ROCK AND RICHARDSON CREEK WATERSHED ASSESSMENT
Rock and Richardson Creek watersheds comprise a small, but
important part of the Clackamas basin. The total land area of both watersheds
is just less than 9,000 acres, compared to the over 500,000 acres of the basin.
The total current distribution of anadromous fish of two to three miles within
Rock and Richardson Creeks is a mere fraction of the total habitat available in
other basin streams.
The importance of these two small streams lies in their unique
position at the edge of the Portland urban area and the fact that this area
will be substantially urbanized over the next two to twenty years. In a very
real sense, it represents an opportunity to demonstrate a new commitment,
ability and will to modify human cultural practices to maintain a sustainable
landscape through the intersection of healthy ecosystems, healthy communities
and vibrant economies.
The Clackamas River Basin Council initiated this watershed
assessment to catalyze community involvement in watershed restoration and to
offer and alternative to conventional urban development. Conventional urban
development destroys or at best severely damages aquatic ecosystems. As land is
covered with roads and buildings, rainfall runs quickly off the surface into
pipes, then to streams. It flows fast and furious, carrying all manners of
dirt, grime, oil, and chemicals directly into streams. Winter and spring flows
are higher than they ever were before, resulting in bank erosion, downcutting,
and the loss of connection between the stream and floodplain. Riparian areas
become weed and trash choked wastelands. Pools silt in, spawning gravels are
washed away, and summer flows may dry up altogether. Many urban creeks
including neighboring Johnson Creek, were quite good salmon habitat in the
1950's, now they are testimonyÝ to the
severity and problems posed by conventionally urbanized watersheds.
Oregonians have recognized the impacts of our activities on
salmonids, aquatic ecosystems and, more broadly, the watersheds and ecosystems
that sustain us. The Oregon Watershed Enhancement Board has led the way in
developing a process for assessing watershed conditions, and devising means to
repair and protect watersheds. Clackamas County has developed a stream protection
ordinance and surface water regulations. The Oregon Legislature passed Senate
Bill 1010 to improve agricultural practices near streams. Metro has adopted
Title 3 stream protection rules, which were incorporated into the May 1, 2000
Clackamas County Service District #1 Surface Water Management Rules and
Regulations. The State Forestry Board is developing new stream buffer
protections for forest practices. The State's ìThree Basin Ruleî limits point
discharges into the Clackamas Basin. Citizens have become more aware of the
magnitude of the challenge. But now that we know better, can we do better? What
will it take to do so?
The intent of this assessment is to provide a framework for
action based on a review of the many recent studies that have been completed in
this area. The Clackamas Basin Atlas, funded by the Environmental Protection
Agency and coordinated by Metro, provides a basin-wide perspective on the
entire area. Metro followed up this effort with a landscape study focused on
Rock and Richardson Creeks. Pacific Rivers Council and the Oregon Department of
Fish and Wildlife (ODFW) have done fish surveys and analyzed the health of
aquatic life. During the development of this assessment Clackamas County was in
the midst of completing a stormwater management plan for the proposed urban
areas. This assessment summarizes the findings of these and several other
studies, and provides a context for moving forward with creek protection and
restoration.
This assessment is based on the watershed assessment framework in
the Oregon Watershed Assessment Manual. As a brief summary of existing studies
it represents a snapshot of our current knowledge of Rock and Richardson
watersheds. New studies continue to generate new information about these
watersheds even as this assessment is completed. While this document is static,
the assessment process itself should be viewed as dynamic. As new information
develops, knowledge and understanding of the status and conditions of these
watersheds will continue to evolve.
Rock and Richardson Creek watersheds are part of the ecosystem
known as the East Buttes and Boring Lava Domes of southeast Multnomah and North
Clackamas Counties. These hills, rising 500 to 1000 feet above the valley floors,
were created by lava flows some two million years ago. They are part of the
same eruption cycle that built Mt. Hood. The low, mostly forested hills meet
level to gently sloping valley floors, including Pleasant and Sunshine valleys.
The streams cut down into narrow canyons as they reach the more erodable soils
south of Sunnyside Road and Highway 212.
These two watersheds have several differences as well as
similarities. Rock Creek watershed is more than twice as large in area as
Richardson Creek watershed. Richardson Creek itself has a consistently steep
gradient and flows in large part through a forested zone. Rock Creek is more of
a meandering stream, particularly where it winds across Pleasant Valley, but
falls more steeply in the lower reaches through a forested canyon. Both
watersheds are dominated by rural residential land uses with a housing density
no greater than one house per acre, but some high density housing -- with three
or more houses per acre -- is present in the southwestern portion of the Rock
Creek watershed. As illustrated by the table below, both watersheds have very
similar land cover characteristics. Agriculture dominates over one third of the
landscape, and more than two fifths of both watersheds are covered by forest
canopy.
Land Cover Characteristics by
Watershed *
|
|
Rock
|
Richardson
|
|
Land cover
|
acres
|
percent
|
acres
|
percent
|
|
Urban / built up
|
679
|
11
|
321
|
12
|
|
Agriculture
|
2,245
|
36
|
907
|
34
|
|
Forest
|
2,633
|
42
|
1,123
|
42
|
|
Shrub
|
352
|
6
|
135
|
5
|
|
Grassland, golf courses, parks, meadows
|
352
|
6
|
218
|
8
|
|
|
|
|
|
|
|
Total
|
6,262
|
100
|
2,704
|
100
|
*Source: Metro (1998).
The US Environmental Protection Agency has identified ìecoregionsî
based on similarities of topography, soils, climate, and vegetation. The area
north of Highway 212 is identified as Valley Foothills, while the area south is
called ìPrairie Terraces.î Both of these were historically forested, primarily
with Douglas-fir. Hemlock and red cedar grow in cooler, wetter areas. Oregon
white oak was found on the more well-drained terraces.
Both basins have soils and gravels deposited by past flood
events, including the Bretz floods that reached up to 400 feet in the Willamette
Valley. The basaltic lava flows lie under these soils to a depth of up to 100
feet in the valleys, deeper in the hills. Under these is the Troutdale
formation, the most important aquifer for east Multnomah and North Clackamas
Counties.
Soils tend to be poorly drained, brown silty loams and clays.
They stay wet much of the year, then dry out completely by late summer. These
soils have frustrated farmers for many years, but they are reasonably fertile
if the drainage issue is resolved.
Rural roads and highways follow the valley floors and wind
between the hills. The land is a patchwork of forest, pasture, nurseries, berry
fields, and Christmas tree farms intermingled with suburban homes on one half
to two acre lots. Views range from intimate, pastoral valley scenes to stunning
vistas of Mt Hood and the Cascade Range to the east.
The Clackamas and Mollala Indians inhabited these watersheds, as
well as land all through the Basin, for thousands of years. They fished at
Willamette Falls and other sites. They traveled through the Lava Dome forests,
hunting deer and collecting berries, hazelnuts, acorns, and camas. They likely
set fire to the woods to burn off the undergrowth, thus increasing deer forage
and making travel easier.
Euro-American settlers arrived in large numbers in the
mid-nineteenth century. They found a landscape mostly empty of humans, since
European diseases had already decimated the Clackamas and other valley bands.
They quickly set about clearing the forest away in order to establish farms and
villages. They did not have the opportunity to pause, evaluate the ecosystem
they were claiming, and learn from the previous inhabitants. Had they done so,
they might have understood the importance of protecting the creeks and
wetlands, and they might have learned that the forest helps regulate the flow
of water. They might also have learned about the ìFirst Salmonî ritual, held
each year by the Indians to celebrate the return of their most important food,
and a show of respect for these mysterious creatures.
Area creeks begin as steep first order seasonal streams that flow
off of the lava domes. Typically steep slopes lead to shallow swales that
become gravel-bottomed creeks within a few hundred yards. Other creeks join
these as they tumble through the hills. They emerge onto broad, fairly level to
rolling valley floors, where there is room to meander and join with wetlands.
This tends to be the most impacted part of the stream system, where farms and
nurseries have drained, channeled, and cut riparian vegetation to increase
space for crops or forage. Once the creeks find their way to the prairie
terraces, they cut down into the land and in effect find refuge from
surrounding land uses. The riparian zone is once again forested, spawning
gravels secure, and fish migrate up from the Clackamas and back again in their
seasonal cycle.
Overall, landscape change has compromised the aquatic ecosystem,
but not fatally so. There is time to set these watersheds on a course towards
improvement.
Rock and Richardson Creek watersheds are located in a transition
zone between the conifer forests of the Cascade Mountains and the oak/prairie
grasslands of the Willamette Valley. Research into Government Land Office Surveys
(GLO) by the Natural Resource Heritage program of the Nature Conservancy
indicates that prior to Euro-American settlement Douglas-fir forest and
woodland dominated most of the area of both watersheds. The uplands of the lava
domes were characterized by closed canopy old growth Douglas-fir, grand fir,
and bigleaf maple. Hazelnut, Pacific dogwood, vine maple, and Pacific yew
composed the understory. The valley floors were similar, but also included
western hemlock and western red cedar.
Flood plains along or near the Clackamas River had closed
hardwood forests, including Oregon ash, cottonwood, alder, maple, and white
oak. There were small patches of conifer, including Douglas-fir and western red
cedar.
Upper Richardson Creek appears to have had quite a lot of open
canopy Douglas-fir forest. This may have been an area more intensively managed
with fire by native Americans. It would have included oak trees, and possibly
ponderosa pine.
Patches of heavily burned forest were scattered throughout the
area. These could have been created by Indians to facilitate hunting and food
gathering, or may have resulted from white settlers clearing land for farms.
The downcut canyons of lower Rock and Richardson Creeks would have had similar
composition and structure to what we find there today, a mixed conifer and
deciduous riparian woodland. A few old growth conifers still exist in lower
Richardson Creek.
The Clackamas Band, related to the larger Chinookan language
group of the lower Columbia River, were likely the primary residents of the
Rock and Richardson Creek areas. They left little direct evidence of their
presence, but their primary use of the area would have been fishing in the
lower areas of both creeks. The current site of the BI-MART in Damascus was
formerly a seasonal gathering area for native peoples. By burning the uplands
periodically, they would have facilitated hunting and travel, as well as
gathering of acorns, hazelnuts, and wild berries. Generally, the Chinookans had
semi-permanent or seasonal village sites at key fishing areas (such as
Willamette Falls.) Their use of upland areas overlapped with other bands.
Uplands had ìuse rightsî agreed upon between bands, but were not considered to
be owned by anyone in particular.
The area was crisscrossed with important Indian travel routes
that were later incorporated into Euro-American settlement patterns. Among
these were the Foster-Barlow trail that connected Mt Hood, Oregon City,
Milwaukie and Portland. Generally these routes follow the valley floors and gaps
between the lava domes.
During the late 1800s and early 1900s, Euro-Americans gradually
converted the forested landscape to a patchwork of farms, including cropland,
pasture, and orchards. The soils of Rock and Richardson Creek watersheds were
not ideal for farming, so they were not the first to be cleared and tilled.
Interviews with long time residents of upper Pleasant Valley indicate that
their grandparents practiced a combination of logging and subsistence
agriculture rather than large-scale commercial farming. Dairy farming was
fairly important in this area in the 1920s and 1930s. The early farmers of the
area had to deal with these over-saturated soils by devising extensive tile
drainage systems. A current resident of Pleasant Valley unearthed a hollow
cedar drainage pipe that dates back to the early 1900's (Olson, et. al., 2000).
Farmers channelized creeks, drained wetlands, and built communities. At the
turn of the twentieth century a local pottery industry based in upper Richardson
Creek used local clay as source material and may have been responsible for some
channel modifications.
Farming peaked just before World War II, and then gradually
declined as the area became drawn into the post-war suburban housing boom. Large
farms were subdivided again and again. Areas with relatively well-drained soils
suitable for septic fields were developed as large lot (one half to two acres)
home sites that are fairly common in the land use pattern today.
Many former farms have reverted to early successional hardwood
forests over the past 40-50 years. Other farms have shifted from food
production to nurseries or Christmas trees. Statewide land use planning
initiated in the 1970s brought a halt to new subdivisions in areas outside of
established urban growth boundaries. Urban development has encroached on the
west edge of lower Rock Creek. About 50 percent of both watersheds will likely
be urbanized over the next two to twenty years. Damascus will become a densely
developed ìtown centerî according to present plans. Recent news articles point
to a further expansion of the urban growth boundary to a point several miles
east of Damascus in order to incorporate land suitable for industrial
development.
The accompanying map on page 9 showing the current urban growth
boundary and the urban reserve zone indicates the extent of this planned
urbanization.
The Euro-American history of the Clackamas River fishery dates
from the late 1800s. At that time a commercial fishery was located at the
confluence of the Willamette and the Clackamas Rivers. Harvests were recorded
to be as high as 12,000 chinook salmon in 1894. In fact, prior to 1899 the
Clackamas River was considered to be the premier spring chinook fishery in the
entire Pacific Northwest (ODFW 1992). Hatcheries were developed in the
Clackamas basin in the late 1800s, used primarily to augment spring chinook
populations, which were already in decline. Large numbers of salmon and
steelhead were introduced into the lower Clackamas in the 1950s and 1960s as
attempted mitigation for passage problems at the PGE hydro complex near
Estacada (Beyer, 1992). There are no published accounts of historic fish
populations specific to Rock and Richardson Creeks.
v 10,000-13,000
years ago: ìClovisî peoples arrive in the Rock and Richardson Creek area.
Closed forest develops in the Cascade region.
v 300-10,000
years ago: Indian culture gradually develops new technologies and land use
patterns. Deliberate burning of prairies and forests likely begins 4,000 years
ago. Clackamas Band population at 2,500.
v 150-300
years ago: Age of European exploration and discovery reaches Northwest Coast.
Trade between Europeans and Indians. Diseases begin to reduce Indian
populations. Large fires sweep down Clackamas Basin, resulting in forest stand
replacement over wide areas.
v 150
years ago: Settlers arrive across Oregon Trail, some crossing right through
Rock and Richardson Creek watersheds. Indian populations severely reduced in
size. Clackamas Band down to 80 people.
v 100-150
years ago: Euro-American settlers gradually clear forests of Rock/Richardson
Creeks and establish roads, villages, and farms. Extensive drain tiling
installed.
v 50-100
years ago: Area farms subdivided. Many are abandoned and return to forest
cover.
v 25-50
years ago: Post-war suburban housing boom results in population growth in Rock
Richardson Creek watersheds. Dense network of paved roads established,
including culverts that block fish migration. Nurseries and Christmas tree
farms displace food production.
v Present-25
years: Highway 212 and 224 widened. Urban development encroaches on the
westside of Rock Creek watershed. Land use planning established. Salmon listed
as threatened and Clackamas River Basin Council formed.
v See
oral histories gathered from interviews of Pleasant Valley residents in Olson,
S., et al, (2000).
v The
Damascus Historical Society and the Oregon Historic Society may have more
detailed available information.
v Interview
long time residents to research past fish occurrence, stream channelization,
and other issues.
v Contact
the Northwest Pottery Research Center (503-287-6733) to assess the location and
role of pottery industry in upper Richardson Creek.
v Examine
historic photos from the Clackamas County surveyorís office (dating from 1941)
and others made available from local residents.
Urban Growth Boundary and Urban
Reserves
Channel habitat types are stream segments that have similar
characteristics. These include gradient, or slope of the stream channel, shape
of the valley and channel that confines the stream, the pattern of the channel,
where it is located, and the structure of the stream bed. By understanding the
nature of each section of channel, we can better understand how it carries
water, what sort of habitat it should produce, and how it is affected by
sediment or other inputs. By understanding the channel habitat type, it is
possible to develop an approach to restoration or protection that matches the
natural capability of each stream or stream segment.
Channel habitat types (CHT) are classified into standard
descriptions. The OWEB
manual identifies 14 standards channel classifications. Of these, eight have
been identified for Rock and Richardson Creek watersheds, as shown on the
accompanying map of Stream Channel Types. These eight types are listed below.
v Low
Gradient Confined (LC)
v Low
Gradient Moderately Confined (LM)
v Low
Unconfined Small Stream (LUS)
v Moderate
Gradient Headwater/Moderate Gradient Confined (MH/MC)
v Moderate
Gradient Headwater/Moderately Steep Narrow Valley/Bedrock Canyon (MH/MV/BC)
v Moderate
Gradient Moderately Confined (MM)
v Steep
Narrow Valley/Bedrock Canyon/Moderately Steep Narrow Valley (SV/BC/MV)
v Very
Steep headwater (VH)
Consultants for Metro mapped CHTs in early 1999 using GIS
software, USGS elevation models, and interpretation from maps. Classifications
assigned were not field verified. Spot-checking by Ecotrust indicates that some
of the stream gradient calculations by Metro may overstate the steepness of
streams and should be used with caution.
A natural resources technical memorandum developed by URS
Corporation and recently released during the course of this assessment provides
more detailed observations of stream channel conditions for some of the
individual reaches and tributaries in both Rock and Richardson Creek (Wolfe, K.
et al, 1999, pgs. 5-9).
v The
expected historic width and character of riparian vegetation correlated to
Channel Habitat Types is unknown.
v Actual
substrate expected for each CHT is lacking.
v Accuracy
of CHT mapping is unknown.
v Field
verification of CHT map, including substrate sampling.
v Research
or analysis of historic riparian zone width for each CHT in these watersheds.
(Note: it is possible that other watershed assessments in the State may have
accomplished this already.)
Stream Channel Types
The Clackamas River Basin is one of two basins where wild coho
spawn in the Lower Columbia Endangered Species Unit. Both Rock and Richardson
Creeks have populations of anadromous and resident salmonids, as well as a
number of other fish species. While these populations are small and localized
they are regionally unique within an urban growth boundary and in an urbanizing
area. Moreover, coho is a candidate species for listing under the ESA, and it
is critical to protect all existing habitats. Stream surveys (ODFW 1999,
Dewberry 1999) have noted the presence of a number of fish species in both
watersheds, although Richardson Creek has not been as actively surveyed as Rock
Creek.
Fish Presence by Watershed
|
Rock Creek
Watershed
|
Richardson Creek
Watershed
|
|
Anadromous Fish
|
Anadromous Fish
|
|
Winter Steelhead (Oncorhynchus mykiss )
|
Winter Steelhead (Oncorhynchus mykiss )
|
|
Coho (Oncorhynchus kisutch)
|
Coho (Oncorhynchus kisutch)
|
|
Chinook (Oncorhynchus tshawytscha)
|
Chinook (Oncorhynchus tshawytscha)
|
|
|
|
|
Resident Fish
|
Resident Fish
|
|
Cutthroat Trout (Oncorhynchus clarki clarki)
|
(detailed fish survey has not been done on
|
|
Speckled Dace (Rhinichthys
osculus)
|
Richardson Creek)
|
|
Largescale Sucker (Catostomus
macrocheilus)
|
|
|
Red Side Shiner (Richardsonius
balteatus)
|
|
|
Reticulate Sculpin (Cottus
perplexus)
|
|
|
Longnose Dace (Rhinicthys
cataractae)
|
|
|
Pacific Lamprey (Lampetra
tridentata)
|
|
|
W. Brook Lamprey (Lampetra
richardson)
|
|
|
Northern Pikeminnow (Esox
Lucieus)
|
|
|
Torrent Sculpin (Cottus
rhotheus)
|
|
|
Pumpkinseed (Lepomis
gibbosus)*
|
|
|
Bullgill (Lepomis
macrochirus)*
|
|
|
Largemouth Bass (Micropterus
salmoides)*
|
|
|
Brown BullheadÝ (Ictalurus nebulosus)*
|
|
* introduced species
Both natural and human barriers limit the distribution of
salmonids. In Rock Creek a 20 foot waterfall lies about six tenths of a mile upstream
of the creek mouth. Anadromous fish make use of the area below the falls for
spawning and rearing. In-stream barriers in lower Rock Creek may inhibit
movement during low flow periods. Two small tributaries below the falls also
provide some limited habitat, although culverts just upstream block these. In
middle Rock Creek, resident cutthroat trout have been found in a stretch of the
mainstem between Foster Road and SE 172nd Avenues. These fish may be
hemmed in by culvert blockages both upstream and down.
Lower Richardson Creek anadromous and resident salmonid
populations range from the mouth of the Creek up one and a half to two miles. A
debris dam caused by a slope failure is located about six tenths of a mile
above highway 224 and may be temporarily or partially blocking upstream fish
migration.
The Salmonid Distribution map shows the location of these
barriers along with location and distribution of salmon and cutthroat trout.
The distribution of salmonids shown on this map indicates actual known salmonid
presence based on in-stream survey work.
Studies by ODFW (1999) and Dewberry and Adams (1999) both
indicate that habitat quality is marginal to moderately impaired in lower Rock
Creek. The index of biological indicators (IBI) survey by Dewberry and Adams
(1999) found low macroinvertibrate biodiversity in 1997, although numbers were
much higher in 1998. ODFW (1999) noted a series of existing conditions that can
cause problems for salmonids, including the following.
v Low
dissolved oxygen
v High
summer water temperatures
v Limited
spawning gravels
v High
sediment loading
v Low
summer flows
v High
seasonal flows
v Limited
refuge habitat
v Low
frequency of pools
v Low
levels of large woody debris
v Low
levels of hiding cover
A lower Rock Creek snorkel survey conducted in July 2000 by
Ecotrust found marginal visibility in pools and high algae production
(indicating high temperatures and possibly low dissolved oxygen during early
mornings). There were high populations of Shiners and Dace (which are more
tolerant of high water temperatures), but no juvenile anadromous salmonids were
found.
The middle section of Rock Creek that contains resident cutthroat
trout appears to be quite marginal habitat, though water quality tests were not
conducted in this area. Nevertheless visual surveys indicate poor riparian
cover, partly channelized stream sections, a lack of habitat complexity and a
lack of refuge habitat.
Lower Richardson Creek appears to have better habitat than does
Rock Creek. The snorkel survey conducted in July 2000 by Ecotrust focused on a
section from Highway 224, upstream about one mile. The survey noted adequate
visibility and a healthy riparian zone with good pool and riffle presence. Coho
salmon, trout, cutthroat trout, and steelhead were identified, but there was a
lower number and density of anadromous salmonids than might be expected. The
slump and logjam in this section currently forms a partial barrier to upstream
migration.
Department of Fish and Wildlife fish surveys and habitat analysis
for Richardson Creek noted the presence of anadromous salmonids in Reach 1,
which extends from the mouth of Richardson Creek upstream to where the
stream branches into three tributaries, southwest of SE Barlow Court. URS
Corporation, in their work on the Master Stormwater Plan for Clackamas County
concluded that salmonids in Richardson Creek are primarily confined to Reach 1
due to a combination of factors including low summer flows, heavy sediment
loading, substantial channelization of creek sections, numerous culverts
(including an impassable one at Barlow Road), and a lack of in-stream habitat
structure (Wolfe et al, 1999).
Rearing habitat for salmonids appears to be limited to Reach 1.
While suitable, these conditions are below optimal due to low summer and fall
flows, low frequency of pools, low pool depth, lack of adequate spawning
substrate, and low in-stream cover.
Ecotrustís survey and analysis suggests that there are three
critical areas or ìhot spotsî for salmonids in Rock and Richardson Creeks.
These include (1) Lower Rock Creek, from the mouth up to the falls, (2) Middle
Rock Creek, from SE 172nd east to Foster Road, and (3) Lower
Richardson Creek. These areas all have confirmed salmonid populations and offer
good potential for habitat restoration and species recovery. Two of the three
have decent riparian zones and relatively good habitat. These three areas
should receive special attention in terms of monitoring, protection, and
restoration. If salmon cannot be retained in these sections, then they cannot
continue to exist in these watersheds.
The URS Corporation natural resources technical memorandum
provides additional observations on fish populations and habitat quality for
some of the individual reaches and tributaries in both Rock and Richardson
Creek (Wolfe, K. et al, 1999, pgs. 12-21).
Metroís draft Rock and
Richardson Creek Landscape and Natural Resource Assessment includes a map (Map
8) of relative landscape values for fish habitat based on relative values
(Apostol, et al, draft). While not based on empirical data this map indicates
general areas that may have potential to support quality fish habitat.
v Historic
levels of salmonid populations in Rock and Richardson Creeks.
v Develop
a more detailed field assessment of culverts to identify migration barriers.
v Continue
the IBI surveys in lower Rock and Richardson Creeks. Begin IBI surveys in the
Middle Rock creek hot spot.
v Continue
annual summer snorkel monitoring in Rock and Richardson Creeks.
v Begin
efforts to reach landowners and public officials with an aim of implementing
measures to protect the three critical hot spot areas.
v Interview
long time residents to research past fish occurrence (see Olson et al, 2000).
Salmonid Distribution
Stream sediment results from erosion that may be part of a
natural process or one influenced by cultural activities. It can be deceptively
difficult to identify sediment sources and to distinguish natural from
human-caused sources. Potential sources of erosion and sedimentation can be
visually identified as gullying, landscape scars, road and bridge washouts, and
risky cultural practices such as till agriculture on steep slopes. The relative
risk of erosion can also be predicted as a function of soil type, slope and
other factors.
No comprehensive data on sediment sources in Rock or Richardson
Creeks were available for this assessment. Moreover, the ongoing stormwater
study commissioned by Clackamas County Water Environment Services is not
intended to comprehensively address erosion or stream sedimentation.
Stream sedimentation is a significant issue in parts of these
watersheds, and high levels of silt, sand and fine organic matter may adversely
impact successful spawning of both salmonids and lamprey in some areas (ODFW,
1999). Excess sedimentation was observed in lower Rock Creek, and is considered
to be one of several factors creating sub-optimal salmonid habitat below the
falls in Reach 1 (Fowler and Davis, 2000). Limited field observation indicates
gully and surface erosion occurring in the steeper slopes of the Prairie
Terrace zone west of Damascus currently under till agriculture, and in the
steeper road-side ditches in the upland areas of Rock creek watershed as seen
along Foster Road. Bank erosion and silt deposition is particularly significant
in Reach 5 of Rock Creek (Wolfe, K. et al, 1999). Bank erosion in this
particular portion of Rock Creek is degrading potential spawning and rearing
habitat for cutthroat trout. Bank instability has been aggravated by the
removal of riparian cover in this reach. Some bank erosion is also apparent in
Upper Richardson Creek. The lack of adequate riparian buffers and vegetation in
the upper reaches of both watersheds poses a risk of future sedimentation.
Soils and elevation were used to develop the map of Steep Slopes
and Erosion Hazards, showing slopes greater than 25 percent and soils rated with
a high erosion potential by the Natural Resource Conservation Service. The
lower canyon areas of both Rock and Richardson Creeks include considerable
overlap between steep slopes and high erosion potential soils. The mid-slope of
the Boring lava domes in northeast Rock Creek watershed and northern Richardson
watershed are also characterized by steep slopes.
The potential for stream sedimentation in both watersheds to
increase in the future is quite high. A model developed by URS Corporation to
estimate pollutant and sediment loads under future urbanization indicated a
six-fold increase in suspended sediment loads (Wu and Fowler, 2000).
The channel condition assessment in the URS Corporation natural
resources technical memorandum provides some specific information on individual
reaches and tributaries in both Rock and Richardson Creek relative to potential
sediment sources (Wolfe, K. et al, 1999, pgs. 5-9).
v Empirical
data on erosion and stream sedimentation is lacking.
v The
relationship between observed erosion and stream sedimentation is unknown.
v Ancillary
data necessary to assess sedimentation, such as peak stream flows, debris flow
potential and landslide inventories, are lacking.
v The
impact of new impervious surfaces and urbanization more generally on
sedimentation has not been analyzed.
v Work
with interested residents and landowners to identify visible erosion sites and
cultural practices that may lead to sedimentation.
v Work
to educate residents, landowners, and developers on best management practices
to limit erosion and sedimentation and develop local groups to monitor
activities.
v Work
with appropriate planning agencies and landowners to protect areas with steep
slopes and high erosion potential soils through maintenance and enhancement of
stabilizing forest cover.
v Encourage
tree planting in sensitive riparian zones.
Steep Slopes and Erosion Hazards
Riparian and wetland areas are two of the most critical elements within
watersheds that influence the health of the aquatic ecosystem. As mentioned in
the History section, Douglas-fir forests characterized much of Rock and
Richardson Creek watersheds prior to Euro-American settlement. Riparian areas,
or the vegetation zone that influences stream conditions, varied in width
depending on the stream channel type and surrounding topography. For the
purposes of this analysis, we have assumed a uniform width of 200 feet on
either side of streams, regardless of channel type.
The characteristics of riparian vegetation within Rock and
Richardson watersheds can be described in terms of three general geomorphic
zones: (1) the upland lava dome and first order streams, (2) the valley floor
second and third order streams, and (3) the lower creek canyon mainstems and
floodplain.
The lava dome upland riparian zones are mostly forested, with
second or third growth deciduous and coniferous trees in the overstory, mostly
alder, maple, and Douglas-fir. Tree canopy ranges from 30 to 90 feet in height.
Understory plants include hazel, dogwood, and blackberry brambles. In some
areas, roads wind along these streams (Borges, Tillstrom) and thus disrupt the
riparian cover. A utility corridor on Scouter Mountain cuts across the riparian
zones of two upland creek sections. Culverted driveway crossings are numerous,
particularly in the hills east of Pleasant Valley. In other areas, particularly
in upper Richardson Creek tributaries, pastures and fields come right to the
edge of streams.
The valley floor riparian areas are only moderately forested.
Agriculture, subdivisions, golf course construction, and roads have heavily
altered the valley floor riparian zones. Generally, these areas are
characterized by a narrow (10 to 30 feet) band of shrubs and small trees
(willow, dogwood, ash, and blackberry). Sections of valley streams have been
channelized, further impacting the riparian zone. Some areas have no riparian
cover at all, including parts of the golf course, the stream that flows through
Damascus, and several stream sections in Pleasant valley. Other areas have
orchards, nurseries, and berry fields crossing right over streams.
The lower creek canyon mainstems of both Rock and Richardson
Creeks are mostly forested. This forest is fairly mature, and even includes
individual old growth conifers, as well as cottonwood, alder, maple, and oak.
The riparian zone of lower Richardson seems to be of higher quality than that
of Rock, but both are in fairly decent condition. The floodplains along the Clackamas,
at the mouth of both creeks, also have mostly forested riparian zones.
The table below showing riparian zone vegetation is a summary of
vegetation types within 200 feet of all streams in the two watersheds. The
200-foot zone is an arbitrary estimation of the true riparian area. The land
cover map data used for this analysis is designed for regional analyses and is
not appropriate for assessments of stream shading or in-depth local riparian
characteristics. Nonetheless, this broad analysis provides a rough picture of
riparian conditions. The map of Land Use and Land Cover shows the distribution
of broad vegetation and cover types across the entire landscape.
Riparian Zone Vegetation
Characteristics by Watershed *
|
Land
cover
|
Rock
Creek
|
Richardson
Creek
|
|
|
acres
|
percent total
|
acres
|
percent total
|
|
Urban / built up
|
121
|
9.10
|
58
|
9.30
|
|
Agriculture
|
|
|
|
|
|
ÝÝ Low structure agricultural
|
316
|
23.88
|
100
|
16.10
|
|
ÝÝ High structure agricultural
|
14
|
1.03
|
27
|
4.40
|
|
Forest
|
|
|
|
|
|
ÝÝ Closed canopy deciduous
|
239
|
18.02
|
38
|
6.11
|
|
ÝÝ Closed canopy mixed
|
261
|
19.70
|
215
|
34.41
|
|
ÝÝ Closed canopy coniferous
|
28
|
2.11
|
20
|
3.18
|
|
ÝÝ Open canopy deciduous
|
56
|
4.20
|
39
|
6.33
|
|
ÝÝ Open canopy mixed
|
74
|
|
