and report results so that this work can be repeated in...

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Assessment of a Reach of Lobos Creek

in the Presidio of San Francisco (by Tracy Andres, Jeanne Depman, Meridith Fonseca, Siwen Gao)

December 18, 2006

Abstract: The Presidio’s distinction as a national park in an urban setting is unique. The health and preservation of its natural resources

require substantial effort, considering the impact of residential and commercial development immediately to the south and east. Lobos

Creek flows approximately one mile through the southwestern portion of the Presidio. It is the last free-flowing creek in the city and is the

primary source of potable water for the Presidio. Field work, focused on a reach of Lobos Creek between 19th and 20th Avenues, was

conducted during the month of November 2006 in an effort to understand current channel dimensions and water quality. The

project team included Tracy Andres, Jeanne Depman, Meridith

Fonseca, and Siwen Gao. Results of our longitudinal profile and cross section are compared to results published in a 1995 report prepared

for the Golden Gate National Recreation Area. Water quality testing was also conducted. Results are discussed.

Introduction

The Presidio of San Francisco is located at the northern tip of San Francisco. In 1994 it became a unit of the Golden Gate National Recreation Area, as

well as a national park. Its 1491 acres encompass a landscape rich in historic culture and physical diversity. It is an aspect of the latter on which

this paper will focus. Three watersheds comprise the Presidio. Tennessee Hollow, approximately 270 acres, drains the eastern portion of the park to

the San Francisco Bay via the recently restored Crissy Field marsh on the north coast. Fort Scott, approximately 200 acres, drains a northwest portion

also to the San Francisco Bay. The third watershed, Lobos Creek Valley, is

approximately 2080 acres and drains to the Pacific Ocean. Just five percent of this watershed lies within the Presidio in the southwest region while the

remainder extends across residential development to the northern portion of Golden Gate Park (National Park Service 1996). Lobos Creek is the only

remaining naturally occurring surface water drainage in the City of San Francisco. It is a first-order stream with no tributaries and its length is

approximately one mile. Our project focuses on a reach of Lobos Creek parallel to Lake Street between 19th and 20th Avenues. A longitudinal profile

and cross section were measured. Additionally, water quality testing was conducted. Methods and results for each step are discussed. Comparisons

are made to longitudinal profiles and cross sections published in a 1995 report for the Golden Gate National Recreation Area. The primary objectives

of our project were to establish benchmarks, take accurate measurements,

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and report results so that this work can be repeated in the future, and

changes in the creek over time can be analyzed.

Background Although Native Americans have inhabited the San Francisco Bay region for

over 10,000 years, occupation of the site of the Presidio dates to 740 A.D., or just 1266 years ago. Evidence suggests the Ohlone/Costanoan tribe used

the landscape for hunting, fishing, gathering, and periodic burning to promote the growth of native grasses. During this time Lobos Creek flowed

unrestricted through dune fields from its origin near Mountain Lake to its outlet at Baker Beach (National Park Service 1996). The next wave of

occupancy occurred in 1776 when Spanish explorers established El Presidio (translated as fortress, or military post). For the next 218 years, through

military occupation by Spain, Mexico and the United States, the Presidio would evolve to become the most significant post on the West Coast.

Consequently, the landscape was manipulated from barren scrub and dune

fields to a strategically forested, developed environment. Lobos Creek was altered as well. As one of a few local freshwater sources, most of the creek’s

surface flow downstream of Lincoln Boulevard was diverted and used as a drinking water supply from the mid-1800’s onward (National Park Service

1996). In 1851 the Mountain Lake Water Company was formed to bring water from Mountain Lake in the Presidio to other regions of San Francisco.

In addition, the mouth of Lobos Creek was dammed in 1857 to provide water to the growing Gold Rush population. Two million gallons of water per

day traveled by flume, tunnel, and pump to two reservoirs on the north slope of Russian Hill (Hanson 2005). Based on an 1856 U.S. Coast and

Geodetic Survey Map, there is no clear surface connection between Lobos Creek and Mountain Lake. However, earlier sketches by Spanish explorers

show Mountain Lake draining into the creek (Bancroft, date unknown; Schanz, Julin, and Odaffer 1995). Mountain Lake contributes water to the

creek indirectly through subsurface flow. However, the primary source of

water to Lobos Creek is groundwater seepage along the south bank.

Geomorphic Evolution of Lobos Creek The area of the Presidio where Lobos Creek flows was originally dune fields,

as was much of western San Francisco. A brief summary of Lobos Creek through geologic time provides an understanding of its evolution. The Colma

formation is a rock stratum that formed from estuarine sands, silts and clays which were deposited 80,000 – 120,000 years ago during the last major

interglacial period when sea level was higher than today. The Colma formation locally forms a thin veneer over rocks stretching from the Golden

Gate headlands to Angel Island and south to the peninsula (Elder 2001). The Colma formation was surface deposit and the watershed generated more

runoff than infiltration. A stream channel was likely initiated and flowed as

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an ephemeral stream. Approximately 5000 – 6000 years ago dune sands

were deposited by strong easterly winds blowing from Ocean Beach. Consequently, the watershed surface shifted from Colma deposits to

permeable sands. Rainfall was infiltrated and the water table built up beneath the sands. Groundwater flowed towards the Colma channel and

emerged as surface flow. The hydrology of the creek then shifted from an ephemeral to a perennial spring-fed stream. The constant flow prevented the

channel from filling in with wind blown sands while dunes formed around the creek (Schanz, Julin, and Odaffer 1995).

Present Setting of Lobos Creek

Lobos Creek flows approximately one mile through the southwestern portion of the Presidio. It is the primary source of potable water for the Presidio.

From its headwaters near 17th Avenue the creek flows westward toward Lincoln Boulevard. At approximately 24th Avenue it enters a culvert, is

diverted in a northerly direction, and flows under Lincoln Boulevard. On the

north side of Lincoln Boulevard the creek surfaces and enters a water intake structure. From this structure, the majority of water is piped to a treatment

plant. The remaining water is considered bypass and continues flowing in a northwesterly direction on the surface, through the grounds of a private

residence, and in a culvert to an outfall structure at Baker Beach where it empties into the Pacific Ocean. Presently, between 1.2 million and 1.7

million gallons per day flow from Lobos Creek to meet 80% of the Presidio’s demand (The Presidio Trust 2005). The remainder is met from the Hetch

Hetchy system. The current population of the Presidio is approximately 5200; 52% of whom are residents and 48% of whom work in businesses

located in the Presidio (The Presidio Trust 2006).

In December 1995, three engineering/environmental firms released a collaborative preliminary restoration plan for Lobos Creek. To our

knowledge, this report is a precursor to a comprehensive environmental

assessment published by one of the firms in January 1996. The preliminary plan includes a series of longitudinal profiles and cross sections. Oddly, the

environmental assessment does not include such information. For our project we chose a particular reach of the creek that had been measured by

the firms previously and included in the preliminary report. Unfortunately, we were not able to obtain the full report, but rather, a few pages with

longitudinal profile and cross section illustrations. Significant information such as elevation benchmarks are not described in the pages we received.

Nonetheless, we have attempted to compare our results, to the extent possible, to those of the report.

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Longitudinal Profile A longitudinal profile was conducted on November 3, 2006. The survey team

included Siwen Gao and Jeanne Depman. Approximately 420 feet of the creek was measured in 10-foot increments. The starting point was

downslope from a house located at 10 19th Avenue*. It can be identified by its cream color and Spanish tile roof. This point was chosen because

vegetation in the creek upstream of 19th Avenue made the route unnavigable. The starting point has been monumented with a wooden stake

and pink flagging. The end point was downslope from 20th Avenue, immediately downstream of what appeared to be a small landslide on the

south side of the creek. The address of the house nearest our end point is 2 20th Avenue*. The house can be identified by its brown shingles and dark

green trim. This end point was chosen for a couple of reasons. The reach included one bend and measured at least 20 times the bankfull width of the

channel which we measured as 16 feet. The end point can be identified by

pink flagging on the upturned tree roots extending into and embedded in the creek. GPS readings were taken at the start and end points utilizing a

Garmin GPS 76 unit (serial number 80205778). The start point was 10S 545888m east and 4182357m north; the end point was 10S 545752m east

and 4182348m north. Two turning points gave the survey team experience in setting up and preparing the level for use. Surveying equipment included

a Sokkisha Automatic Level B2A, a 300’ decimal feet measuring tape, and a decimal feet stadia rod. The weather on November 3 was overcast.

Precipitation (0.24 inches) the day prior had likely influenced water surface elevation in the creek however, lack of measurement data on November 2

prevented comparison analysis.

* Google Earth identifies this address approximately 100 feet south of its actual location. Ground truthing proved this.

Method The elevation at our starting point was initially estimated by a GPS reading

of 7.71 meters (25.29 feet). Considering the GPS unit’s accuracy rating of 31.8 meters, and a 1993 measurement of 47 feet (according to the 1995

report), we were skeptical of the 7.71 meter reading. Although the National Geodetic Survey / National Oceanic and Atmospheric Administration have

established two elevation benchmarks in the southwest region of the Presidio, backsighting to either of these points would have required

significant additional time since they are more than 0.25 miles and 0.75 miles from our starting point. We successfully located the latter near the

entrance to the Presidio Golf Club on Washington Boulevard. The elevation at this benchmark is 307.22 feet according to the National Geodetic Survey

of 1991.

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We considered calculating elevation based on a combination of contour lines, slope angle and slope distance. We knew the house at 19th Avenue was 100

feet elevation based on aerial photography and contour line data downloaded from USGS San Francisco Bay Area Regional Database.

However, a fence midway down the slope from the house prevented us from accurately measuring slope distance from creek to house. Another method of

simply backsighting from the house to our starting point in the creek was not possible due to the steep angle of the slope, the thick vegetation, and

the inability to position the level on the slope.

We decided to determine elevation from contour lines. Based on our field map (see attached) the starting point of our longitudinal profile is at 50 feet

elevation. This is more in sync with the 1993 measurement of 47 feet. Using the level, the height of the instrument was determined by placing the stadia

rod at the starting point stake and adding the level reading of 4.08 feet to

the elevation of 50 feet. Foresight readings were taken at 10-foot increments. See Lobos_long_profile spreadsheet for detail.

The 1995 report mentioned above includes longitudinal profiles from 1993

and 1915. A third profile labeled Colma was derived from local well boring data, soil corings, and surface outcrops (Schanz, Julin, and Odaffer 1995).

Comparison of our results to the 1993 and Colma longitudinal profiles revealed a similar drop in stream gradient of three feet between 19th and

20th Avenues. For 1915 the drop is approximately eight feet. We were unable to determine the reason for this substantial difference. However, the

report indicates that by 1915 the U.S. Army had constructed a pump station and water treatment plant at the mouth of the creek (Schanz, Julin, and

Odaffer 1995). Perhaps this had some influence but the mouth is nearly a kilometer downstream from 19th Avenue.

Throughout the surveying process we encountered some challenges. The most significant was determining elevation, as noted above. Secondly,

vegetation in the creek and on the banks was abundant. Determining the location of the thalweg amidst the dense vegetation was occasionally

difficult. The primary plant in the creek was watercress. According to Darren Fong, Aquatic Ecologist for Golden Gate National Recreation Area, it is native

and grows in sunny areas where water is fairly slow flowing. It doesn’t endanger the creek and there is no call for its removal (Darren Fong, 13

November 2006, e-mail). Lastly, the fine sand substrate created a ‘quicksand’ type of bed surface and made walking in the creek a challenge.

Following is the longitudinal profile created from our data.

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Lobos Creek, The Presidio, San Francisco

Longitudinal Profile: 19th-20th Avenue

42

43

44

45

46

47

48

0 30 60 90 120

150

180

210

230

260

290

310

340

370

400

Distance (feet)

Elevation (feet)

Cross Section In order to compare the cross-section previously described in the 1995

Restoration Plan of Lobos Creek, we chose to measure at the same portion of the creek which was on 19th Ave. The cross-section was done by Jeanne

Depman, Siwen Gao and Tracy Andres from 11:00am to 4:00pm on Nov. 17th, 2006. It has previously rained the two days before. Based on ocular

observations, the flow seemed faster and deeper than that of Nov. 3rd, 2006, the day we finished the longitudinal profile. However, no flow measurement

was done on Nov. 3rd so we could not make any scientific comparisons of stream flow.

We decided to set up the Level at the same spot where we established for

the longitudinal profile because it was the only accessible, flat surface close enough to capture the numbers on stadia rod. Besides, this allowed us to

use the elevation of 50 ft. and the same beginning point of the longitudinal profile to determine the height of the instrument. This time, we measured

the stake at this beginning point was 2.6 ft above the stream bed and obtained UTM from the GPS (refer to “Longitudinal Profile” section). Jeanne

and Siwen held the tape twice the maximum depth which was 4.4 ft above stream bed. Siwen placed the beginning of the tape on the South Bank and

Jeanne placed the end on the North Bank. Two rebars with pink flagging were left at each point of the banks. The flood-prone width was measured to

be 23.95 ft. Then, Tracy held the stadia rod and measured the cross-section.

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She marked the thalweg at 12.55 ft on the tape. We plugged the data into

an Excel spreadsheet and obtained the following result:

Cross-section of Lobos Creek

at 19th Ave.

47

48

49

50

51

52

53

54

55

0 2 3 4 5 6 7 8 9 10 11

12.55 13 14 15 16 17 18 19 20 21 22 23

Distance on tape from South Bank (ft.)

Ele

vati

on

(ft

.)

At the end of the cross-section, our team did not make a turning point and measure the back sight which could have increase the accuracy of our data.

The slopes were steep so we could not place the level horizontally to measure the higher portions of the banks. In the 1995 report, a cross-

section was done from the top to the end of both banks at 19th Ave. However, their method descriptions were not found. In order to measure the

South Bank, Jeanne climbed up the bank with a tape and reached the fences around the house. The slope distance was 61.6ft. The angle was read 34

degrees from a Sunnto clinometer. Unfortunately, the fences blocked Jeanne from the house which elevation was 100 ft. These data were not accurate

enough to determine the elevation of the stream at 19th Ave. For the North

Bank, too many willows were blocking the view so the angle was not measured.

From the cross-section graph, the Thalweg was located approximately at the center of bank-full stage (from 6 ft to 19 ft on tape). The similar result was

shown in the cross-section in the 1995 report. The position of Thalweg remained in the relative same place. Besides, the South Bank was steeper

than the North Bank from our cross-section. There was no significant floodplain in Lobos Creek. Little changes in creek flows during storms and

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the lack of large flood events limited sediment movement and changes in

stream features (Schanz & all, 1995).

Stream Type / Classification Classification of Lobos Creek was assessed using the Rosgen system as

found in the United States Department of Agriculture Forest Service document entitled: Stream Channel Reference Sites: An Illustrated guide to

Field Technique. We used the characteristics of the same reach where we have taken all of the measurements. The creek has low to moderate

sinuosity, and a sand bed with few rocks and no gravel. The flood prone measurement is 24 ft. and bankful is 16ft., therefore the floodprone over

bankfull is 1.5 (the entrenchment ratio). This entrenchment ratio and sand bed suggests that Lobos creek is a type B5. (However, more exact

measurements of the width/depth ratio, sinuosity, and slope may indicate that the classification is actually a type F). The creek is moderately

entrenched with infrequent pools, and a gentle slope with abundant

vegetation. Water cress is abundant in the stream bed. On the south bank (maintained by homeowners) is mostly non-native decorative type plants ( a

couple palm trees for example) and exotic ivy, whereas the north bank is maintained by the Presidio and is predominately native scrubs and trees

(native coast live oak and willows). The threespine stickleback is the only native fish in the creek.

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Plan View (sketch)

Cross Section (sketch)

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Water Quality For the past several years a non-profit organization (The Urban Watershed

Project) has been monitoring water quality in the Presidio. This non-profit is directed by Doug Kern, but works closely with the Presidio Trust and the

National Parks Service. This testing monitors several locations in the Tennessee Hollow Watershed as well as Lobos Creek, and the tap water.

The San Francisco Presidio is surrounded on two of its three sides by the city of San Francisco. When one views a map of San Francisco the park

may seem like a lush island compared to the concrete grid squares of the city streets. In actuality the Presidio is not at all an island because it is

heavily affected by the surrounding urban environment. As earlier noted the watershed of Lobos Creek extends far beyond the borders of the park which

ultimately have a negative affect on the water quality. It is clear that since the watershed is home to residential

neighborhoods, tourist attractions, golf courses, dogs, etc., all activities end

up in the water, including driving and/or taking the bus. This vehicular use has a negative urban impact on the water quality. Water picks up almost

everything it comes in contact with. That includes the tiny particles of rubber that wear off every time a car is driven, or the small amounts of oil that leak

from cars, etc. These all get washed into the watershed. Some of these places in the watershed are locations where people do not always put their

waste into the waste bin, or fertilizers are sprayed regularly. Therefore it ends up in the watershed. This causes pollution in the water and negative

affects on the habitat. The affects of the urban nature of the Presidio can also be seen in the

Lobos Creek watershed, which extends beyond the parks boarders into the city. Note that watersheds do not follow boundaries that are not physical.

For example water will flow another direction because it is diverted by a physical boundary like a channel or a solid fence, but it will not flow another

direction because of a boundary like property ownership or a political

boundary. This is important because this parks does not have physical boundaries distinguishing it from the surroundings.

Uniquely in Lobos Creek there are some older pipes which drain into the creek and no one seems to know where they originate. These urban

inputs are causing problems like high nitrate levels, low dissolved oxygen, as well as high bacteria counts. These tests prove that although the park may

be separate in a sense from the city it is not an island. To investigate the water quality Meridith and Tracy participated in two water quality testing

days this semester, in order to add to previously existing data found in the water quality excel spreadsheet (digital format).

On Tuesday Nov 28th in the morning we tested at four locations. We tested at the 22nd Ave. parallel because it is accessible and downstream of a

cement structure that a sewage pipe passes through. This is one of the

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locations we regularly test at to make sure the pipe is not leaking. We also

tested at the 20th Ave parallel both in the stream and in a clay pipe coming out of the side of the bank. The clay pipe is a regular test because it is an

unknown input and usually high in nitrates. The center of the stream is tested just slightly upstream of the pipe as a control (or way to compare

data). We also tested at the 18th Ave parallel to make sure that the upstream section of the creek is being monitored. Note the downstream

reach of the creek is monitored by those who divert the water for the Baker Beach treatment facility.

All of the locations were tested for water temperature, dissolved oxygen, percent saturation, pH, conductivity, salinity, total dissolved solids

(TDS), water clarity, sheen, nitrates, and phosphates. These tests are each done three times, and the average of those three is used to minimize errors.

In addition to these regular tests Meridith made three tests in which natural cotton were placed in screens and left in the creek for one week. Two

of the tests were covered with sediments, mostly small sand particles and

gave no light under the UV light in the dark. One test which came from the 20th Ave seep A location (the seep at the fallen fence along the south bank,

upstream of 20th Ave parallel) gave a small amount of light while under the UV light.

The testing showed that downstream of the sewage pipe was the highest nitrates and coldest temperature. To view the rest of the results

please view the digital data; most results were within normal ranges. For the second day of testing conducted on December 5th (also a Tuesday morning)

we tested the several seeps located on the south bank of the creek between 20th and 22nd Ave. These seeps have been historically high in nitrates,

therefore this testing aimed to pinpoint which seeps were highest and map them with a GPS and field map. With the dense amount of vegetation both in

the creek bed and the bank the odor was either a metallic sewage smell or just decomposing organic matter.

The December 5th testing revealed that location LC022 was at 10.9

mg/L nitrates whereas one week earlier it tested at 20.9 mg/L. The phosphates and all other testings stayed generally the same. The location

which tested highest in nitrates tested at LC020 pipe (clay pipe at the 20th Ave parallel) at 39.0 mg/L. This is very high but there have been tests over

50 mg/L before.

Why monitor the water quality in this unique urban watershed? The National Parks mission statement says:

“The Service thus established shall promote and regulate the use of Federal Areas known as national parks, monuments and

reservations…by such means and measures as conform to the fundamental purpose of the said parks, monuments and reservation,

which purpose is to conserve the scenery

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and the natural and historic objects and the wildlife therein and to

provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future

generations.” (National Park Service 2006).

The Service mission as written above emphasizes preservation of these special places unharmed in their history, scenery, and wildlife for

future generations. None of the parks could fulfill the mission statement if it wasn’t for water. The real issue is that it must be clean water. Note that

water that is polluted or of poor quality is sometimes worse than no water at all. Therefore the Service must manage water quality to ensure that it fulfills

the mission and fosters a safe habitat.

Ultimately if the park does not do something about these nitrates it will harm the residents and the wildlife. Nitrates are known to the EPA to cause

blue baby syndrome and deprive oxygen in the blood affecting mostly

children and seniors. The safe levels for nitrates in a drinking water source are 10 mg/L according to the EPA. There are loopholes however, depending

on how many people the source serves, and if they have notified the residents. According to an University of Oregon study developing amphibians

such as tadpoles cannot survive in anything over 3 mg/L because that is a level found in nature.

Where do the nitrates in Lobos originate?

The input of nitrates is concentrated at 20th Ave and about half a block east of that upstream, but originally only nature knows. Meridith has have

spoken with the golf course in the Presidio, and at the Legion of Honor neither of them claims to use nitrate fertilizers. There is no livestock in the

area and no dogs have access to the creek. One possibility is a leaking sewage line.

In the spring of 2006 Meridith did an internship in which some tests in

Lobos were as high as 64 mg/L. So in an effort to investigate Meridith researched sewage pipeline maps from the city, and interviewed residents.

Questions included whether or not they owned their home, if they had access to the creek and if they had a bathroom in their basement/granny

units. Most people were homeowners, but few had access to the creek. Many people didn’t even know they lived next to a creek. In any event almost all

of them had plumbing of some sort in the basement, and most did not know when it was installed. Additional questions regarded the sizes of their yards

and if they used fertilizers. Both of these hypotheses seemed to go nowhere. The source is still being investigated, but ultimately unknown.

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Conclusion The Presidio of San Francisco is a storied, complex landscape. Its

designation as a national park since 1994 guarantees certain protection and preservation of its cultural and natural features. Lobos Creek, flowing within

park boundaries and serving as the park’s primary potable water source, is unique. The majority of its watershed lies south of the park in residential

development. Although the primary source of water to Lobos Creek is groundwater seepage, pollutant runoff from neighboring streets and homes

is a significant concern. Our field work was an introduction of sorts to a reach of Lobos Creek. Establishing baseline measurements through a

longitudinal profile and cross section will allow future teams to analyze changes in the creek over time. Additionally, the results of our water quality

testing can be compared to future studies. It is the latter that will require greater attention as the Presidio’s popularity as a setting for tourists,

residents, and businesses continues to grow.

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References Elder, William P. 2001. Geology of the Golden Gate Headlands. In Geology

and Natural History of the San Francisco Bay Area: A Field-Trip Guidebook, ed. P.W. Stoffer and L.C. Gordon, 61-86. U.S. Geological Survey Bulletin

2188.

Hanson, Warren D. 2005. San Francisco Water and Power – A History of the Municipal Water Department & Hetch Hetchy System. San Francisco, CA:

San Francisco Public Utilities Commission.

National Park Service. 1996. Environmental Assessment: Restoration Plan for Lobos Creek, Presidio of San Francisco, California. Prepared for the U.S.

Department of the Interior, National Park Service, Golden Gate National Recreation Area, by Harding Lawson Associates (HLA Project No. 26097),

Novato, California.

Schanz, Robert W., Kent Julin, and Gary Odaffer. 1995. Restoration Plan for

Lobos Creek. Prepared for The Golden Gate National Recreation Area, San Francisco, California. San Francisco, CA: Philip Williams & Associates, Ltd.

The Presidio Trust. 2005. Annual Water Quality Report. [Online],

http://www.presidio.gov/NR/rdonlyres/6786844C-02CF-4C7F-B2A9-8EC309A50EE2/0/WaterQualityReport2005.pdf (last accessed 18 November

2006).

The Presidio Trust. 2006. Frequently Asked Questions, Living and Working. [Online], http://www.presidio.gov/faqs/ (last accessed 1 December 2006).

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