulch.

The lower reaches of Sidney Gulch flows through the town of Weaverville, where much of the stream and its tributaries have been straightened, are highly confined, and are moderately entrenched. One section of the stream has been placed in a concrete lined channel while other sections have riprap or retaining wall lined banks.

The stream restoration project area is located within the USFS compound between Highway 299 and Forest Avenue, and contains the mainstem channel of Sidney Gulch and the tributary channels of Ash Hollow and Garden Gulch. All three consist of concrete trapezoidal channels. Beyond the project area these streams return to natural-bed channels, with the exception of road-stream crossings.

Preliminary Channel Design Recommendations for the Sidney Gulch Channel Restoration

Michael Love & Associates, Inc.

Project Goals and Objectives The goals for this project are to restore the existing concrete channel reaches of Sidney Gulch and the Ash Hollow and Garden Gulch tributaries between Highway 299 and Forest Avenue with geomorphically functioning natural channels that improve aquatic habitat and fish passage, and reduce flooding of adjacent properties. Specific objective include:

• Replacing the existing concrete channel with a self-sustaining natural stream channel,

• Improving fish passage and creating spawning and rearing habitat within the project reach,

• Reducing the magnitude and frequency of out-of-bank flooding,

• Conveying the sediment load delivered from upstream, and

• Minimizing removal of, and disturbance to, large native trees.

This TM focuses specially on the preliminarily geomorphic design of the Sidney Gulch stream channel and its tributaries within the project reach, including channel hydraulic geometry and sediment transport competence. Further analysis will be necessary to evaluate the flooding reduction that can be expected with the project.

Previous Work in the Project Area Topographic Survey In 2013 and 2014, the Five Counties Salmonid Conservation Program (5C) conducted a topographic survey of the USFS Compound, and also conducted a thalweg survey and cross sections along of Sidney Gulch extending from upstream of the Weaver Bally Loop to Bremer Street. The survey was based on an assumed datum and included numerous stream crossings. Michael Love & Associates, Inc. (MLA) has since performed addition survey with 5C to supplement this survey and create a topographic basemap tied to the California State Plane Zone 1 (NAD83) horizontal datum and NAVD88 vertical datum. The project basemap is provided in Attachment 1.

An additional 1,700 feet of topographic survey was performed downstream of Bremer Street by Graham Matthews & Associates (GMA) as part of a separate 5C project to restore Sidney Gulch in Lee Fong Park. This survey data was used to extend the downstream channel thalweg profile.

HEC-RAS Hydraulic Analyses 5C prepared a HEC-RAS model that extended from Bremer Street to upstream of the Weaver Bally Loop culvert crossing and included 7 stream crossings (5C, 2013 and 2014). The model was prepared in an assumed datum and was used to evaluate 2-year through 100-year flow events. Peak flows were estimated using regional regression equations by Waananen and Crippen (1977).

Sidney Gulch and the Garden Gulch and Ash Hollow tributaries downstream of Highway 299 are located within a FEMA-mapped flood zone (Zones AE and AO) on FEMA FIS Map Number 06105C1027E (FEMA, 2010). Zones AE and AO denote inundation areas determined using detailed hydraulic analysis, and include Base Flood elevations. FEMA defines the Base Flood as the 100-year flow (1 percent annual exceedance probability). Base Flood flows and water surface elevations for Sidney Gulch are presented in ACOE (1989).



Because the model was prepared using an assumed datum, use of the FEMA-derived Base-Flood WSE was not possible. However, the 5C HEC-RAS model was useful in evaluating the existing-condition hydraulic capacity of the stream crossings and concrete channel within the model domain.

Geotechnical Assessment A geotechnical investigation of the project reach was conducted by CGI Technical Services, Inc. (CGI Technical Services, Inc., 2014). The investigation included excavation of 10 test pits, each about 6.5 feet deep. The underlying materials consist of dense sandy gravels, and in some locations, cobbles up to 6-inches in diameter at about 5-foot depths. Recommended maximum side-slope for finished slopes is 2H:1V. Materials on site are suitable for engineering fill, with the exception of the clays observed in some of the test pits.

Project Approach Preliminary design development for the Sidney Gulch channel restoration was based on natural channel design methodologies (USFS, 2008, NRCS, 2007). The natural channel design methodology results in the design channel having similar geomorphic form and function as a reference reach located in a nearby stable channel reach. Reference reach-based channel design is conducted using a combination of hydrologic, geomorphic and hydraulic analyses of adjacent stable channel reaches.

Because Sidney Gulch has been highly disturbed, identification of a suitable reference reach in Sidney Gulch was difficult. However, preliminary field observations of the stream channel upstream and downstream of the project area resulted in the identification of localized reaches of channel that appeared to be moderately stable, transporting the delivered sediment load, and exhibited, though weakly, desirable pool habitat or localized depositional features such as point bars or inset floodplains. Though not an optimal stable natural channel, these reaches reflect stable hydraulic geometry, sediment transport, and in-stream habitat characteristics used as baseline values for developing an appropriate channel design in the project reach.

Peak Flow Hydrology Peak flows with return periods ranging from the 1.1- to 100-year return periods were computed for various locations along Sidney Gulch and the tributaries within the project reach using the North Coast Regional Regression Equations developed by the USGS (Gotvald et al., 2012). Flows were computed using basinwide mean annual precipitation depths (PRISM, 2000) as shown in Table 1 and Attachment 2. Flows with less than a 2-year return period were logarithmically extrapolated from the computed values.

Flows in Sidney Gulch downstream of the Garden Gulch and Ash Hollow tributary confluence were added to flows in Sidney Gulch. Because of only a slight difference in watershed size, flows in Sidney Gulch at Oregon Street were assumed to be similar to flow at Forest Avenue.

Flows predicted using Gotvald, et al., (2012) are higher than flows previously computed by 5C using Waananen and Crippen (1977), as presented in 5C (2013, 2014).



Table 1: Return period flows computed using the North Coast Regional Regression Equations (USGS, 2012).

Location Drainage Area Return Period of Peak Flow

1.1-Year1 1.5-Year1 2-Year 5-Year 10-Year 25-Year 50-Year 100-Year3

Sidney Gulch at Reference

Reach 1.58 mi2 40 cfs 78 cfs 113 cfs 225 cfs 308 cfs 417 cfs 501 cfs 590 cfs

Sidney Gulch at 299 2.56 mi

2 60 cfs 117 cfs 170 cfs 338 cfs 460 cfs 623 cfs 749 cfs 881 cfs

Garden Gulch at 299 2.49 mi


Ash Hollow at 299 0.27 mi


Sidney Gulch at Oregon St.2 5.22 mi

2 12 cfs 243 cfs 354 cfs 707 cfs 966 cfs 1,310 cfs 1,576 cfs 1,855 cfs 1 Extrapolated 2 Sum of flows from Sidney Gulch at 299, Garden Gulch and Ash Hollow 3 FEMA 100-Year flow in Sidney Gulch upstream of Garden Gulch confluence = 1,005 cfs (2.71 mi2) (ACOE, 1989)

GEOMORPHIC EVALUATION

Overview The concrete channel of Sidney Gulch within the project area is trapezoidal with an approximately 14-foot wide bottom and 4-foot high concrete banks, as shown in Figure 1. The channel overbanks are relatively steep. Upstream and downstream of the project area, the stream channel has a natural channel bottom, is relatively straight, moderately entrenched and has a mix of natural banks, riprap, and various types of retaining walls. Where unarmored channel banks are present, they appear to be relatively stable. The streambed within the more natural, less armored, reaches is typically featureless and formed of gravels, cobbles and occasional small boulders. Riparian areas are relatively narrow and sparse, with English ivy the primary understory plant in many locations.

A thalweg profile extending from the Weaver Bally Loop through Bremer Street is presented in Figure 2. Sidney Gulch exhibits variable channel slopes ranging from 1.20% to 2.86%. The concrete channel slope within the project area is nearly 2%. There is nearly a 6-foot drop in the channel thalweg over a short distance through the Forest Avenue stream crossing. The drop is a combination of the steeply sloped concrete apron extending through the bridge crossing and a long scour pool downstream of the concrete apron. The drop at the Forest Avenue crossing creates a discontinuity in the channel profile, suggesting that the channel downstream of Forest Avenue has historically incised while the concrete has prevented upstream incision.

The natural-bed channel reaches of Sidney Gulch between the Weaver Bally Loop and Bremer Street can be classified as a plane-bed channel (Montgomery and Buffington, 1997). Plane-bed channels are relatively straight, low width to depth ratio, moderately entrenched channels. Generally, plane-bed channels lack pools or depositional features, except where flow obstructions such as boulders, log jams or planimetric features force the development of these features. Forcing features are uncommon within Sidney Gulch, primarily due to channel straightness and the lack of large wood or boulders within the channel. Where forcing features are present in the channel, pools and minor depositional features were observed.



Figure 1. Concrete channel within the Sidney Gulch project reach.

To evaluate the existing channel capacity within the project reach and to understand the potential effects of stream crossings along Sidney Gulch on channel geomorphology, MLA updated the preliminary HEC-RAS analyses prepared by 5C with peak flows computed using Gotvald et al., (2012) and presented in Table 1. Model-predicted water surface profiles for the 1.1-, 5- and 50-year flows are presented in Figure 3.

The preliminary HEC-RAS modeling indicated that the concrete channel within the project area conveys approximately the 10-year flow before out-of-bank flooding occurs. The modeling also showed that several of the stream crossings through Weaverville are substantially undersized. Undersized crossing can cause backwatering and sediment aggradation upstream of crossings, debris plugging, and sediment deficits downstream of the crossings, resulting in channel downcutting and entrenchment. At the Weaver Bally Loop and Memorial Drive crossings, flows can be expected to overtop the roadways during an approximately 5-year flow event, at Highway 299 during a 5- to 10-year flow event, and at Forest Avenue between a 10- and 15-year flow event. The sediment aggradation upstream of the Weaver Bally Loop crossing, and channel incision downstream of the crossing is evident in Figure 3. Given the backwatering that occurs during fairly frequent flow events, similar aggradation may be occurring, or could occur in the future, upstream of Memorial Drive and Highway 299 following future replacement of the Weaver Bally Loop crossing. Replacement of the Weaver-Bally Loop crossing is planned by 5C in the near future.



Figure 2. Longitudinal thalweg profile of Sidney Gulch. Dashed lines represent overall slope of an individual channel reach. Stream crossings are shown as triangles and cross section locations in baseline reaches are shown as circles. The gap in data between Highway 299 and the Weaver Bally Loop is where a continuous thalweg survey was not performed.

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Figure 3. Preliminary HEC-RAS predicted 1.1-, 5- and 50-water surface profiles in Sidney Gulch between the Weaver Bally Loop and Bremer Street. Grey ground points indicate cross sections interpolated from adjacent surveyed cross sections. Note that stationing and elevations are assumed and do not correspond to Figure 1.

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Geomorphology of Baseline Reaches Three channel reaches were selected for geomorphic evaluations that represent baseline condition in moderately stable natural-bed channel reaches of Sidney Gulch, as presented in Figure 4. These included a channel reach surveyed by MLA approximately 4,000 feet upstream of Memorial Drive (Upstream Reach), a channel reach downstream of the Weaver Bally Loop crossing (Weaver Bally Reach), and a reach downstream of Oregon Street (Oregon Street Reach).

A summary of the measurements and computations performed for the baseline reaches are presented in Attachment 3.

Figure 4. Locations of baseline reaches surveyed in Sidney Gulch.



Upstream Reach

The Upstream Reach (Figure 4) consisted of an approximately 300-foot long plane-bed forested channel reach located upstream of a recently burned area. Underbrush in the forest was sparse and the area has been burned in the recent past. This channel reach was selected for analysis because it appeared to have a similar slope, channel entrenchment, and valley width as the project reach. Though the Upstream Reach has been subject to substantial sediment deposition in the past, the channel has since cut down through the deposition and began to develop riffles, pools, and some depositional features. Bedrock and decomposing bedrock was evident in some of the pools. Weak bankfull indicators consisting of slope breaks along the banks and minor deposition were present in this reach.

MLA performed a survey of the channel thalweg profile and two cross sections, measured active channel, bankfull and valley widths, conducted one pebble count. MLA also measured individual large cobles and boulders not captured in the pebble count but had been mobilized by the channel to form small step features within riffles. 5C also performed a pebble count in this area.

The overall slope of the Upstream Reach is about 2.2%. Active channel widths (channel bottom width) ranged from 6 to 7.5 feet, with an average of 7.1 feet. Bankfull widths ranged from 10 to 12.6 feet, with an average of 11.3 feet. The channel depth at bankfull indicators ranged from 1.1 to 2.4 feet, with an average of 1.5 feet. Valley widths ranged from 60 to 107 feet. This reach of channel exhibited relatively low sinuosity, but did have several meander bends. Pools were limited to the downstream end of riffles and on meander bends. Measured pool depths were less than 1.0 feet deep.

The pebble counts conducted by 5C and MLA yielded similar results (Figure 5), with 50% of the particles (D50) between 35 and 50 mm, and 84% of the particles (D84) smaller than 90 to 110 mm. The large particles forming steps within the riffles range from 80 to 280 mm, and fall within the D90 to D100 of the two pebble counts.

Weaver Bally Reach The selected channel reach between the Weaver Bally Loop and Memorial Drive (Figure 4) is a relatively straight plane-bed channel that contains a discontinuous earthen berm along one side. The berm supports trees of about 1-foot in diameter. This reach of channel likely receives only limited sediment supply from upstream due to sediment storage upstream of the undersized crossing at Weaver Bally Loop. Therefore, the upstream reaches of this channel near the Weaver Bally Loop culvert outfall have downcut, exposed decomposing bedrock, and exhibit poor riffle development due to lack of sediment. However, riffle and pool formation, as well as weak point bar and inset floodplains development become evident further downstream. Weak bankfull indicators including point bars and inset floodplains were present in this reach. This reach was selected for evaluation in part because it represents the sediment supply reach for the project area.

Two cross sections surveyed by 5C were evaluated within this reach at the locations shown in Figure 2. Near the vicinity of the cross sections, MLA measured active channel and bankfull widths, conduced a pebble count, and measured individual large cobles and boulders, not included in the pebble count, that had been mobilized by the channel to form small step features within riffles.

The overall slope of the reach is 1.65%. Measured active channel widths ranged from 6 to 9 feet, averaging 7.6 feet, and bankfull width ranged from 9 to 16 feet, with an average of 12.8. Bankfull depth measured at one of the sections was 1.8 feet deep. The other section did not have a clear bankfull indicator.



The bed material gradation in this reach estimated using a pebble count was similar to the gradation in the Upstream Reach (Figure 5), with 50% of the particles (D50) smaller than about 30 mm, and 84% of the particles (D84) smaller than 65 mm. The large particles forming steps within the riffles range from 90 to 200 mm, and fell within the D95 to larger than the D100 of the pebble count.

Oregon Street Reach The channel reach between Oregon Street and Lorenz Road (Figure 4), and within the Joss House State Park, is a relatively straight plane-bed channel. The south channel bank is stable and gently sloping, and exhibits a small inset floodplain. The north bank is steep and confined by a gabion retaining wall. Since the installation of the wall, a bankfull bench and a young riparian forest have developed adjacent the gabion wall. In addition to showing some desirable geomorphic feature development, this reach was selected for evaluation because of it represents the channel reach that will receive sediment delivered from the project reach. Weak bankfull indicators including a small inset floodplain and breaks in slope were present in this reach.

Two cross sections surveyed by 5C were evaluated within this reach, as shown in Figure 2. Near the vicinity of the cross sections, MLA measured active channel and bankfull widths. Measured active channel widths ranged from 9.5 to 12 feet, and bankfull width ranged from 12.5 to 15.7 feet Bankfull depth ranged from 1.6 to 2 feet. The overall slope of the reach is 1.7%.

Figure 5. Pebble Count results from the Upstream and Weaver Bally Reaches. Individual markers represent the largest mobile grain sizes measured in each reach.

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Largest size moved, UpstreamReachWeaver Bally Reach

Largest Size Moved WeaverBally



Hydraulic Geometry Analysis of Baseline Reaches Normal-depth hydraulic computations at two cross sections in each reach were performed using the WinXSPro (USFS, 2005) software. The results of the computations were used to evaluate flood frequency associated with the bankfull features observed in the field, and to compute hydraulic geometry and sediment transport competence of each reach. For the analysis, slope was based on the overall slope of the reach. Depth-dependent channel roughness was estimated using Limerinos (1970). The D84 of pebble count data in the Upper and Weaver Bally reaches were used for the analysis, and was also assumed to be suitable for a preliminary analysis of the baseline reach downstream of Oregon Street.

The hydraulic analysis indicted the observed bankfull indicators coincide with the 1.1- to 1.8-year return period flow, with an average return period of 1.4 years. Bankfull flows have been found to commonly have a return period between 1.2- and 1.5-years and serve as the dominant “channel forming” flow, which shapes the active channel of a stream (Wolman et al., 1960).

Hydraulic geometry of the baseline channel sections were based on field bankfull indicators. At this flow the max water depth (measured from the thalweg) and the width/depth ratio (W/d, calculated using hydraulic depth) were calculated. Also evaluated were the entrenchment ratios (flow width/bankfull width) associated with 2-year and 5-year return period flows. The results of the hydraulic computations are summarized in Table 2 and presented in Attachment 3.

Table 2. Summary of channel hydraulic geometry in the three baseline reaches of Sidney Gulch.

Location Slope Bankfull (Field Indicators) 2-Year

Entrenchment Ratio

5-Year Entrenchment

Ratio Width/depth

Ratio Return Period

(years) Upstream Reach - Section 1 2.10% 14.5 1.1 1.5 1.8 Upstream Reach - Section 2 2.10% 11.5 1.4 1.4 3.6 Weaver Bally Station 65+96 1.65% - - - - Weaver Bally Station 63+88 1.65% 10.7 1.8 0.8 1.0

Oregon Station 26+12 1.67% 9.4 1.5 1.2 1.5

Oregon Station 25+72 1.67% 11.1 1.1 1.6 2.0

Minimum 1.65% 9.4 1.1 0.8 1.0 Maximum 2.10% 14.5 1.8 1.6 3.6 Average 1.81% 11.4 1.4 1.3 2.0

Sediment Transport Analysis of Baseline Reaches A competence-based sediment transport analysis of the baseline channel reaches was conducted to evaluate sediment delivery to and from the project reach. Sediment transport competence is a measurement of a flow’s ability to mobilize or entrain a given size sediment particle and is typically evaluated using channel shear stress. If the shear stress is greater than the entrainment shear stress of the particle, it will be mobilized. The sediment transport analysis was conducted assuming the “Equal Mobility Theory,” which postulates that once the median diameter (D50) grain size is moved in a stream channel, the entire bed has mobilized, including the larger particles (Parker et al., 1982).



The entrainment shear stress for a given particle can be estimated using the Shields Equation and an estimate of critical dimensionless shear stress. Channel shear stress was obtained from the WinXSPro results for a range of flows at each baseline cross section. A critical dimensionless shear stress value of 0.04 was used, which reflects typical gravel bed conditions with a small amount of sand (Wilcock, et al., 2009).

The results of the sediment transport analysis are presented in Figure 6. The Upstream Reach and Weaver Bally Reach reflect the sediment source reaches, because they transport sediment to the project reach. The Oregon Street Reach reflects the receiving reach because it will receive sediment delivered from the project reach. Though a lower slope, the receiving reach has a higher transport competence because of inflows from the Ash Hollow and Garden Gulch tributaries.

The sediment transport analysis indicates that flows as low as the 1.1-year return period have the competency to mobile an 80 mm particle, which is substantially larger than the D50 grain size in the pebble counts. This indicates that the channel bed within the baseline reaches is fully mobile during a 1.1-year flow event, including the largest particles that were observed forming structural features within riffles.

Detailed results of the sediment transport analysis are presented in Attachment 3.

Figure 6. Competency-based sediment transport analysis for selected baseline channel sections in Sidney Gulch. The colored symbols represent the sediment competence of the baseline reaches and the black squares represent the sediment competence of the typical design cross section.

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Upstream Reach - Section 1 Upstream Reach - Section 2Weaver Bally Sta. 65+96 Weaver Bally Sta. 63+88Oregon Sta. 26+12 Oregon Sta. 25+72Design Cross Section Log. (Upstream Reach)Log. (Weaver-Bally) Log. (Oregon)



PRELIMINARY DESIGN

Preliminary design plans for the project are shown in Attachment 5.

Constraints There are several land-use constraints that define the available corridor width for restoration of Sidney Gulch and its tributaries within the USFS Compound. There are several buildings, a road, and parking areas south of the channel within the compound. Assuming parking spaces adjacent to the south bank of Sidney Gulch can be relocated, as previously discussed by the project stakeholders, the stream corridor could be widened on the south side of the channel while maintaining the existing road and buildings.

Along the north side of the Sidney Gulch channel and adjacent to the tributaries, the project area contains buildings, parking areas, and lawns that are lightly forested with both native and non-native trees and occasional shrubs. USFS has indicated that, to preserve the historical appearance of the area, it is desirable to retain large native trees, specifically oaks and sycamores, and also other large native trees such as cottonwood and maple trees. This constrains the available width along Sidney Gulch and its tributaries for use in restoration.

Sidney Gulch Design Objectives A moderately entrenched plane-bed channel was selected as the target channel type for Sidney Gulch. A plane-bed channel will function similarly to the channel reaches upstream and downstream of the project area, maintaining sediment transport continuity through the project reach while providing opportunities to improve fish passage and aquatic habitat.

The width of the available stream corridor allows some space for limited channel sinuosity appropriate for this type of channel. The corridor width also allows for small sloping floodplains on one or both sides of the stream channel. The combination of the floodplains and channel planform, with selective placement of forcing features such as boulders or large wood, can be used to create a diversity of flow conditions and to force scour pools that can be used by fish for cover and rearing habitat. The forcing features will also create localized areas of sediment aggradation that can augment channel complexity and provide spawning areas. The floodplain will increase flood conveyance and reduce shear stresses within the channel. The reduction of shear stress will lower the potential of redd scour and create areas where natural gravel recruitment can occur.

Planform The width of the available corridor allows construction of a stream channel with limited sinuosity. For preliminary design, a sinuosity of 1.025 was assumed. The sinuosity allows for the presence of alternating floodplains along the channel and large wood-forced scour pools on the outside of the meander bends. The available channel corridor is wider near the Highway 299 crossing and downstream of the Ash Hollow Tributary confluence, allowing for a broader channel planform and wider floodplains.

Profile There is nearly a 6-foot drop in the channel thalweg through Forest Avenue stream crossing, as evident in Figure 2. It is recommended that the design profile for the project reach meet the existing channel grade downstream of this drop, as shown in Figure 7. This will eliminate a short reach of steep channel



slope that likely is a partial fish passage barrier and will create a stable channel profile. To achieve the design profile, the crossing at Forest Avenue will require modification to lower the channel bottom. Review of the as-built plans or structural inspection is recommended to identify feasible modification options or if a full replacement may be necessary. Lowering the channel bottom through the crossing would also improve flood conveyance through the crossing and increase overall hydraulic capacity of the restored channel corridor.

The stream crossing at Highway 299 is substantially undersized, predicted to overtop during a 5- to 10-year flow event. It is also a partial fish passage barrier. At some point in the future, this crossing will be likely be replaced with a full spanning crossing with a natural channel bottom. Therefore, the design profile through the project reach was developed to accommodate a future crossing replacement, meeting the existing channel grade at the existing upstream invert elevation of the Highway 299 crossing, as shown in Figure 7. Between the time that the channel is restored within the USFS Compound and the Highway 299 crossing is replaced, an interim channel consisting of step pools or weirs passable for fish can be constructed to transition the channel profile to the Highway 299 culvert invert. A 4% interim transition profile for the channel is shown in Figure 7.

The channel restoration reach will extend approximately 1,200 feet. With a sinuosity of 1.025, the overall design channel profile will have a slope of 2.11%, which accounts for the increased sinuosity. The profile will include plane-bed reaches and pools associated with the channel planform and forcing features.

Cross Section A cross section shape was developed for the channel that represents a typical cross section within the narrowest part of the channel corridor upstream of the Ash Hollow tributary (Figure 8). The hydraulic geometry of the cross section was based on the baseline channel hydraulic geometry and a sediment competency analysis that indicates the design channel will support sediment transport continuity from upstream during larger flow events.

The channel was designed to have a bankfull W/d ratio of 13.2, which is slightly larger than the average w/d ratio of 11.4 observed in the baseline reaches. The larger W/d ratio was selected to reduce channel velocities and shear stresses that will facilitate bank stability and fish passage, and will promote gravel recruitment during more frequent flow events. A 2-year entrenchment value of 1.3 was selected, which is close to the average value observed in the baseline reaches.

The typical cross section consists of a 10-foot wide active channel width with banks having 2H:1V side slopes (Figure 8). At a depth of 1.5 feet, the channel width would be 15.6 feet wide. At this depth, flows in the channel would spill onto a gently sloping floodplain similar to that found in the Oregon Street Reach.



Figure 7. Existing and design channel profile of Sidney Gulch through the USFS Compound.

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Figure 8. Typical cross section of Sidney Gulch for the channel between Highway 299 and the Ash Hollow Tributary (looking downstream).

The gently sloping floodplain would have variable width up to 11 feet wide and a side slope of 5H:1V. These more gentle side slopes would provide suitable slopes for establishment of riparian vegetation. The upper bank slopes will likely vary depending on the width of the available channel corridor, and may need to be as steep as 2H:1V at the narrowest point in the corridor, but could be more gentle where the available corridor is wider.

Hydraulic Analysis and Summary of Design Geomorphic Characteristics The typical design channel was evaluated using the WinXSPro (USFS, 2005) software to estimate the hydraulic geometry, assess flood frequency associated with design bankfull channel and floodplain, and to analyze sediment transport competence from the 1.1- through the 10-year flow events. A slope of 2.11% was used, and depth-dependent channel roughness values were determined using Limerinos (1970) using the average D84 value from pebble count data collected in the Upstream and Weaver Bally baseline reaches. Computations are show in Attachment 4.

The main channel will convey flow events up to the 1.4-year return period before spilling onto the sloping floodplain. HEC-RAS modeling of proposed design conditions will be necessary to evaluate the actual flood conveyance of the channel corridor.

Table 3 summarizes the geomorphic characteristics of the project reach and typical cross section.

Predicted sediment transport competence of the design cross section is show on Figure 6. Sediment transport competence in the reach falls between the sediment delivery and receiving reaches, thus maintaining sediment transport continuity from upstream, through the project reach, to downstream.

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Table 3. Summary of the geomorphic characteristics of the project reach and typical cross section.

Metric Value Overall Slope 2.11% Planform Sinuosity 1.025 Active Channel Width 10 feet Bankfull Width 15.6 feet Bankfull Depth 1.5 feet Bankfull W/d ratio 13.2 Bankfull Return Period 1.4 years 2-Year Entrenchment Ratio 1.3

Ash Hollow and Garden Gulch Tributaries Lowering the channel elevation of Sidney Gulch necessitated increasing the channel slopes of the Garden Gulch and Ash Hollow tributaries between Highway 299 and their confluences with Sidney Gulch. The proposed slope of Garden Gulch channel profile would be approximately 3% and the Ash Hollow channel profile would be 3.4%. Coarse-bedded plane bed or step-pool channels are most appropriate for channels in this slope range (Montgomery and Buffington, 1997). The width of the available channel corridors for both tributaries are highly constrained by adjacent trees, buildings, and parking areas.

The Garden Gulch Tributary, which has a drainage area similar in size to Sidney Gulch, was designed to provide juvenile salmonid passage up to the Highway 299 crossing using a series of step-pools with 6-in drops between steps. The active channel width of the channel cross section would be 6-feet wide. Due to the space constraints created by utilities and parking areas on both sides of the channel, stacked rock banks with 1H:1V side slopes would be necessary along portions of both sides of the channel. Upstream of Highway 299, the Garden Gulch tributary is substantially aggraded with sediment, which was not evaluated as part of this project.

The preliminary plans for the Ash Hollow tributary propose step-pools with one-foot drops that could limit juvenile passage into the channel except when Sidney Gulch backwaters into the tributary. Rather than step-pools, the final design for the Ash Hollow channel may include a plane-bed channel with large rock features that would better allow juvenile salmonid access into the channel. The active channel width of the channel cross section would be 6-feet wide. Due to the space constraints created by trees and a building adjacent to the channel, stacked rock banks with 1H:1V side slopes would be necessary along portions of both sides of the channel.

The planform alignment of both tributaries were designed to minimize the feasible confluence angle with Sidney Gulch. To facilitate sediment transport continuity and minimize erosion at the tributary confluences, it is recommended that the tributary confluence join with the mainstem at an angle between 15 and 45 degrees (Best, 1988). The confluence angle of Garden Gulch with Sidney Gulch would be approximately 24 degrees. Space constraints at the Garden Gulch confluence limited the confluence angle to approximately 40 degrees.



NEXT STEPS

Items to Consider Watershed History and Sediment Transport Analysis Due to the terrain, geology, wildfires, and land use activities within its watersheds, Sidney Gulch and its tributaries convey a large sediment load. Currently, the undersized crossing at the Weaver Bally Loop is trapping a substantial amount of this sediment on the Sidney Gulch mainstem, potentially creating a supply-limited channel downstream. Once the Weaver Bally Loop crossing is replaced, it can be expected that sediment transport continuity will be re-established and a large amount of sediment could be delivered downstream. Because the actual sediment load is unknown, it is not possible to predict how future changes in sediment loading will affect the project area.

The preliminary hydraulic analysis indicated that the Memorial Drive crossing and Highway 299 crossings are substantially undersized. The flow backwaters during larger events at these crossing could result in these crossings trapping sediment in a similar manner as at the Weaver Bally Loop crossing. With the replacement of the Weaver Bally Loop crossing and re-initiation of sediment transport downstream, backwaters due to the undersized Memorial Drive and Highway 299 crossings may result in sediment aggradation upstream of these crossings. This could result in reduction of crossing capacity, and increase flooding upstream of the crossings, and maintain the sediment deficit downstream.

It is recommended that additional sediment transport analyses be conducted in the channel reaches upstream of the project area that consider both existing conditions and with future crossing replacements at Weaver Bally Loop, Memorial Drive and Highway 299. Optimally, this should include active sediment transport load and size sampling during high flow events that can be used to calibrate a sediment transport capacity model. If this is not feasible, additional pebble counts and bulk samples should be obtained upstream of the project area, and a non-calibrated sediment transport analysis be performed using HEC-RAS and methods presented in Wilcock (2001).

Detailed Deign Development This memorandum presents only a brief analysis of the geomorphology of Sidney Gulch, resulting in the preliminary design of a channel planform, profile and one typical cross section. Additional geomorphic analyses should be conducted on Sidney Gulch as well as the Ash Hollow and Garden Gulch tributaries.

Next steps in the detailed design development should include:

1. Evaluation of retrofit option feasibility to lower the channel bed at the Forest Avenue crossing, 2. Identification of utilities or infrastructure constraints that may limit the channel corridor width

or profile,

3. Development of typical cross sections and evaluation of sediment transport continuity through the project reach, and

4. Evaluation of project impacts on FEMA base-flood elevation.



REFERENCES

ACOE. 1989. Floodplain Management Services Special Study Weaverville Streams Trinity County, California. U.S. Army Corps of Engineers, San Francisco District.

Best, J. L. 1988. Sediment transport and bed morphology at river channel confluences. Sedimentology, 35: 481-498.

CGI Technical Services, Inc. 2014. Draft Geotechnical Report Sidney Gulch Restoration Project Northwest California Resource Conservation and Development Council, Trinity County California.

5C. 2013. Hydraulic Study of Sidney Gulch. Prepared by Five Counties Salmonid Conservation Program.

5C. 2014. Addendum to the Hydraulic Study of Sidney Gulch: Theoretical Channel Modification. Prepared by Five Counties Salmonid Conservation Program.

FEMA, 2010. Flood Insurance Study. Trinity County California and Incorporated Areas. Community Number 060401. Flood Insurance Study Number 06105CV000B.

Gotvald, A.J., Barth, N.A., Veilleux, A.G., and Parrett, Charles, 2012, Methods for determining magnitude and frequency of floods in California, based on data through water year 2006: U.S. Geological Survey Scientific Investigations Report 2012–5113, 38 p.

Limerinos. J. 1970. Determination of the manning coefficient from measured bed roughness in natural channels. Geological Survey Water-Supply Paper 1898-B.

Montgomery, D. and Buffington, J. 1997. Channel-reach morphology in mountain drainage basins. GSA Bulletin, 1.9: 596-611.

NRCS. 2007. Stream Restoration Design. Part 654 National Engineering Handbook. United States Department of Agriculture, National Resources Conservation Service.

Parker, G., Klingeman, P.C., and McLean, D.L. 1982. Bedload and size distribution in paved gravel-bed streams: American Society of Civil Engineers, Proceedings, Journal of the Hydraulics Division, v. 108, p. 544-571.

PRISM. 2000. Parameter-elevation Regressions on Independent Slopes Model. Oregon State University.

USFS. 2005. WinXSPRO, A Channel Cross Section Analyzer, User's Manual, Version 3.0, Gen. Tech. Rep. RMRS-GTR-147. U.S. Department of Agriculture, U.S. Forest Service, Rocky Mountain Research Station, Fort Collins, CO.

USFS. 2008. Stream Simulation: An ecological approach to providing passage for aquatic organisms at road-stream crossings. Forest Service Stream Simulation Working Group, San Dimas, CA.

Waananen, A. O., and Crippen, J.R. 1977. Magnitude and frequency of floods in California, Water Resources Investigation 77-21. Pages 96 in. U. S. Geological Survey, Menlo Park, California.

Wilcock. P.R. 2001. Towards a practical method for estimating sediment-transprot rates in gravel bed rivers. Earth Surface Processes and Landforms. 26: 1395-1408.

Wilcock, P., Pitlick, J. Cui, Y. 2009. Sediment transport primer: estimating bed-material transport in gravel-bed rivers. Gen. Tech. Rep. RMRS-GTR-226. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 78 p.



Wiseman. E. 2010. Spawning Survey Report: Sidney Gulch, Trinity County CA. Trinity United States Forest Service River Management Unit, Shasta-Trinity National Forest.

Wolman, M.G. and Miller, J. 1960. Magnitude and frequency of forces in geomorphic processes. Journal of Geology. 68: 54-74.

ATTACHMENTS

Attachment 1: Existing Condition Base Mapping of Project Area

Attachment 2: Peak Flow Hydrology

Attachment 3: Geomorphic and Hydraulic Analysis of Baseline Reaches

Attachment 4: Geomorphic and Hydraulic Analysis of Design Cross Section

Attachment 5: Preliminary Design Plans



Attachment 1:

Existing Condition Base Mapping of Project Area



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Attachment 2:

Peak Flow Hydrology



Sidney Gulch near Weaverville, CA

North Coast Regional Regression Equations 1

A Drainage Area (mi2)

P Mean Annual Precipitation

(in/yr)

Q-1.1yr(cfs)

Q-1.5yr(cfs)

Q-2yr(cfs)

Q-5yr(cfs)

Q-10yr(cfs)

Q-25yr(cfs)

Q-50yr(cfs)

Q-100yr(cfs)

Sidney Gulch at Upstream Reach 1.576 44.0 40 78 113 225 308 417 501 590

Sidney Gulch at 299 2.562 42.5 60 117 170 338 460 623 749 881

Garden Gulch at 299 2.486 42.0 57 112 163 326 445 603 725 853

Ash Hollow at 299 0.272 39.5 6 14 21 44 61 84 102 121

1 Estimates using regional regression equations developed for the North Coast Region of California by the USGS (Gotvald, Barth, Veilleux, and Parrett, 2012). Q2-yr = 1.82 A0.904 P0.983 Q5-yr = 8.11 A0.887 P0.772

Q10-yr = 14.8 A0.88 P0.696 Q25-yr = 26.0 A0.874 P0.628

Q50-yr = 36.3 A0.87 P0.589 Q100-yr = 48.5 A0.866 P0.556

Mean annual precipitation was obtained from Parameter-elevation Regressions on Independent Slopes Model (PRISM) data set provided by Oregon Climate Service (OCS) mapping program.

Attachment 2 Peak Flow Hydrology

Michael Love & Associates, Inc. 1 of 2

Drainage Area Map of Sidney Gulch and its Tributaries to Highway 299 in Weaverville, CA

Attachment 2 Peak Flow Hydrology


Attachment 3:

Geomorphic and Hydraulic Analysis of Baseline Reaches



Sidney Gulch Upstream Reach Field Data

Upstream Reach Riffle Slopes

StaActive Channel

Width (ft) Bankfull Width (ft) Valley Width (ft) Notes Bankfull Depths (ft) Sta (ft) Th Elev (ft) WS Elev TW slope WS Slope70 6.0 12.0 60 Riffle in Delta Min 1.13

122 7.5 12.6 80Crest Riffle upstream

end of delta Max 2.39 386 99.63 99.95 2.3% 3.0%150 6.7 11.3 72 Riffle toe Average 1.57 375 99.38 3.3%177 7.4 12.5 107 XS1 Median 1.55 352 98.61 98.93 1.5% 1.7%214 7.0 10.4 107 314 98.05 98.3 2.7% 2.1%257 7.4 10.6 107 step in riffle 279 97.11 97.58 2.4% 2.7%307 7.4 10.0 75 XS2, toe riffle 216 95.59 95.89 1.5% 1.7%Min 6.0 10.0 60.0 172 94.95 95.16 1.6% 1.8%Max 7.5 12.6 107.0 113 94 94.07

Average 7.1 11.3 86.9Median 7.4 11.3 80.0 Average 2.18% 2.15%

Overall 2.06% 2.15%Downstream Weaver Bally ‐ Location at Pebble Count 2 Median 2.27% 1.95%

Active Channel Width (ft) Bankfull Width (ft)

Top of Bank Width (ft)

Min. Top of Bank Height (ft) Overall (1+13 to 1.93% 2.03%

6.6 10.5 4.56.0 9.0 68.7 16.0 89.0 15.5 22.0 6

Min 6.0 9.0Max 9.0 16.0Average 7.6 12.8Median 7.6 13.0

91

92

93

94

95

96

97

98

99

100

101

102

50 100 150 200 250 300 350 400

Elevation (ft), A

rbitrary Datum

Station (ft)

Sidney Gulch Upstream Reach

Thalweg (ft)

Water Surface (ft)

Bankfull Indicators (ft)

Riffle Slopes

WS Slope

Linear (Bankfull Indicators (ft))

Attachment 3 Baseline Geomorphic Data


Watershed Location

Sidney Gulch at Upstream Reach Slope 2.10%Hydraulic Resistance (n) Using Limerinos (1970)

Return Period (yr)

Flow (cfs) Location Return Period

Flow (cfs)

Max. Depth (ft)

Top Width, W (ft) Area (SF) Shear (psf)

Avg depth, d (ft)

Velocity (fps) n W/d

D50 Moved (mm) R/D84

1.1 40 Field Bankfull 1.14 44 1.2 12.2 10.3 1.1 0.8 4.3 0.044 14.5 78 2.7431.5 78 Field Floodplain 7.80 271 2.7 26.0 38.5 1.9 1.5 7.1 0.039 17.5 138 4.8432 113 Upper Floodplain 20.59 385 3.2 39.1 55.9 1.8 1.4 6.9 0.039 27.3 135 4.7075 225 1.1-yr 1.14 44 1.2 12.2 10.3 1.1 0.8 4.3 0.044 14.5 78 2.743

10 308 1.5-yr 1.51 79 1.6 16.5 16.1 1.2 1.0 4.9 0.042 16.8 92 3.18325 417 2-yr 2.17 119 1.9 18.9 21.4 1.4 1.1 5.6 0.041 16.7 106 3.69150 501 5-yr 4.80 218 2.4 21.9 31.6 1.8 1.4 6.9 0.039 15.2 135 4.707

100 590 10-yr 7.92 274 2.9 35.9 44.7 1.6 1.3 6.1 0.040 28.7 118 4.098

95

95

96

96

97

97

98

98

99

99

40 50 60 70 80 90 100 110 120

Elev

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n (ft

)

Station (ft)

Cross Section

Upper Floodplain

Field Floodplain

Field Bankfull

1.1-yr WSE

Upstream Reach - Section 1



Watershed Location

Sidney Gulch at Upstream Reach Slope 2.10%Hydraulic Resistance (n) Using Limerinos (1970)

Return Period (yr)


Flow (cfs)

Max. Depth (ft)


Avg depth, d (ft)



1.1 40 Field bankfull (RT) 1.25 55 1.4 10.3 10.7 1.3 1.1 5.1 0.042 9.8 95 3.3191.5 78 Field bankfull (LT) 1.38 67 1.6 12.2 12.9 1.3 1.1 5.2 0.042 11.5 97 3.3872 113 Floodplain 2.38 127 2.3 23.1 24.3 1.3 1.1 5.2 0.042 21.8 98 3.4215 225 1.1-yr 1.17 47 1.3 10.0 9.7 1.2 1.0 4.8 0.043 10.2 89 3.11610 308 1.5-yr 1.54 81 1.8 15.0 15.7 1.3 1.1 5.1 0.042 14.3 96 3.35325 417 2-yr 2.10 117 2.1 17.6 20.6 1.5 1.2 5.7 0.041 15.0 108 3.75950 501 5-yr 4.96 223 2.8 43.9 43.9 1.3 1.0 5.1 0.042 43.9 95 3.319

100 590 10-yr 9.95 307 3.0 45.3 52.9 1.5 1.2 5.8 0.041 38.7 110 3.861

97

98

99

100

101

102

103

0 10 20 30 40 50 60 70 80

Ele

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n (ft

)

Station (ft)

Upstream Reach - Section 2

Cross Section

Floodplain

Field bankfull (LT)

Field bankfull (RT)

1.1-yr WSE



Watershed LocationSidney Gulch at 299

Slope 1.65%Return

Period (yr)Flow (cfs) Hydraulic Resistance (n) Using Limerinos (1970)

1.1 60 LocationReturn Period

Flow (cfs)

Max. Depth (ft)


Avg depth, d (ft)



1.5 117 Upper Floodplain 8.25 417.6 4.3 17.9 46.2 2.3 2.6 9.0 0.036 6.9 170 7.5862 170 Field Floodplain 4.74 323 3.7 14.7 36.8 2.2 2.5 8.8 0.036 5.9 164 7.3155 338 1.1-yr 1.11 62 1.8 10.8 12.6 1.1 1.2 4.9 0.041 9.3 82 3.658

10 460 1.5-yr 1.56 124 2.4 12.0 19.4 1.5 1.6 6.4 0.039 7.5 111 4.94525 623 2-yr 2.10 175 2.8 12.9 24.4 1.7 1.9 7.2 0.038 6.8 129 5.72350 749 5-yr 5.18 342 3.8 14.9 38.3 2.3 2.6 8.9 0.036 5.8 168 7.485

100 881 10-yr 9.99 460 4.6 21.0 52.1 2.2 2.5 8.8 0.036 8.5 166 7.383

2080

2081

2082

2083

2084

2085

2086

2087

2088

2089

2090

0 10 20 30 40 50 60 70 80 90 100

Ele

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n (ft

)

Station (ft)

Weaver Bally Station 65+96

Cross Section

Upper Floodplain

Field Floodplain

1.1-yr WSE



Watershed LocationSidney Gulch at 299 Slope 1.65%

Hydraulic Resistance (n) Using Limerinos (1970)

Return Period (yr)


Flow (cfs)

Max. Depth (ft)


Avg depth, d (ft)



1.1 60 1.5 117 Field Floodplain 3.10 231 3.0 21.7 35.1 1.6 1.6 6.6 0.038 13.4 116 5.1482 170 Field Bankfull 1.76 145 2.4 16.0 23.7 1.4 1.5 6.1 0.039 10.7 106 4.7075 338 1.1-yr 1.10 61 1.6 11.6 12.8 1.1 1.1 4.8 0.041 10.4 79 3.52210 460 1.5-yr 1.53 120 2.2 14.7 20.7 1.4 1.4 5.8 0.039 10.5 100 4.43725 623 2-yr 1.98 168 2.6 18.0 27.1 1.5 1.5 6.2 0.039 11.9 108 4.77550 749 5-yr 4.95 335 3.4 22.7 44.0 1.9 1.9 7.6 0.037 11.7 138 6.130

100 881 10-yr 9.79 455 3.8 23.6 53.3 2.2 2.3 8.5 0.037 10.4 159 7.078

2076

2078

2080

2082

2084

2086

0 5 10 15 20 25 30 35 40 45 50

Ele

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n (ft

)

Station (ft)

Weaver Bally Station 63+88

Cross Section

Field Floodplain

Field Bankfull

1.1-yr WSE



Watershed LocationSidney Gulch DS Garden/Forest

Slope 1.67%Return


1.1 124 Location Return PeriodFlow (cfs)

Max. Depth (ft)


Avg depth, d (ft)



1.5 243 Field Back of Bar 4.88 693 4.7 26.1 70.4 2.6 2.7 9.9 0.036 9.7 191 8.3992 354 Field Front of Bar 1.50 244 3.0 17.6 32.8 1.8 1.9 7.4 0.038 9.4 135 5.9275 707 1.1-yr 1.13 131 2.3 14.7 21.5 1.4 1.5 6.1 0.039 10.1 107 4.674

10 966 1.5-yr 1.50 244 3.0 17.6 32.8 1.8 1.9 7.4 0.038 9.4 135 5.92725 1,310 2-yr 2.08 364 3.6 21.0 44.4 2.1 2.1 8.2 0.037 10.0 152 6.67250 1,576 5-yr 4.73 693 4.7 26.1 70.4 2.6 2.7 9.9 0.036 9.7 191 8.399100 1,855 10-yr 9.56 943 5.3 27.8 86.6 2.9 3.1 10.9 0.035 8.9 218 9.550

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

0 10 20 30 40 50 60

Elev

atio

n (ft

)

Station (ft)

Oregon Station 26+12

Cross Section

Field Back of Bar

Field Front of Bar

1.1-yr WSE



Watershed LocationSidney Gulch DS Garden/Forest

Slope 1.67%Return



Max. Depth (ft)


Avg depth, d (ft)



1.5 243 Field Floodplain 1.68 283 3 23.0 40.1 1.7 1.8 7.1 0.038 13.1 127 5.5542 354 Field Bankfull 1.09 120 2 15.1 20.8 1.3 1.4 5.8 0.040 11.1 99 4.3695 707 1.1-yr 1.12 130 2.1 16.0 22.3 1.4 1.4 5.8 0.039 11.4 101 4.437

10 966 1.5-yr 1.48 239 2.8 21.8 35.7 1.6 1.6 6.7 0.038 13.3 119 5.21525 1,310 2-yr 2.04 359 3.3 24.9 47.3 1.9 1.9 7.6 0.037 13.1 138 6.06250 1,576 5-yr 4.98 705 4.3 29.8 74.9 2.4 2.5 9.4 0.036 11.9 181 7.925100 1,855 10-yr 9.48 939.2 4.8 31.5 90.2 2.8 2.9 10.4 0.036 11.0 205 9.009

2000

2002

2004

2006

2008

2010

2012

2014

2016

0 10 20 30 40 50 60

Ele

vatio

n (ft

)

Station (ft)

Oregon Station 25+72

Cross Section

Field Floodplain

Field Bankfull

1.1-yr WSE



WinXSPRO Results Upstream Reach Section 1

Pebble Count Info.

D84 0.30 ft

D50 0.11 ft

Slope = 0.021 ft/ft

Limerinos Eqn

STAGE Section AREA PERIM WIDTH R DHYD SLOPE R/D84 n V Q q EDF

(ft) (T=Total) (sq ft) (ft) (ft) (ft) (ft) (ft/ft)

0.9-69 (most >2

MLA)(0.02

WinXSPRO Results Upstream Reach Section 2

Pebble Count Info.

D84 0.30 ftD50 0.11 ft

Slope = 0.021 ft/ft

Limerinos Eqn



0.9-69 (most >2

MLA)(0.02

WinXSPRO Results Weaver Bally Sta. 65+96

Pebble Count Info.

D84 0.30 ft

D50 0.11 ft

Slope = 0.017 ft/ft

Limerinos Eqn



0.9-69 (most >2

MLA)(0.02



0.9-69 (most >2

MLA)(0.02

WinXSPRO Results Weaver Bally Sta. 63+88

Pebble Count Info.

D84 0.30 ft

D50 0.11 ft

Slope = 0.017 ft/ft

Limerinos Eqn



0.9-69 (most >2

MLA)(0.02



0.9-69 (most >2

MLA)(0.02

WinXSPRO Results Oregon Sta. 26+12

Pebble Count Info.

D84 0.30 ft

D50 0.11 ft

Slope = 0.017 ft/ft

Limerinos EqnSTAGE Section AREA PERIM WIDTH R DHYD SLOPE R/D84 n V Q q EDF

(ft) (T=Total) (sq ft) (ft) (ft) (ft) (ft) (ft/ft)0.9-69 (most >2

MLA)(0.02


(ft) (T=Total) (sq ft) (ft) (ft) (ft) (ft) (ft/ft)0.9-69 (most >2

MLA)(0.02

WinXSPRO Results Oregon Sta. 25+72

Pebble Count Info.

D84 0.30 ft

D50 0.11 ft

Slope = 0.0167 ft/ft

Limerinos Eqn



0.9-69 (most >2

MLA)(0.02



0.9-69 (most >2

MLA)(0.02

Attachment 4:

Geomorphic and Hydraulic Analysis of Design Cross Section



Watershed LocationSidney Gulch DS 299 Slope 2.11%

Return Period

(yr) Flow (cfs) Hydraulic Resistance (n) Using Limerinos (1970)


Max. Depth (ft)


Avg depth, d (ft)



1.5 117 Slope Break 1.43 106.6 1.5 15.6 18.4 1.5 1.2 5.8 0.041 13.2 110 3.8272 170 1.1-yr 1.07 57 1.1 14.0 12.5 1.1 0.9 4.5 0.043 15.7 84 2.9135 338 1.5-yr 1.52 119 1.6 16.5 20.1 1.5 1.2 6.0 0.040 13.6 113 3.96210 460 2-yr 2.18 180 2.0 20.1 27.4 1.7 1.4 6.6 0.039 14.8 127 4.43725 623 5-yr 5.12 341 2.7 26.1 43.6 2.1 1.7 7.8 0.038 15.6 158 5.45350 749 10-yr 8.98 435 3.0 28.5 51.8 2.3 1.8 8.4 0.038 15.6 171 5.961

100 881 Aprox. 3 yr 3.24 239 2.3 22.8 33.8 1.9 1.5 7.1 0.039 15.4 139 4.843100-Year 84.49 840 3.9 32.9 79.7 3.1 2.4 10.5 0.036 13.5 226 7.891

2075

2076

2077

2078

2079

2080

2081

110 115 120 125 130 135 140 145 150 155 160E

leva

tion

(ft)

Station (ft)

Typical Design Cross Section Between Hwy 299 and Ash Hollow Tributary

Cross Section

100-Year

Slope Break

5-yr

1.1 year

Attachment 4 Geomorphic and Hydraulic Analysis of Design Cross Section


WinXSPRO Results Design Cross Section Hwy 299 to Ash Hollow

Pebble Count Info.D84 0.30 ftD50 0.11 ft

Slope = 0.021 ft/ft

Limerinos Eqn



0.9-69 (most >2

MLA)(0.02

Attachment 5:

Preliminary Design Plans



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PREPARED FOR:

FIVE COUNTIES SALMONID CONSERVATION PROGRAM

NORTHWEST CALIFORNIA RESOURCE CONSERVATION & DEVELOPMENT COUNCIL

USFS COMPOUND SITE FEASIBILITY STUDY (GRANT SGFS1)

TRINITYCOUNTY

SIDN

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SHEET INDEX

Sheet No. DESCRIPTION

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Technical MemorandumMemoraNdum PurposeIntroductionBackgroundProject Goals and ObjectivesPrevious Work in the Project AreaTopographic SurveyHEC-RAS Hydraulic AnalysesGeotechnical Assessment

Project ApproachPeak Flow Hydrology

Geomorphic EvaluationOverviewGeomorphology of Baseline ReachesUpstream ReachWeaver Bally ReachOregon Street Reach

Hydraulic Geometry Analysis of Baseline ReachesSediment Transport Analysis of Baseline Reaches

Preliminary DesignConstraintsSidney GulchDesign ObjectivesPlanformProfileCross SectionHydraulic Analysis and Summary of Design Geomorphic Characteristics

Ash Hollow and Garden Gulch Tributaries

Next StepsItems to ConsiderWatershed History and Sediment Transport Analysis

Detailed Deign Development

ReferencesAttachmentsAttachment 1 Sidney Gulch at USFS Compound Base Map.pdf2_SID_E-BASE-MAP-OVERVIEW-Overview2_SID_E-BASE-MAP-DETAIL-Layout12_SID_E-BASE-MAP-DETAIL-Layout 2

draft technical memorandum5counties.org/docs/projects/sgfs1_geomoprh_tm.pdf · sidney gulch and its...

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