Larsen Creek Stream Assessment
Lagunitas Watershed, Marin County
Brian Belluomini
Bill Goedecke
Paris Good-Swan
Thad Shelton
Oscar Steiner
G642 Watershed Restoration
Fall 2009
1
(SPAWNUSA)
Introduction
The Lagunitas Creek Watershed in Marin County is one of the most important
spawning sites for Steelhead trout and Coho salmon in California. Larsen Creek is a
tributary in the watershed that has some of the ideal structures necessary for fish spawning,
such as pool - riffle channel characteristics. One study was completed on Larsen Creek to
assess the habitat conditions for fish but no data existed about the spatial layout of the
creek. The purpose of our study was to complete a structural survey of Larsen Creek to
determine future restoration options and fish habitat analysis. These can be compared with
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future measurements to determine the success or failure of restoration and erosion control
practices at maintaining a pool-riffle channel. A recent study (2005) showed that the Larsen
Creek was one of the most successful streams in the watershed at providing habitat for
salmon and trout as they left for the ocean. Our study shows that with some strong erosion
control methods, Larsen Creek can continue to be an ideal habitat for Coho salmon and
steelhead trout.
Larsen Creek Watershed
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Stream Description
Larsen Creek is located in the Lagunitas Creek watershed in West Marin County,
California. It is a first order stream that flows into San Geronimo Creek. About half of the
land surrounding the Lagunitas Creek watershed is privately owned. The other half is
dived between the Marin Municipal Water District and the National Park Service (NOAA
2008). The housing density in this watershed is relatively sparse with only 6,000 residents
and 2,600 houses on about 70,000 acres.
Ownership map of land in Lagunitas Watershed (SPAWNUSA)
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Larsen Creek was chosen for its ease of access and its function as historic salmon
habitat. According to SPAWN, the tributaries of San Geronimo and Lagunitas Creeks have
higher rates of salmon spawning and juvenile habitat areas than the main creek itself. This
was a deciding factor in choosing this site.
Chart comparing rates of redds per stream area in the Lagunitas
Watershed. Spawning density is higher in the smaller tributaries.
(SPAWNUSA)
San Geronimo Golf Course (LagunitasMontessori.org)
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The San Geronimo Golf Course, located to the North and East of our study area, is
one of the biggest stakeholders of Larsen Creek. Much of the upstream reach flows directly
through sections of the golf course. Adjoining the downstream areas of Larsen Creek is a
school and community center to the West and a County-managed open space preserve to
the East that is frequently used by hikers, bikers, and equestrians. The size of the watershed
that drains into Larsen Creek is approximately 465 acres. The confluence of Larsen and
Geronimo Creek is approximately 76.2 meters and the elevation in the headwaters area is
approximately 213.36 meters (Reese et al. 2005).
Impervious surfaces are primarily in the lower reach area. Sir Francis Drake Road is
a major thoroughfare that runs roughly parallel to San Geronimo Creek near the Larsen and
San Geronimo Creek confluence. The Lagunitas School is located on either side of the
lower reach and is composed of two campuses connected by a paved road that crosses
Larsen Creek approximately 292 meters from the confluence (measurement by Reese et al.
2005). Total acreage for the amount of impervious surface for both campuses and the
Lagunitas School Road is approximately 7.2 acres with 2.3 acres draining directly into the
creek through a culvert on the east side of the creek.
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Using Rosgen Stream Classification, the first 200 or so meter stretch of Larsen Creek
from the confluence with San Geronimo Creek is a B6 channel type. The next 500 or so
meter reach is a F3 channel type. No classification was done above this point. (Reese et al.
2005). A F3 channel has a riffle/pool morphology with infrequently spaced pools, a high
width to depth ratio and is entrenched, meanders and is mostly dominated by cobbles
(Rosgen 1994). Above the Lagunitas Bridge and up to the golf course Larsen Creek can be
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characterized as more highly incised with a slightly greater stream gradient than below the
bridge. Less sediment was observed in the creek bed in the upper channel than was
observed in the lower channel. A B6 channel also has a riffle/pool morphology and a high
width to depth ratio but with less entrenchment (Rosgen 1994). It is noted for having
infrequently spaced pools, although the stretch we surveyed was more pool dominated due
to the presence of two culverts that act as drainage for adjacent areas. More sediment
deposition was observed in this lower reach. The substrate is often sand and silt or clay.
Larsen Creek looked to adjust into a class B channel with progressively lower banks as the
creek meanders into the valley bottom.
Stakeholders and Watershed History
The main stakeholders for Larsen Creek are the San Geronimo Golf Course,
Lagunitas School, residents that live along San Geronimo Creek, and SPAWN (Salmon
Protection and Watershed Network). The golf course owns much of the land that the Larsen
Creek runs through as well as some of the tributaries that flow into it (Reese et al. 2005).
The course manager seems to be impartial to the condition of the creek so long as it looks
good for golfers and restoration attempts do not affect the layout of the golf course. The
Lagunitas School greatly wants to preserve the delicate stream habitat so that the children
of the school can enjoy its beauty and observed the endangered salmon that spawn in its
waters. Some of the residents living along San Geronimo Creek and SPAWN have
somewhat differing views (personal communication with SPAWN founder, Todd Steiner).
SPAWN recently sued the county of Marin for not acting on their promise to
improve stream quality and building regulations, which forced the county into a two-year
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moratorium on building within 100 feet of any stream (SPAWN 2009). A local community
meeting was held with the county supervisor, SPAWN and concerned community
members. Members of the community were concerned that the value of their homes might
be affected, that they would not be allowed to have gardens and other modifications along
the creek corridor, and that local construction business might be hampered. SPAWN
argued that preserving the creek and endangered species that live in it will increase the
value of property located on the creek and will improve the water and habitat quality by
preventing development, making the stream a safer place for children to explore. Not
surprisingly, residents support stream restoration so long as it doesn’t affect them directly.
Many residents are very hostile towards SPAWN and its volunteers because they think that
SPAWN will report their creek-side activities, resulting in a fine by the County or forced
removal of their private structures. This makes access to the San Geronimo creek more
difficult than it may have been before the moratorium. SPAWN has attempted to modify
the way people interact with the stream in order to try and rehabilitate the riparian habitat,
water quality, and abundance of spawning fish. If the stream quality degrades to the point
where no fish return, SPAWN will have a harder time finding funding and inspiring the
community to help in the preservation and restoration of the streams (personal
communication with SPAWN founder, Todd Steiner).
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Previous Studies
A previous study of Larsen Creek was completed in September of 2005. It was done
by the Watershed Stewards Project/AmeriCorps Members under the influence of the
California Department of Fish and Game. The goal was to determine what habitat was
available for anadromous salmonids (Reese et al. 2005). They also made recommendations
for habitat improvement. At the time of the study there were two culverts pouring into
Larsen Creek causing substantial bank scouring. This is still an issue today as the pools
formed by the culverts are quite deep and channelized flow is causing substantial bank
erosion.
The 2005 study completed a habitat inventory that was found in the California
Salmonid Stream Habitat Restoration Manual and the components researched were flow,
channel type, temperature, habitat type, embeddedness, shelter rating, substrate
composition, canopy, bank composition and vegetation, large woody debris count, and
average bankfull width. However, missing from this study was a detailed physical profile
of the stream. This project therefore focused on creating a detailed spatial profile and
sediment analysis of Larsen Creek by creating a sound longitudinal profile, three cross
section studies, and a detailed pebble count of the downstream reach of the creek. This
analysis will be helpful in future comparisons to determine if restoration methods are
actually succeeding in reducing erosion and creating suitable salmon and trout habitat. The
study from 2005 found that B6 and F3 channels are especially strong places for salmon
habitat.
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Salmon returning to San Geronimo Creek in 2008 (SPAWNUSA)
Cover created by boulders and logs are safe places for fish to hide from predators
and the structure of the channel is good for restoration methods and streambed
enhancement (Reese et al. 2005). The embeddedness of Larsen Creek and the extensive
woody debris around the stream also create well-suited areas for spawning. Wood
structures protect salmon from predators, provide places for resting and reduce
competition for food and shelter. Many recommendations were made in the 2005 study
including completing an inventory of stream bank erosion, identifying sediment sources,
increasing woody cover on the pools and designing pool enhancement structures.
Salmon
The Lagunitas Creek Watershed sustains the most significant population of
endangered Central Coast Coho salmon in California (Pincetich 1999). This watershed
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supports 35 miles of Coho-bearing streams. Coho salmon have a three year life cycle. Their
first year is spent living in rivers and streams before migrating to the ocean for a year and a
half. They need substantial food, protection, and cool, well-oxidized water in order to
survive the first year of life (Flosi et al. 1999). The streams of California generally have
enough gravel for spawning but there are not enough streams with pools for the juvenile
Coho. The juveniles prefer slow moving water with a temperature between 48 to 60° F.
Coho in the early stages of their lives need access to shallow, calm water and the California
Salmonid Stream Habitat Restoration Manual recommends that restoration projects should
focus on providing shade, woody debris, and organic nutrients to ensure suitable habitat
(Flosi et al. 1999). Larsen Creek has a well developed pool and riffle system and is also a
cold-water stream away from many of the negative effects of urbanization, making it a
good site for salmon spawning. There is also extensive canopy cover that keeps the stream
cold in the summer months.
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The Central California Coast ESU Steelhead is also a threatened fish species that
lives in the Lagunitas Creek Watershed. Steelhead trout enjoy more streams and areas of
suitable habitat than the Coho salmon, and the steelhead are much generally more flexible
with their living conditions (Pincetich 1999). Over a lifetime, they can make several
spawning trips between the ocean and freshwater and actually spawn later in the winter or
in early spring. Steelheads often spend more than a year in freshwater before migrating to
the ocean, allowing them to grow larger and thus having a greater likelihood of survival.
The preferred habitat of the steelhead is very similar to the Coho. Small gravel is necessary
for spawning and logs and boulders will greatly improve habitat conditions (Flosi et al.
1999). Juveniles also prefer to live in shallow pools or riffles where the water is cool.
A study done in the spring of 2009 researched the amount of salmon in the
Lagunitas Creek Watershed that were returning to the ocean (Pincetich, 2009). 48 Coho
smolts were observed in Larsen Creek this year, almost double the amount observed in
previous years. A total of 664 smolts were observed in the entire Lagunitas watershed. This
is a very promising number because very few smolts were found in the past several years
due to drought and barriers to out-migration. Bank restoration and erosion reduction
methods will increase the likelihood that Larsen Creek can remain a strong site for salmon
populations.
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Erosion Potential (SPAWNUSA)
The presence of salmon in a stream is an indicator of overall stream health. Besides
providing a profile of the physical structure of the stream, the goal of our study was to
determine if Larsen Creek is providing ideal habitat for salmon. Previous restoration
projects and the amount of erosion and sediment needed to be analyzed in order to
determine the feasibility of a salmon habitat in Larsen Creek. The sides of the banks in
several areas looked like they had undergone bank stabilization projects in order to reduce
the amount of erosion taking place. The 2005 study recommended bank stabilization
projects as the best way to reduce erosion but unfortunately these projects had failed and
the bank continued to erode past the roots of the trees. It is important to determine the
amount of erosion and sediment in the stream because this could affect the stream
composition and reduce the likelihood of salmon using Larsen Creek to spawn in the area
of our survey.
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Evidence of streambank erosion
Survey
In September and October of 2009, our group completed three cross-sections, three
pebble counts, and a longitudinal survey of a downstream reach of the creek. On the first
visual assessment of the streambed, the stream was relatively dry with no flow in the
ripples but some standing water in the scour pools. The second visit to the streambed was
after the first significant rain of the season and there was flow through the thalweg and
significant water depth in the pools. On the third visit, the stream still had water flowing
throughout the length of the reach despite there having been no rain in between visits.
Significant woody debris and canopy cover were observed, indicating good areas for
salmon habitat. However, substantial bank erosion was also observed occurring
throughout the length of the reach.
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Access
Our study area is located on the property of a public school, adjacent to public access
off of Sir Francis Drake Boulevard, and within the boundaries of the Marrietta Larson
Preserve. There were no stakeholder protests in surveying the site, and there was easy
access from the public parking area next to the public school and San Geronimo
Community Center. Upstream of the study area, Larsen creek runs through a section of the
San Geronimo golf course. Contact was made with managers of the golf course and
permission was granted to access the section of the creek that runs through the course for
up-stream reconnaissance. Larsen Creek has no access obstacles (other than widespread
poison oak) and this is unlikely to change in the near future.
Methods and Materials
Our assessment of the lower stretch of Larsen Creek relied mainly on creating an
approximation of the physical structure of the stream by surveying a longitudinal profile
and three creek cross sections. Other features of the creek that have an impact on
streamflow, erosion and sediment yield, such as culverts and previous restoration sites,
were documented and given impact analysis.
Equipment used:

Leica Sprinter 100 digital leveler

Stadia rod

Increment tree borer
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
Trimble GPS receiver

Suunto tandem combination compass/clinometers

50 m measuring tape

Field Notebooks
Excepting the camera, all data collection equipment was borrowed from the SFSU
Geography Department with permission from Dr. Jerry Davis.
The Leica Sprinter and Stadia rod in action
Fieldwork Dates (2009):

September 26th - site selection, reconnaissance

October 17th - First day of assessment and field work, longitudinal profile

October 30th - Pebble count, cross section measurements, flow

October 31st - Pebble count, cross section measurements, flow
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Field data collection was done primarily using a Leica Sprinter digital leveler. To
create our survey, a permanent benchmark was created at the SE corner of the bridge
spanning Larsen creek at the upstream boundary of our survey area. This was our primary
control point as it is permanent and visible from the majority of our study area.
Established benchmarks
To begin our analysis of the creeks morphology, we needed to establish a permanent
benchmark, at a fixed location, by which to measure or elevations from. A small bridge
crossed the creek at the most upstream extent of our survey. The footing of the abutment
(BM1) provided a stable foundation to fix our vertical control. We set up the Leica Sprinter
on a point bar at the first meander of the creek. This location was recorded by backsighting
to BM1 and fixing our instrument height at .099 m. above the footing and 10.71 m distance
@ 36.5 degrees azimuth. During the longitudinal profile, the instrument had to be moved
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twice in order to maintain stadia rod visibility. During each move, the foresights and
backsights were recorded and monitored with secondary support from clinometers to
reinforce the azimuth. (see Longitudinal Profile Spreadsheet (LPS) for data)
To survey the longitudinal profile, a tape measure was laid in the creek along the
thalweg and station distances were calculated at every 0.5 m. The average width of the
channel is estimated to be 3 meters; thus the longitudinal profile, being 20x channel width,
spanned 60 meters of the creek. Because of areas of fallen trees and dense vegetation, it was
necessary to create turning points within the survey. Included in the profile were
recordings of water depth and substrate materials as well as major creek features such as
pools/riffles, fallen vegetation, bank erosion and culverts.
Cross sections were surveyed at several locations along the stream. Significant trees
with a small nail driven into the trunk were established as controls. These also served as
new benchmarks, as each was referenced to BM1 and recorded as BM2, BM3 and BM 4,
respectively. Height, distance and azimuth were recorded for these locations. (see LPS) The
measuring tape was stretched across the stream perpendicular to stream flow. A second
measuring tape was maintained along the thalweg to cross-reference the longitudinal
profile with the x-section and the station id. The cross section profile along with
measurements of streambed and streambank characteristics and water conditions were
observed and recorded. Cross section locations were chosen to give a representative idea of
the valley shape and to ensure easy replication of the survey in the future.
A pebble count was also performed at each of the three cross-section areas to
determine the size and quality of streambed material. This was useful in assessing
substrate in relation to water quality and possible salmon spawning areas.
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Cross Section Surveys: Vegetation is often in the instrument’s line of sight.
Erosion rates estimations were attempted using a dendro-geomorphological method
of dating exposed tree roots at eroded sections of the stream. This is done using the major
root axis as the relative position of the former, original soil and relating that measurement
to the age of the exposed roots to determine the amount of soil erosion over time (Gartner
2007). Using Gartner (2007) guidelines, the only possible roots for analysis belonged to a
small bay-laurel tree. However, due to very high moisture content within the exposed
roots, samples were very difficult to read and often fell apart shortly after coring. However,
this is a promising method of erosion rate analysis and is worth attempting for other
surveys in areas where sediment yield is crucial to stream health.
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Culverts: These culverts drain large areas of the watershed add significant amounts of sediment to the
stream. They also create artificial pools and augment the size and depth of existing pools. The effects
of the culverts could be mitigated by placing well-structured barriers to drain entrances to keep out
sediment, leaf litter and other debris.
Sediment yield: two photos of the same pool. The left photo was taken September 17 before rains
came to the area. The right photo was taken October 30 after several storms. The increased
turbidity of the water indicates a high level of sediment erosion from upstream and upslope sources.
Increased turbidity and sediment in the stream decreases salmon habitat value.
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Results
After conducting a detailed longitudinal profile, cross-section and pebble count analysis
of what we deemed the most suitable as well as heavily impacted stretch of Larson
Creek for trout and salmon spawning, we have determined several restoration
strategies that could be implemented to help preserve and enhance the stream quality
for Salmonids. The easiest and least costly way to decrease the sediment loading into
the scour pools created by the two culverts in our study area would be to surround
culvert entrances with sediment blocking barriers, such as coconut fiber waddles.
Another option is to remove the culvert draining from the Lagunitas campus and
redirecting stream flow directly into San Geronimo Creek. This would decrease
artificial pooling and sediment yield into Larsen Creek, which is likely to have a higher
salmon spawning density.
Streamflow rates could be reduced by strategically placing large boulders, logs
or root wads at the mouth of the culverts entering Larsen creek. This would
significantly slow the water flow and lead to decreased erosion downstream
As for stream bank erosion, the planting of willow stakes and other riparian
vegetation structures will act as a stabilizing agent in the cut banks as well as provide
shade and predator protection for juvenile and spawning Coho and Steelhead. Further
investigation of upstream sediment sources from hillside erosion could be remedied
through native plantings and netting on the springs and gullies that feed Larsen Creek.
Larsen Creek’s location right in the middle of an elementary school makes it a great
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place for getting Marin’s youth educated and involved in the restoration and
preservation of these crucial breeding grounds for our native and endangered fish
species. With a little restoration and community involvement the quality of Larsen
Creek should be able to rebound and sustain its fruitful characteristics for years to
come.
Longitudinal Profile
77.800
77.600
77.400
Depth of
River
Bottom
Elevation
77.200
77.000
Water
Depth
76.800
76.600
76.400
76.200
0
10
20
30
40
50
60
70
Benchmark
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Cross-Section 1
80.5
80
Elevation
79.5
79
78.5
78
77.5
77
0
5
10
15
20
15
20
Horizontal Distance
Cross-Section 2
80
Elevation
79.5
79
78.5
78
77.5
77
76.5
0
5
10
Horizontal Distance
Cross-Section 3
79
Elevation (m)
78.5
78
77.5
77
76.5
76
0
2
4
6
8
10
Horizontal Distance
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Cross Section 1 Pebble Count
Size (mm), Classification
4% 0%
2--8 Fine Gravel
9%
8--16 Med Gravel
18%
31%
16--32 Coarse Gravel
32--64 Very Coarse
Gravel
64--90 Small Cobble
38%
Cross Section 2 Pebble Count
Size (mm), Classification
1%
11%
<2 Sand
2--8 Fine Gravel
23%
8--16 Med Gravel
22%
16--32 Coarse Gravel
22%
32--64 Very Coarse
Gravel
64--90 Small Cobble
21%
Cross Section 3 Pebble Count
1%
18%
Size (mm), Classification
1%
<2 Sand
8%
2--8 Fine Gravel
29%
8--16 Med Gravel
16--32 Coarse Gravel
43%
32--64 Very Coarse
Gravel
64--90 Small Cobble
25
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References
Flosi, G., Downie. S., Hopelain, J., Bird, M., Coey, R., Collins, B. 1999. California Salmonid
Stream Habitat Restoration Manual. CA Dept. of Fish and Game. 3rd Edition. 495 pages.
Sacramento, CA.
Gartner, H. 2006. Tree Roots – Methodological review and new development in dating and
quantifying erosive processes. Geomorphology (86) 2007: 243-251
Montgomery, D., and J. Buffington. 1993. Channel Classification, Prediction of Channel
Response, and Assessment of Channel Condition. Washington State Timber, Fish & Wildlife
Report TFW-SI-110-93-002. 110 pp.
National Oceanic and Atmospheric Administration. 2008. Watershed Characterization:
Lagunitas Creek Watershed. National Marine Fisheries Service.
Pincetich, C., T. Steiner, and P. Bouley. Coho and Steelhead Smolt Outmigration from the
San Geronimo Valley, Marin County, 2009. Salmon Protection and Watershed Network.
Reese, H. and S. Philipps. 2005. Stream Inventory Report: Larsen Creek. Coastal Watershed
Program.
Rosgen, D.L., 1994. A Classification of Natural Rivers. Catena, Vol 22: 169-199, Elsevier
Science, B. V. Amsterdam.
SPAWN. 2004. County of Marin in Violation of CEQA: Ruling by Court of Appeals
Requires CEQA Review for New House in Sensitive Creekside Habitat. Accessed from
www.spawnusa.org
Steiner, Todd. SPAWN founder and father of Oscar. Personal communication over survey
period.
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