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Larsen Creek Stream AssessmentLagunitas Watershed, Marin County
Brian BelluominiBill GoedeckeParis Good-SwanThad SheltonOscar Steiner
G642 Watershed RestorationFall 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
2
compared with 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
3
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
4
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)
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.
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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)
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
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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).
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Above the Lagunitas Bridge and up to the golf course Larsen Creek can be
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
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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 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
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restoration of the streams (personal communication with SPAWN founder, Todd
Steiner).
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
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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.
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
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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 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 14
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.
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
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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.
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
16
areas for salmon habitat. However, substantial bank erosion was also observed
occurring throughout the length of the reach.
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.
17
Equipment used:
Leica Sprinter 100 digital leveler Stadia rod Increment tree borer 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
18
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
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
19
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 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
20
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.
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
21
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.
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.
22
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.
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
23
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 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.
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0 10 20 30 40 50 60 7075.800
76.000
76.200
76.400
76.600
76.800
77.000
77.200
77.400
77.600
77.800
Longitudinal Profile
Depth of River Bot -tom
Water Depth
Benchmark
Elev
ation
0 2 4 6 8 10 12 14 16 18 2076
76.577
77.578
78.579
79.580
80.581
Cross-Section 1
Horizontal Distance
Elev
ation
25
0 2 4 6 8 10 12 14 16 18 2075
76
77
78
79
80
Cross-Section 2
Horizontal Distance
Elev
ation
0 1 2 3 4 5 6 7 8 9 1075
75.576
76.577
77.578
78.579
Cross-Section 3
Horizontal Distance
Elev
ation
(m)
9%
18%
38%
31%
4%
Cross Section 1 Pebble Count
2--8 Fine Gravel
8--16 Med Gravel
16--32 Coarse Gravel
32--64 Very Coarse Gravel
64--90 Small Cobble
Size (mm), Classification
26
23%
22%
21%
22%
11%
1%
Cross Section 2 Pebble Count
<2 Sand
2--8 Fine Gravel
8--16 Med Gravel
16--32 Coarse Gravel
32--64 Very Coarse Gravel
64--90 Small Cobble
Size (mm), Classification
1%
9%
29%
43%
18%
1%
Cross Section 3 Pebble Count
<2 Sand
2--8 Fine Gravel
8--16 Med Gravel
16--32 Coarse Gravel
32--64 Very Coarse Gravel
64--90 Small Cobble
Size (mm), Classification
27
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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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