islais creek sediment source assessmentonline.sfsu.edu/jerry/geo_642/studentprojects/2007/glen...

Watershed Assessment and Restoration GEOG 642 - Fall 2007

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Islais Creek Sediment Source Assessment: Glen Canyon Park, San Francisco

December 2007

Prepared by

Dylan Duvergé Alicia Omlid Silas Toms Diana Hull


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TABLE OF CONTENTS 1. INTRODUCTION .......................................................................................................... 3

1.1 General Location and Description ............................................................................ 3 1.2 Problem Statement and Project Purpose ................................................................... 3 1.3 Stakeholders and Existing Projects ........................................................................... 5

2. ENVIRONMENTAL SETTING .................................................................................... 8 2.1 Geologic Setting ........................................................................................................ 8 2.2 Hydrologic Setting .................................................................................................. 11 2.3 History & Land Use Setting .................................................................................... 16

3. METHODS ................................................................................................................... 17 3.1 Data Sources ........................................................................................................... 17

3.1.1 San Francisco Digital Database (SFDDB) ....................................................... 17 3.1.2 San Francisco Parks and Recreation Department ............................................ 17

3.2 Survey Methods ...................................................................................................... 18 4. RESULTS ..................................................................................................................... 20

4.1 Initial Site Assessment ............................................................................................ 20 4.2 Mapping of Impervious Surfaces ............................................................................ 23 4.3 Mapping of Lower Stream Reach ........................................................................... 24

5. DISCUSSION & RECOMMENDATIONS ................................................................. 26 6. REFERENCES ............................................................................................................. 29

FIGURES Figure 1 - Sediment Accumulation Under Pedestrian Bridge ............................................ 4 Figure 2 - San Francisco's Significant Natural Areas ......................................................... 7 Figure 3 - Geologic Map of Glen Canyon ........................................................................ 10 Figure 4 - USGS Landslide Hazard Zones ....................................................................... 11 Figure 5 - Islais Creek Watershed (shown in blue) ........................................................... 12 Figure 6 - Historic creeks and wetlands of San Francisco.. .............................................. 13 Figure 7 – GIS Map of Historic Versus Urban Watershed Area ...................................... 15 Figure 8 - Field Sketch of Lower Stream Reach............................................................... 22 Figure 9 - Longitudinal Profile of Lower Islais Creek Reach.. ........................................ 25 Figure 10 - Map view of lower stream reach survey. ....................................................... 26

1. INTRODUCTION

1.1 General Location and Description Glen Canyon Park is an approximately 70 acre park located in the city of San

Francisco to the south and east of the topographically highest points in the city, including

Twin Peaks and Mount Davison. The park is located between the low-density residential

neighborhoods of Twin Peaks, Diamond Heights, Mira Loma and Glen Park. It is

bounded on the north side by Portola Dr. and the School of the Arts; on the east and south

sides by O’Shaughnessy Dr. and Bosworth St.; and on the west side by residential

development and the Diamond Heights Shopping Center. It is a deeply carved canyon

with moderate to extremely steep slopes on each side. Elevations range from 230 feet on

the south end to 575 feet on the north rim of the canyon.

Glen Canyon Park can be accessed from Bosworth St., Elk St., the end of Sussex

Dr., and Christopher Park Playground. Several unplanned access points exist as well,

including access from O’Shaughnessy Blvd., School of the Arts and residential homes on

the east side of the canyon. The park is home to a large graded sports and recreation field

at its readily accessible south end, including a baseball diamond, a gymnasium, picnic

area, and a children’s playground. In addition, a building further north of the recreational

field houses the Silver Tree Day Camp. The natural area of the park is accessed with a

variety of trails and is used for walking, running, hiking, dog-walking; bird watching and

general enjoyment of the scenery.

1.2 Problem Statement and Project Purpose Islais Creek, which flows through the bottom of the canyon, represents one of the

last free flowing creeks in the city of San Francisco. For this reason alone, it is a

significant resource that should be protected and enhanced. Because of a drastic

reduction in watershed size due to urbanization (see section 2), the stream has suffered a

significant reduction in flow, leading to difficulties in mobilizing even the finest of

sediments. The park has over 23,000 feet of planned trails, and at least 3,700 feet of

unplanned, “social” trails, all of which are popular with area residents for short hikes (SF

Parks and Rec, 2006). Unfortunately, many of these trails contribute to erosion when


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they channel runoff that would normally drain away as sheet flow. Reduction in stream

flow, upland soil disturbances from park visitors, erosion, and encroachment of riparian

vegetation have caused the stream to be choked with fine sediments and organic matter.

Excessive sediment loading is a problem for several reasons. Firstly, the capacity

of Islais Creek to handle peak flows is reduced, leading to the potential for floods during

heavy rains. This is an issue throughout the course of the stream, but may be especially

problematic where old culverts have filled over halfway with fine sediments (Figure 1).

Additionally, many riparian plants and animals depend on open water pools and riffles to

thrive. While there are not any fish in Islais Creek, it is home to many invertebrates, such

as forktail damselflies, and several species of reptiles and amphibians (Parks and Rec,

2006). Finally, flow reduction and aggressiveness of native plant species has caused

vegetation to encroach on the stream channel and reduce penetration of sunlight. A

successful native habitat requires open areas of sunlight that allow access to the stream

for birds and insects, and provide favorable conditions for native riparian vegetation.

Figure 1 - Sediment Accumulation Under Pedestrian Bridge

This study aimed to map areas with impervious surfaces and investigate

connections between the stream system and areas where runoff from canyon walls

channel eroded sediments. In addition, a site reconnaissance was performed to locate and

evaluate current conditions and erosion control measures. A stream reach survey was


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conducted on a restored portion of the stream to provide baseline data against which to

compare future studies. Because existing efforts to restore the stream and address the

aforementioned issues have are already occurred in some areas (section 1.3), this report

aims to assess the effectiveness of these efforts, and determine whether future plans are

appropriate in light of our evaluation. Any measures to reduce sedimentation in the

stream that are not occurring or planned will be recommended at the end of this report.

1.3 Stakeholders and Existing Projects There are many groups with a vested interest in Glen Canyon Park. The San

Francisco Parks and Recreations Department has the main operational control over the

park, but there are a large number of other interest groups that exert influence on

decisions related to the park. They include the Neighborhood Parks Council, Glen Park

Neighborhood Association, Friends of Glen Park, Friends of Islais Creek, School of the

Arts, and city residents that make use of the park and attend community meetings.

One of the primary conflicts between stakeholders revolves around the use of the

park as a recreational resource versus the preservation and restoration of the park as a

valuable natural habitat and riparian system. Many residents view the preservation and

restoration of the canyon environment as restricting their access, and any serious efforts

to restore park habitats would indeed require park users to remain on designated paths.

Part of the appeal of Glen Canyon Park is in the fact it is wild and open, and this attracts

uses that conflict with environmental goals, such as off-leash dog walking, rock climbing

and off trail exploring. However, surveys conducted at community meetings have

generally shown a favorable opinion for stream restoration, removal of invasive species,

and erosion/sediment controls.

The Natural Areas Program (SFNAP) of the San Francisco Parks and Recreation

Department (SF Parks and Recreation) and Friends of Glen Canyon Park have recently

been active in efforts to restore native habitat, eliminate invasive species, and address

erosion and sedimentation issues. In 1995, SF Parks and Recreation designated Glen

Canyon Park one of the city’s Significant Natural Resource Areas, which helped provide

the impetus and the funds to carry out various habitat restoration, trail maintenance and


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stream improvement projects (figure 1). Since 2004, several projects have been

implemented, including:

• Removal of 21 eucalyptus trees

• Installation of straw wattles on hillside channels and creek-bank gullies

• Gravel filling of eroded portions of main access road

• Placement of water bars to direct runoff into creek at regular intervals on main

access road. Serves to reduce magnitude and velocity of channelized flow

• Installation of creek channel structures to concentrate stream flow and pond water

• Removal of invasive plant species and planting of native vegetation along lower

creek reach.

Most of these project have been implemented on the lower stream reach, just

north of the culverted section of the creek. In 2006, SF Parks and Rec released the

Significant Natural Resource Areas Management Plan, which outlined the issues related

to mainting the park as a natural resource, and recommended actions to address the

problems. While most of the report focused on habitat management and wildlife, because

the stream is such an important habitat, there was some discussion of stream restoration

and sediment accumulation issues.


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Figure 2 - San Francisco's Significant Natural Areas

Friends of Glen Canyon, an active citizen volunteer group meets once a month in

Glen Canyon to remove exotics, plant native species, and thin willow overgrowth. In on-

site assessments in the fall of 2007, the group noted several continuing problems and

complains related to park improvements. They are as follows:

• The vegetation removal/installation is progressing very slowly

• Regular trail maintenance is lacking

• There are numerous cut slope “social trails” trails that have been “closed” by

staking of hay waddles across, these are failing and rill development continues.

• Rills and/or gullies exist near every wooden step and stair that compensates for

elevation change.


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• People allow their dogs to run freely into the creek.

• The creek is extremely sluggish or doesn’t run at all and its bed is composed of

humus and fine particles. It has the appearance of a colluvial hollow in some

places and a muddy bog in others.

Many of these observations are consistent with our own assessment discussed in section

4.1.

2. ENVIRONMENTAL SETTING

2.1 Geologic Setting The City of San Francisco is located within the Coast Ranges geomorphic

province. The geology can generally be described as bedrock hills surrounded by broad

valleys, which are underlain by unconsolidated deposits or artificial fill. The bedrock

comprises sedimentary and metamorphic rocks of the Franciscan formation, late Jurassic

or Cretaceous in age. The unconsolidated surficial deposits are of the Pleistocene and

Holocene age, and are the result of wind- or water-deposited sand, mud, and clay; slope

wash; alluvium; landslide debris; and artificial fill. The thickness of the surficial deposits

range from several feet to more than 100 feet in different places.

As seen in figure 3, the bedrock in Glen Canyon consists of areas of Franciscan

chert, metachert and sandstone. Note that the geology layer in figure 3 is offset by 30 to

50 meters to the northwest from the satellite image. The rocks are marine formations that

were deposited in the Mesozoic period and subsequently accreted onto the continental

margin as the Farallon Plate subducted underneath the North American Plate. Under

such active tectonic regimes, these rocks were tightly folded and in some places

metamorphosed. Over time, these rocks were uplifted to form the topographic heights of

much of San Francisco.

Outcrops of chert and metachert are readily observable in the canyon. Many of

these outcrops are resistant knobs of metamorphosed chert, while in other places they

have well bedded, highly folded chert layers that are 2-5 inches think separated by very

thin units of shale. Franciscan chert is often grayish red to reddish brown in color, while

Franciscan sandstone is grey but is rarely seen in outcrop because it weather more readily


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than chert (Jennings and Burnet, 1961). In some areas, rock climbing by park visitors

have caused soil compaction around the outcrops and has loosened enough fragments of

rock to cause accumulation of rubble at the bases of the rock.

Most of the observable landscape of Glen Canyon, however, consists of

quaternary slope colluvium, thin soils, old landslide deposits and artificial fill. While the

bedrock consists of strong and resistant rocks, the slope of the canyon walls are

extremely steep in places (slopes can approach 100%), and where the dip of sedimentary

layers are out of slope, potential for landslides increase. In fact, the California Geologic

Survey has designated much of Glen Canyon as being at risk for earthquake induced

landslides (figure 4). As part of their assessment, CGS compiled information on existing

landslide deposits, and mapped several in Glen Canyon (California Geologic Survey,

2000). One area had the geomorphic expression of an old landslide, with a steep head

scarp and an anonymously flat hummocky terrain below it out of which water seeps.

Besides landslide deposits, most of the bedrock in the park is overlain by colluvium and

thin, rubbly soils


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Figure 3 - Geologic Map of Glen Canyon


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Figure 4 - USGS Landslide Hazard Zones

2.2 Hydrologic Setting The San Francisco Bay region is under a Mediterranean climate regime, which

means that most of its rainfall is received in the winter months. Many of the streams in

the bay area run dry in the fall. However, at the time of our visit, there was still water in

the creek, if even just a trickle. According to NOAA records, this part of San Francisco

receives an average of 22-24 inches of rain per year. In times when the city wasn’t paved

over, several creeks ran through the watershed as shown in figure 6, but the creek flowing

through Glen Canyon is the last that remains.

The Islais Creek watershed, as seen in figure 5, encompasses a large section of

San Francisco. Our study area focuses on the portion of the watershed above where a

Glen Canyon Area


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culvert brings the stream underground to be drained into the bay. In general, the streams

in watersheds are fed both by surface runoff and groundwater. Surface runoff occurs

mostly in the winter and spring months as a result of direct precipitation, whereas

groundwater is much slower to respond to water recharge, and can sustain flows in

streams all year round. The Department of Water Resources estimates that the Islias

Creek watershed has a surface area of 5930 acres and an estimated annual groundwater

recharge of 1836 Acre-Feet/Year.

Figure 5 - Islais Creek Watershed (shown in blue)

In general, the rocks in the watershed for our study area (shown in figure 7) are

not considered to be formations that are particularly water bearing. In comparison to

alluvial deposits that occur nearer to the bay, rocks of the Franciscan Complex are

impermeable, and groundwater penetrates them only through secondary porosity from

fractures. However, water that does enter Franciscan formations moves slowly along

fractures and any more permeable interbeds. Because of the complex nature of the folded

and faulted rock in the watershed, predicting groundwater depth, magnitude and flow is


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difficult, if not impossible. However, the well yield of a municipal well in the watershed

reported a depth to water of about 100-140 feet.

Figure 6 - Historic creeks and wetlands of San Francisco. Present day artificial fill shown in pink.

Historically, the size of the watershed feeding Islais Creek in Glen Canyon was

much larger, and most likely provided the creek with higher stream flows. The SF Parks

and Recreation reported that the watershed size has had an 80% reduction in area, which

is consistent with a GIS analysis performed and shown in figure 7. According to

watershed and terrain analysis on a 4 square meter digital elevation model, the size of the

natural watershed above the culvert is 282 acres, whereas the size of the urban watershed

is 61 acres. This corresponds to an approximately 78% reduction in watershed area.

Glen Canyon


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Naturally, such a reduction will significantly decrease stream power and reduce the

ability of the stream to mobilize sediment. For this reason, the substrate of the stream

currently consists of silt, mud and organic debris. It was reported that the average slope

of the stream in Glen Canyon is 3% and that the peak flow for a 1.5 year event is 247

cubic feet per second (Jenks and Loenardson. 2004).

According to the Department of Water Resources, the groundwater quality of the

Islais Creek basin passes guidelines set by the EPA. However, the water is considered

hard, and can contain elevated nitrate levels. The surface water is most likely impacted

by excess organic matter. San Francisco's Regional Water Quality Control Board Surface

Water Ambient Monitoring Program has conducted water sampling near the Silver Tree

Day Camp, but because our study focuses on erosion and sedimentation, a long

discussion of water quality is not needed.


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Figure 7 – GIS Map of Historic Versus Urban Watershed Area


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2.3 History & Land Use Setting Glen Canyon Park has an interesting historical background and land use setting.

O’Shaughnessy Boulevard runs along the west side of the park and provides a small,

often unnoticed entry point to the park. The west side is dominated by Blue Gum

Eucalyptus trees, planted by Adolf Sutro, and a dense underbrush, so access on the west

side is restricted to the aforementioned small entry point. The east side is bordered by the

Diamond Heights residential neighborhood and a small shopping center (Diamond

Heights Shopping Center), from which the park can be accessed. The other significant

access point is in the southeast corner on Sussex Street. Many residents have provided

their own access points to the park on the east side as well.

According to the San Francisco Recreation & Parks’ Natural Areas Program, Glen

Canyon was historically part of the hunting territory of the local Ohlone indigenous

tribes. During the late 1700s, Glen Canyon was used as grazing land for the longhorn

cattle and sheep of Mission Dolores.

Under Mexican rule from the 1820s to the 1850s, grazing practices continued. In

the early American times, cattle rustlers and smugglers used the rocky outcrops of

Devil’s Cave and Dead Man’s Cave as hideouts.

The Canyon has never been developed, although there was talk of converting it

into residential land after Crocker Real Estate Company bought the Canyon in 1889.

Crocker even built a mini-amusement park, zoo, aviary, and bowling alley on the

property to attract homebuyers. Just prior to this potential land use shift, the Canyon

housed Giant Powder Company, the country’s first commercial dynamite manufacturing

plant. Crocker Real Estate Company eventually sold the Canyon, then known as the Glen

Park Picnic Grounds, to the City and County of San Francisco in 1922 for $30,000

(SFNPC).

In 1941, O'Shaughnessy Boulevard was built, which reduced the size of the Islais

Creek watershed. The Silver Tree Day Camp, a children’s summer camp, was also

founded in 1941 and the accompanying aforementioned Silver Tree building within the

Park was built in 1956. In the 1970s, a citizens group known as the “Gum Tree Ladies”

formed in order to save Glen Canyon from development. They fought a plan to widen


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O’Shaughnessy Boulevard, which would have made it part of the freeway system, and

would have further degraded the watershed.

More recently, the Canyon was designated a “significant” natural resource by the

Recreation and Park Department in 1995. Today, Glen Canyon Park, The Friends of

Glen Canyon Park, and the Glen Park Association currently aim to restore its natural

areas as well as maintain and upgrade recreational fields and buildings.

3. METHODS

3.1 Data Sources

3.1.1 San Francisco Digital Database (SFDDB) The SFDDB was developed by the San Francisco State Geography Department,

and holds a variety of information. At its current state SFDDB holds information on San

Francisco County as digital geospatial datasets readily compatible with a GIS system,

including Research Systems Research Institute (ESRI) developed software like ArcGIS.

The dataset includes information on the cultural and physical geography of the area.

The available data comes from a variety of sources, including the U.S. Geological

Survey (USGS), NOAA/National Ocean Service (NOS), U.S. Census Bureau, California

Department of Fish and Game, California Department of Forestry and Fire Protection,

California Geological Survey, California Spatial Information Library (CaSIL) and the

City and County of San Francisco Department of Public Works.

Data used for this project include quarter-meter digital orthophotos of San

Francisco; 5-foot elevation contour data; surficial and bedrock geology; land use and

soils.

3.1.2 San Francisco Parks and Recreation Department As the main agency governing the recreational use of Glen Canyon Park, the San

Francisco Parks and Recreation Department aims to actively maintain the recreational

value of the park, while protecting the area’s significant natural resources, including

Islais Creek. One valuable source of information used for this project was the agency’s

city-wide Significant Natural Areas Resource Management Plan (2006). The document


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outlines site-specific issues and management recommendations, and provides a wealth of

factual information on the park. In addition, it describes challenges related to restoring

and maintaining the “naturalistic” state of Islais Creek.

Information used for this project includes maps of park trails, vegetation, and a

list of issues related to erosion, sedimentation and creek habitat enhancement.

3.2 Survey Methods The data collection consisted of GPS readings of visible trails within the

boundaries of the park. Also collected were significant features such as sewer access

caps, storm drains, culverts and water diversion channels. Large trail areas of impervious

concrete or hard packed dirt adjacent to Islais Creek were also digitized. Connectivity to

the creek itself was a central feature of assessment, as the effects of trail use on sediment

yield within the creek were main consideration points. Slope degree and trail width were

also recorded to help assess trails of significance to water movement and sediment

movement.

A data dictionary was created using the Data Dictionary Editor (Appendix X) to

allow for quick field assessments of trail width, condition and slope. The data dictionary

also allowed the user to mark if connectivity to the creek was obvious, if the trail was

paved or not, and if it was obviously a planned or unplanned trail. Other features were

included in the data dictionary to allow for the creation of a polygon shape recording trail

area for the largest trails or recording of other significant areas. A space for notable

feature was also included to allow for any possibility that was not accounted for upon

creating of the data dictionary.

Six visits to Glen Canyon were performed over a period of one month. A culvert

in the middle of the park is where Islais Creek is diverted underground. This culvert was

recorded as a pour point and the watershed was defined as all places “above” that point,

up to the streets that surround the canyon on all sides. All trails within that area were

scouted and mapped using a Trimble Recon 2005 GPS data rover with a Pro XH receiver

attached for increased accuracy. A Leica laser rangefinder was briefly employed to map

point features unreachable by foot; this was less than necessary and was left in disuse

after the initial survey.


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Because the trails were contained within the confines of the Canyon accurate

position data was necessary for analysis. To ensure that position data was very accurate

the Position Dilution of Precision (PDOP) was monitored closely. This adjustable setting

allows the user to set the maximum data collection PDOP between a range of 2-12 (units

are unknown and represent a ordinal range), with 6 being an accepted combination of

precision and productivity. A PDOP of 3 is very accurate and assurance can be taken that

the data is valid; a PDOP of 9 is of lesser value. In the interest of collecting the basic

shape of the features recorded within an acceptable timeframe the PDOP was allowed to

go above 6 if there were limited numbers of satellites granting position data was limited.

When collecting within wooden and brushy areas next to the creek there was also

adjustments made to the PDOP to ensure a recording, precision then being an

afterthought to completing the features map.

At each identified trail a recording was begun and the rover was walked along the

trails at a pace slow enough to ensure accurate assessment of trail location and shape.

Location was more important than exact shape, especially when recording the trails as a

line feature, because the existences and extent of the trails was of highest importance.

Where possible, though, the shape of the trails was accurately represented.

Other features were also recorded. A watershed extent polygon was created to

allow for a boundary shapefile containing the trails and other significant features. Sewer

access caps, of which there were quite a few contained within the park, were recorded, as

were storm drains which were both independent points and parts of diversion channels

running parallel to contours of the steepest slopes within the park. A large wet

spot/spring was recorded as a polygon to map its extent and to help judge its

contributions to the discharge of the creek. Total station benchmarks were also recorded

Both the total station benchmarks and the pour point were recorded with an

average of 100 position readings to ensure the accuracy of the point data, there being no

room for inaccurate data for those points. Other readings were less intensive: trail

readings were taken as the carrier walked at a slow to medium pace, only stopping if the

satellites were not being picked up by the rover unit. Points that demanded less assurance

of accuracy were recorded with a minimum of five readings. Area polygons were

recorded by establishing corners and pause the recorder to allow the carrier to move to


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another position and resume recording; at each corner a series of 3 position recordings

was taken to ensure corner establishment.

After the data was collected the files were viewed in GPS Pathfinder 3.10 and

differentially corrected using data from two base stations local to the Bay Area

(Richmond and Berkeley). Editing of points was intensive at this stage of the process;

the trail area files in particular needed major massaging to take on a shape that adhered to

the actual features. Once the data was differentially corrected and edited, the files were

combined and exported as shapefiles. This allowed for the creation of maps of Glen

Canyon Park in ArcGIS.

To conduct the longitudinal profile we used the Topcon GTS-235 Total station

and following the Harrelson’s field survey procedure. We collected data along the last

portion of the streams’ reach, before it goes into an underground duct. The total station

was placed at bench mark one (BM1) which was established by the placement of a stake

and located in UTM by use of the Trimble GPS. BM2 (also located in UTM by use of

Trimble) was established at the site of a sewer cover that is sited across the gravel road

adjacent to the creek. BM2 was then used as a backsight for the instrument to ensure that

gather accurate data. The placement of BM1 was convenient because the entire extent of

the streams reach was within its sites.

Data points were collected along the length of the stream at the edges of the

defined channel. Bankful was an ambiguous feature to locate due to the lack of flowing

drainage of the stream. The breaks in slope and slope’s bottom of the eastern bank were

recorded. The western bank was a steady slope from the horizontal of the dirt trail above

it until the channel’s edge below, no features recorded there.

4. RESULTS

4.1 Initial Site Assessment Our initial site assessment proved to be an interesting experience. We first visited

towards the end of October and because there hadn’t been much rain, Islais Creek had

been reduced to a mere trickle. We ventured deep into the canyon, dodging the thick

blackberries and ivy to see if there was a more significant flow further upstream. We


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discovered that it was running at a very low flow throughout the stream. We noticed a

significant damp, soggy spot in a clearing mid-way up the Canyon and wondered if there

was either a leaking sewer system contributing to flow, or potentially a spring that could

be contributing to the small amount of flow in the creek.

We noted significant sedimentation caused by erosion of the hillside, presumably

due to human use and trail-making. A particularly affected area was the main access road

near the lower reach of the stream. Figure 8 is a field sketch of the area showing

channels that form from concentrated runoff during winter rains. Several attempts to

address the problem were evident, including placement of water bars along the west side

of the main access road, placement of straw wattles in gullies and channels, and planting

of native vegetation. It is difficult to know how effective the water bars are without

being there during a storm event. The other efforts seemed to be ineffective, since the

straw wattles were no longer along contour, were decomposing and the native plants

seemed to be struggling. Flag and signs were placed where restoration was occurring to

alert visitors to for the need to stay clear of the area.

In addition to gathering evidence of erosion and sedimentation problems, we set

out to delineate the effective watershed caused by urban development. In order to

determine if the Glen Canyon Park area was in fact the watershed of Islais Creek, we

surveyed the perimeter of the park for any areas where urban runoff was being channeled

into the park as opposed to being caught by San Francisco’s storm drain system. This

was done along the length of O’Shaughnessy Blvd., Bosworth St. and during the course

of our trail mapping. While we did not check the south eastern corner of the watershed

for a hydrologic link, we made the assumption that all urban runoff was captured by the

storm drain system for the purposes of preparing figure 7.

A major problem at the park, which is designated as a significant natural area by

San Francisco Recreation and Parks Department, is the fact that the dogs on leashes rule

seems to be disregarded by nearly every dog owner. Dogs were running into the creek

bed, which stirs up the sediments, destroys restoration efforts, and contributes fecal

matter to the stream.


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Figure 8 - Field Sketch of Lower Stream Reach

Picture Area


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4.2 Mapping of Impervious Surfaces


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Trail Map Discussion The mapping of the trails throughout the park helped to prove areas of direct and

indirect connectivity to the creek within the canyon. Trails in the northwestern portion of

the canyon are directly next to, and sometimes on top of, the creek bed as it exists in that

area. The main trails of the canyon (an decommissioned paved road on the east side and

a wide hard-pack dirt trail on the west side) have are parallel to the creek’s longitudinal

profile for about half of its length, until the chert outcroppings split the canyon at the

north end. The east side main trail keeps the east side hill trails from connecting directly

to the creek, but the impervious surfaces allow runoff to spill onto and through the trails

to the creek. This provides indirect connectivity that would allow some sediment eroded

from the trails (which on the steep slopes becomes water channels in a rain storm) to

wash across the trails and into the creek. This is especially acute on the west side where

the trails becomes small but exists at the bottom of a steep slope covered in eucalyptus

where lots of sediment washes down the creek at small trails on the steep slopes which

are becoming rills.

4.3 Mapping of Lower Stream Reach The group surveyed the last 50 meters of the Glen Canyon reach of Islais creek

before it goes underground into a sewer system culvert drain. This is well over 30

channel widths as the median width is less than one meter. This is also the area where the

most extensive restoration has been completed.

We selected this site to conduct the longitudinal profile because the creek bed is

typical of other portions of the creek in width and bed material, the sinuosity is also

typical of other portions as well. The stream type is difficult to determine due to the large

amount of organic material in the bed, and lack of morphological expressions of bankfull.

The stream type can be interpreted to be a Rosgen B6 type from the slope and sinuosity,

but bed material is not extensively clay or silt as much as it is humus. This is due to the

stream lacking enough discharge to be able to transport anything besides suspended

load. When typed against the Montgomery Buffington Method the channel morphology

nearly resembles a pool riffle type, however the uniformly fine bed material gives the

channel more of an appearance of a colluvial hollow. I general, the highly degraded and


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urbanized nature of the stream system make it difficult to classify it in any kind of system

developed for more natural streams.

The site data we collected may prove useful in future surveys as a baseline to any

changes that occur overtime from the result of the restoration itself. The floodprone and

bankfull features were not identifiable due to the lack of fluvial activity to clarify the

drainage patterns.

The longitudinal profile was produced from the channel data points (in meters)

and using Excel spreadsheet (Sinuosity=1.17). This figure was arrived at by calculating

the length of the channel itself. Each length between points was calculated with the

Pythagorean distance equation and added together and this total length was divided by

the total length of the valley (channel length/valley length & Slope=2.4%). This figure

was derived by dividing the total change in elevation by the total channel length (change

in elev/change in length). The profile graph was then produced using the added lengths as

points and the averages of elevation between the paired points that defined the edges of

the channel.

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74.5

75

75.5

76

76.5

77

77.5

78

78.5

79

0102030405060

Channel Distance (Meters)

Ele

va

tio

n A

bo

ve

MS

L (

Me

ters

)

Figure 9 - Longitudinal Profile of Lower Islais Creek Reach. Blue line is approximate thalweg location, yellow dots are bottom slope breaks, and pink dots are top slop breaks. Vertical exaggeration is 10x.


26

Figure 10 - Map view of lower stream reach survey. Blue line highlights difference between surveyed stream channel and prediction of GIS watershed model

5. SUMMARY & RECOMMENDATIONS Our investigation of the network of impervious surfaces found that in most places,

there is not a clear connection between channeled runoff and Islais Creek. In much of the


27

park where evidence of channeled runoff existed upslope, the thick riparian corridor and

gentler slopes of the valley floor prevented a direct connection by causing runoff to seep

into the stream as sheet flow. However, we did notice two areas of particular concern.

The first was on the lower reach of the stream where a degraded road that

provides access to Silver Tree Day Camp captures runoff from several sub-watersheds

and feeds directly into the stream before it is culverted. The road is an old paved road

that has not been maintained and is now mainly gravel. Figure 9 shows a field sketch that

was made illustrating the runoff paths as well as some measures that were taken to

address the problem. They include 1) planting of native vegetation in the rills to

encourage infiltration and decrease velocity, 2) construction of water bars to enourage

channeled water to enter the stream as sheet flow and 3) placement of straw wattles. We

also noticed areas where gravel had been used to fill parts of the main access road that

had been scoured out by water.

It seemed that many, if not most of the measures were failing, as noted by the

Friends of Glen Canyon and our own field observations (section 4.1). The management

plan for the park recommends rebuilding the road and outsloping it, to discourage water

to be channeled into the creek. However, the is no discussion of how the road would be

outsloped and where water would end up being channeled, if not in the stream. We

believe a more permanent solution would envolve the complete repaving of the road with

permeable pavement. This would 1) help storm runoff drain into the Islais Creek as sheet

flow, and 2) provide a more managed look that could reinforce the idea of the creek and

hillslopes as managed areas not to be walked around on.

The other place where runoff is being channeled into Islais Creek is on the west

side of the creek between the culvert and Silver Tree Day Camp. The west wall of the

canyon here is extremely steep and there are some unplanned trails that run totally

downslope as described in section 4.2. This area has potential to add significant amount

of sediment to Islais Creek. A look at the trail map shows that there is completely viable

alternative route to get to the Silver Tree Day Camp. We recommend closing the trail

with natural looking wooden fencing and a sign to ensure visitors that it is being closed to

help the stream. In addition to closing the trail, it could be tilled and replanted with


28

native vegetation. This was not recommended in the SF Park and Rec management plan,

but given the presence of a better managed alternative route, it seems completely feasible.

While the two areas just discussed are significant problems and better

management is needed, the bigger story is that the stream simply does not have enough

power to mobilize sediments. For this reason, we believe that the bigger issue, rather

than input of sediments from upslope sources, is the addition of organic matter from

riparian vegeation and sediment from stream bank erosion. In addition, heavy use by

visitors and dogs disturbs stream banks and beds. Therefore, we highly concur with the

recommendation in the urban forest management plan for the removal of weedy

understory and the creation of open air sunlight-penetration areas. This would go a long

way towards reducing sedimentation in the stream by reducing the input of organic

matter. In addition, structures could be put in place, such as logs, boulders, and the like

in order to concentrate stream flow along a narrower path and create pools and riffles.

This has been done in one small area of the stream, where the natural spring comes into

it, but it should be done all along the stream channel.

However, along with thinning of riparian vegetation would have to be installation

of barriers, restrictive signage, and the development of an overall more managed look and

feel to the park. This park is a highly utilized haven for the residents of Glen Park and

the city of San Francisco and is very much valued for its wild feel. Therefore, it would

be a very difficult task to tell people to stop hiking on the now impervious trails that

traverse the canyon. The problem of sedimentation and the detrimental effects that it can

have on streams is not common sense to most people, so more education and outreach to

teach people to control their dogs or impose stricter dog walking guidelines would be

beneficial. There is prohibitive signage concerning keeping dogs on leashes, but some

explanation of the bigger problems associated with it could help enforce it. Although

monitoring the park with a paid staff worker would be unlikely, perhaps one of the

neighborhood association groups could organize a volunteer program for someone to

walk around the park informing disobedient dog owners of the problems associated with

letting their pets run free.


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The urban forest management plan specifies that large eucalyptus be kept in

place as a habitat for large birds of prey (ex. Great Horned Owl). The management plan

could be improved by specifying the planting of native trees in a long term replacement

project of the exotics within the urban forest. There is something to be learned from

Dragonfly Creek in the Presidio regarding large tree removal. The watershed there seems

to be thriving despite the removal of countless invasive Eucalyptus. They also used

successful methods of covering the stumps with black plastic for at least a year to keep

the Eucalyptus from regenerating, which could be used as well. There are local case

studies and the results of these should be analyzed and applied further in Glen Canyon.

Further research that could benefit Islais Creek in Glen Canyon and its watershed

would be a water-quality analysis, to assess whether there is input into the stream from

the urban sewer system. We mapped many sewer caps and there is an anomalously wet

area that is most likely a spring, but there has been speculation that it could be from

leaking sewer pipes. In addition, a more comprehensive stream assessment could be

performed with the thinning of riparian vegetation. It would be beneficial to determine

what the stream looked like in its natural state. While we performed a stream survey of

the lower reach, it was difficult to interpret without previous stream mapping. Therefore

our survey can be used as information for future longitudinal profiles or cross sections.

6. REFERENCES San Francisco Parks and Recreation Department. Significant Natural Resource Areas

Management Plan. Final Draft. February 2006.

Glen Canyon Park Improvement Plan. Community Meeting No.2. Meeting Notes and

Powerpoint Presentation. School Of The Arts Theater. 10/23/03.

Glen Canyon Park Improvement Plan. Community Meeting No.3. Meeting Notes and

Powerpoint Presentation. School Of The Arts Theater. 02/18/03.

California Geologic Survey. Department of Conservation, Division of Mines and

Geology. Seismic Hazard Zone Report for the City and County of San Francisco,

CA. 2000. Seismic Hazard Zone Report 43.


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Jennings, C.W. and Burnett, J.L., 1961, Geologic Map of California: San Francisco sheet:

California Division of Mines and Geology, scale 1:250000.

Griffith, Lucas. 2006. Islais Creek reinterpreted: An exploration of restoration designs in

the urbanized context of San Francisco. Senior Thesis, University of California,

Berkeley.

Jenks and Loenardson. 2004. Daylighting Islais Creek : a feasibility study. University of

California, Berkeley University of California, Berkeley.

Department of Water Resources. San Francisco Bay Hydrologic Region: Islais Valley

Groundwater Basin. California’s Groundwater Bulletin 118. Last update: 2004.

islais creek sediment source assessmentonline.sfsu.edu/jerry/geo_642/studentprojects/2007/glen...

Documents