Introduction *

Maintenance Chronology (Task 5) *

Strategies for Long-term Monitoring and Maintenance 35

Long-term Conceptual Recommendations (Lessons Learned) 38

References *

Table 1. Land use in the Morro Bay Watershed *

Table 2: Estimated Sediment Loads to Morro Bay from Chorro Creek *

Table 3: Sediment capture on Chorro Flats, 1992-1998, by particle-size *

Table 4. Estimates of Project Longevity *

Table 5. Plant Survival Summary *

Table 6. 1999 MAPS Captures at Chorro Flats *

Table 7. Desired Monitoring Activities *

Table 7. Desired Monitoring Activities (continued) *

Figure 1: Vicinity Map *

Figure 2: Site Plan *

Figure 3: Aerial Photo of Site and Vicinity *

Figure 4: Simplified Chorro Flats fluvial processes, pre- and post-construction *

Figure 5: Typical Plant Maintenance Procedure, May – June, 1998 *

Figure 6: Willow Mattress - During Installation, May 1998, and after 4 months. *

Figure 7. CCCs installing a willow baffle, September, 1998. *

Figure 8. Irrigation continued in 1999. *

Figure 9. Willow wattles installed in 1999. *

Figure 10. Replanting in November, 1999. *

Figure 11. Willow mattress installation 1999. *

Figure 12: Instream Habitat Improvement Structures Installed in 1999. *

Figure 13. Instream habitat structure installation, 1999. *

Figure 14. Opposing wing deflector after installation. *

Figure 15: Monthly precipitation between July 1992 and June 1998. *

Figure 16: Comparison of 1992 Elevations to 1998 Elevations. *

Figure 17. Upstream end of "overflow" channel. November 1997. *

Figure 18. "Overflow" channel at upstream end of project. February 1998. *

Figure 19. Chorro Creek at upstream end of project. January 2000. *

Figure 20. Cross-section locations *

Figure 21. Cross-sections from the upstream portion of the project *

Figure 22. Cross-sections from the downstream portion of the project *

Figure 23. Cross-sections from the old channel of Chorro Creek *

Figure 24. Cross-sections from overflow channel "B" *

Figure 25. Existing and designed channel bottom profile *

Figure 26. Existing and designed channel capacity *

Figure 27. 1998 maximum daily upstream and downstream temperatures *

Figure 28. 1999 maximum daily upstream and downstream temperatures *

Figure 29. Groundbreaking Ceremony July 9, 1997 33

Figure 30. Dedication Ceremony held 10-09-98 34

Figure 31. Lot Line Adjustment *

Figure 32. Alternative Location for Channel Connection and Berm *

The Chorro Flats Enhancement Project was implemented to reduce sediment loads to Morro Bay by allowing Chorro Creek to overflow on its original floodplain. The project has restored and enhanced 83 acres of wetland and wildlife habitat. The remaining 45 acres of prime farmland are used for agricultural production.

This report summarizes site acquisition, planning, construction, maintenance and monitoring associated with the project, and serves as a "final report" for a grant administered by the Central Coast Regional Water Quality Control Board.

A study conducted in 1988 showed that Morro Bay had been filling in at a rate ten times greater during the last one hundred years than it had previously. The major source of the sediment is the brushlands in Chorro and Los Osos Valleys.

The Coastal San Luis Resource Conservation District, using funds provided by the California State Coastal Conservancy and Cal Trans, purchased the Chorro Flats site in 1991. Consultants prepared an Enhancement and Management Plan for the site. During all phases of the planning process extensive public input was encouraged.

In 1994, a fire burned 35% of the Chorro Creek watershed in the steep brushy areas of the Santa Lucia Range. The Natural Resources Conservation Service improved the sediment trapping capability of Chorro Flats by creating a 450 foot breach of the levee. The most extreme floods of record followed this major fire the following winter, resulting in significant sediment deposition on Chorro Flats.

The State Water Resources Control Board, the California Coastal Conservancy, and Cal Trans provided funding for construction and maintenance costs. Work began in July of 1997, and was completed in late November.

During the El Niño winter of 1997-98, the entire site was repeatedly flooded, and significant amounts of sediment were deposited on the site. This first-year deposition, when combined with the deposition from the 1995 floods and all the other minor floods since 1992, brought the net total amount of sediment captured on the site to 188,000 cubic yards.

During early 1998, approximately 12,000 cubic yards of fine grained material (equal to about 6% of the net amount collected on site between 1992 and 1998) eroded from the banks of the upstream portion of the newly installed overflow channel. This erosion lowered the thalweg of the overflow channel so that the majority of the flow in Chorro Creek now passes through the overflow channel, with the old creek channel now acting as an overflow channel.

In 1998, the California Conservation Corps performed the initial maintenance on planted materials: checking each plant location and condition, hand weeding, clearing, building irrigation basins, watering, and placing mulch. Other maintenance activities have included installation of "willow mattresses" and other riparian tree species by CalPoly students, application of herbicide to control undesirable weed species, replanting of some grasslands, periodic mowing of the grasslands, and additional willow plantings along the banks of the creek. Additional trees and shrubs were installed in late 1998 and late 1999 to replace plants that had not survived. Raptor perches have been installed within the riparian zone along Chorro Creek to enhance rodent control.

During September and October 1999, 12 log and boulder structures were installed in the upstream portion of the project to improve steelhead trout summer rearing habitat. The work was partially funded by a $30,000 CDFG fisheries restoration grant.

Approximately 23% of the total load, and 85% of the bed-load, from Chorro Creek between 1992 and 1998 was captured on Chorro Flats. The current estimate for sediment loads from the watershed is more than twice the estimate used in 1993. Based on the revised annual sediment load, and the 23% trapping efficiency, it is expected that the Chorro Flats site will fill in 26 years.

Any actions upstream of the Chorro Flats Enhancement Project that reduce sediment loads to the creek will also serve to enhance the longevity of this project. Specific actions could include implementation of additional best management practices for sediment control or development of additional sediment trapping areas (mini-Chorro Flats) further upstream.

The stream is developing a dynamically stable configuration. First-winter changes were significant. Second-winter changes were much smaller. Future annual changes are expected to be small because the banks are more thickly vegetated and therefore more stable, and because the first-winter changes significantly increased the flow capacity of the channel.

In July and August, of 1998 and 1999, a survey of the planted areas was conducted. The riparian plant community is developing. Willow growth exceeds expectations. Other riparian plant species are growing and will soon be large enough to persist without additional maintenance.

Habitat suitable for endangered species is being created. Pools and riffles are developing. Steelhead and red-legged frogs have been found on the site. Water temperature in Chorro Creek at the upstream and downstream ends of the project were measured in 1998 and 1999. In both years, downstream temperatures are generally higher than upstream temperatures. This increase is generally between 3 and 5 ° F, with a maximum increase of almost 8 ° F. A Monitoring Avian Productivity and Survivorship (MAPS) monitoring station was set up on the Chorro Flats site in 1999. Initial results indicate that the site provides habitat for a wide variety of birds.

Numerous public education opportunities have been provided at the site, via the media, and via various public forums.

It is expected that within the next two years a suitable agency will be identified and will agree to assume ownership and responsibility for the maintenance of the wetland portion of the site.

Numerous suggestions are presented regarding lessons learned during the project. The suggestions focus on the planning process, the contracting process, alternative locations for the channel and the berm, and ways in which an "adaptive management" approach could have benefited the project.

This document and additional information regarding conservation projects undertaken by the Coastal San Luis Resource Conservation District can be found on the web at www.coastalrcd.org.

The Coastal San Luis Resource Conservation District

Precisely what is Coastal San Luis Resource Conservation District and what are its purposes? The following is a history of Coastal San Luis Resource Conservation District.

The devastation of the Dust Bowl in the 1930’s led to the passage of the federal Soil Conservation Act of 1935 It's purpose was to provide conservation assistance to ranchers, farmers and other private landowners. This federal legislation enabled states to act locally. Today there are nearly 3000 conservation districts nationwide to conserve land, water, forests, wildlife and related resources. The USDA Soil Conservation Service is now the Natural Resource Conservation Service and works in partnership with Conservation Districts.

In California the establishment of Resource Conservation Districts (RCDs) began in 1938 under Division 9 of the California Public Resource Code. The Governor, the Resources Agency and the Department of Conservation are responsible for the administration of Division 9.

The Arroyo Grande RCD was established in 1953. The AGRCD Charter Members were: Edwin M. Taylor, Manuel F, Silva, Ed. Campodonica, Keith A. Rapp and Lester Sullivan. The flooding of the farmland from the Arroyo Grande Creek was a yearly occurrence and these farmers worked tirelessly to solve the problem. Under Division 9 they received technical assistance from the Soil Conservation Service (USDA).

In 1961, about 205,000 acres south of the district were annexed, and in 1978, about 180,000 acres north of the district were annexed and the name of the was changed to Coastal San Luis RCD. The total land area in the district is 463,024 acres. The land ranges from Class 1 prime agriculture soils to Class VIII soils.

The Directors of the Coastal San Luis RCD are elected by district voters or appointed by the County Board of Supervisors, and they are not compensated for their work. The Board of Directors can make legal agreements with county, state and federal governments for work in the district. Associate directors may be appointed by the CSLRCD to assist in special areas of interest. Consultants and other individuals with special expertise may be called upon to achieve conservation goals. A characteristic unique to Resource Conservation Districts is their ability to work directly with landowners on private lands.

The goals for CSLRCD are:

1. Coordinate efforts to prevent and reduce soil erosion. 
2. Improve agricultural water supply utilization. 
3. Preserve, protect and help secure grants for the protection of prime farmlands. 
4. Promote the conservation and protection of important natural habitats and ecosystems

Purpose of the Project

The purpose of the Chorro Flats Enhancement Project is to improve water quality entering Morro Bay by reducing sediment flowing into the bay from Chorro Creek by allowing Chorro Creek to overflow on its original floodplain to provide "passive" sediment capture from Chorro Creek. The project will also restore and enhance wetland and wildlife habitat, provide some public education opportunities, and continued agricultural operations which will emphasize environmentally sensitive agricultural practices.

Scope of the Project

The project has been implemented on a 129-acre site situated along Chorro Creek. 83 acres of the site have been converted to floodplain and wildlife habitat areas. The remaining 45 acres of prime farmland are used for agricultural production.

Site Development

Figure 1: Vicinity Map

Setting

Located in San Luis Obispo County, Morro Bay has been called the most biologically important estuary on the Central Coast (Arnold, 1991). Morro Bay is approximately four miles long and about one and three quarters miles wide at its maximum width. At high tide Morro Bay consists of approximately 2300 acres of open water (Haltiner,1988).

The watershed of Morro Bay is approximately 48,450 acres and is bounded by the Santa Lucia Range on the north, Cerro Romauldo to the east and the San Luis Range to the south. Eventually draining to Morro Bay, the watershed houses two significant creek systems: Los Osos and Chorro Creeks. The Chorro Creek watershed drains approximately 27,670 acres, while Los Osos Creek drains 16,933 acres, the remaining area drains directly into the bay through small local tributaries or urban runoff facilities. Sixty percent of the Chorro Creek watershed is classified as rangeland, while twenty percent is brushland. Table 1 displays the land use in the Morro Bay watershed

.Table 1. Land use in the Morro Bay Watershed

Land Use	Acres
Cropland/Hayland	3,149
Pasture (Irrigated/Domestic)	49
Rangeland	26,162
Forest/Woodland	3,093
Chaparral	8,516
Urban	3,389
Other	4092
Total acres in watershed	48,450

 

Problem Identification and Watershed Planning

Erosion in the watershed was seen as a problem by many observers through the years. The Coastal San Luis Resource Conservation District (RCD) had long recognized the importance of the Morro Bay Estuary. In the 1970's District leaders adopted the reduction of erosion in the Morro Bay watershed as one of their long term goals. In 1987 the RCD obtained funding through the California State Coastal Conservancy (SCC) to quantify the historical loss of open water in the bay, and to locate and quantify sediment sources to the bay in order to create a baseline for future reference. The results of the study indicated that the bay had been filling in at a rate ten times greater during the last one hundred years than it had previously (Haltiner, 1988). The results also showed that the bay has decreased in volume by 25 percent in the last century (Haltiner, 1988). The major source of the sediment is the brushlands in Chorro and Los Osos Valleys. Chaparral covers approximately 19% of the 48,450 acre watershed. However, it contributes 30% of the sediment to the bay. Conversely rangeland covers 60% of the watershed, yet contributes only 17% of the sediment to the bay (USDA SCS, 1989).

Using these studies as a baseline the RCD then hired the USDA Soil Conservation Service (now known as the Natural Resources Conservation Service) to develop the Morro Bay Watershed Enhancement Plan. The recommended plan detailed three phases of action. Phase I was land treatment. Phase II was a sediment trap on Los Osos Creek. Phase III was a sediment trap on Chorro Creek.

Phase III of the Mbwep is the Chorro Flats Enhancement Project (CFEP): which is a sediment capture, agricultural preservation, habitat restoration and education project. The CFEP has essentially reconnected Chorro Creek with its historical floodplain, thereby allowing sediment to be deposited there instead of in Morro Bay. This is the most significant single action included in the plan. It was estimated that 35% of the sediment entering the Bay through Chorro Creek could be caught by a sediment trap at this site (USDA SCS, 1989).

Site Description

The 129 acre site located at the intersection of Quintana Road and South Bay Boulevard near the city of Morro Bay was once known as Chorro Cienaga (swamp). At that time, under the dense vegetation of willows and other riparian species, when Chorro Creek flooded, the water spread over the land and dropped sediment. Rich alluvial soils were created by this process and millions of cubic yards of sediment were trapped here rather than being carried into the bay.

In the 1950’s Chorro Creek was confined by a levee to a narrow channel along the southern edge of the property. This allowed the adjacent land to be used for growing vegetable and hay crops in the rich stream deposited soils. But the sediment-rich water flowing downstream was no longer able to spread out and deposit its load on the floodplain as it had been doing for eons. Instead, the sediment remained suspended until it reached the estuary, where much of it was trapped.

Figure 2: Site Plan

Site Acquisition

The Morro Bay Watershed Enhancement Plan recognized that the Chorro Flats site would be an ideal place to trap sediment before it reached the Bay. Fortunately, about that time the Domenghini family that had owned and farmed the site for years put the land on the market. Carol Arnold of the State Coastal Conservancy entered into negotiations with the family, and after two years of on-again off-again negotiations entered into an agreement with the owners to purchase the land. Carol Arnold put together a package where the Conservancy would provide funds to the RCD to acquire and restore the site. The purchase price of $1,450,000 required more funds than those available to the SCC at that time, so Ms. Arnold applied for and received $800,000 from Proposition 111 funds, administered by Cal Trans. The RCD received the title for the land on December 18, 1991, and immediately began the planning process for the CFEP.

Figure 3: Aerial Photo of Site and Vicinity

 

Project Planning

The Chorro Flats site is especially suitable for sediment trapping because:

• Chorro Creek runs through the site; 
• Chorro Flats is at the terminus of the watershed; 
• Chorro Flats is relatively flat and well suited to trap sediment; 
• The site historically was a floodplain, covered with riparian vegetation that naturally trapped sediment.

Sediment control was the principal reason behind the acquisition of the property, however the RCD and the SCC recognized that a number of other important natural resources on the site could be protected and enhanced. These resources include the aquatic habitat and fisheries, the riparian habitat and wildlife, groundwater, agricultural use and water quality and quantity.

After receiving another grant from the Coastal Conservancy, the RCD hired consultants to prepare an Enhancement and Management Plan for the site. Several preliminary studies preceded the preparation of the final plan. The first report was an assessment of the planning area covering topography, hydrology, groundwater, soils, agriculture, vegetation, wildlife, fisheries, archeology, easement, and regulatory polices applicable to the site. The results of this study were published in the Existing Conditions Background Report.

During all phases of the planning process extensive public input was encouraged. Several public meetings were held. The Morro Bay Task Force was involved in the planning process. A Technical Advisory Committee composed of members of the public, the California Department of Fish and Game, the State Department of Parks and Recreation, the Regional Water Quality Control Board, the County of San Luis Obispo, the City of Morro Bay, the U.S. Fish and Wildlife Service, the Army Corps of Engineers, the SCC, the NRCS, the National Estuary Program, the Sierra Club, the Friends of the Estuary and neighbors of the site met on a regular basis to discuss and decide on issues.

Next, specific goals and objectives for the plan were articulated. These related to sediment trapping, agriculture, fisheries and wildlife enhancement among other topics and are published in a report entitled Goals and Objectives for Chorro Flats.

The consultant team developed three alternatives for the site. These alternatives were considered and discussed at a number of public meetings. Alternative one emphasized agriculture and devoted more of the site to that purpose. Alternative two increased the size of the floodplain, while still maintaining a viable agricultural parcel on a portion of the site best suited for farming. The third alternative included an active sediment removal basin that would require periodic dredging of a sediment basin located off the main channel of Chorro Creek. This alternative would have resulted in some negative impacts related to fisheries, maintenance costs and aesthetics.

These alternatives were presented in the Analysis of Options and Alternatives Report, and they were discussed at a number of public meetings. The public and the Technical Advisory Committee overwhelmingly favored alternative two. The final plan was based on this alternative although adjustments and refinements occurred in the final detailed planning. The final plan was published in April of 1994 and was titled: Conceptual Plan, Chorro Flats Enhancement and Management Plan.

The passive sediment trapping system allows sediment to accumulate on the floodplain as a result of deposition during overbank flows. Increased vegetation on the floodplain helps to reduce the velocity of overbank flows and increase the rate of sediment deposition. Approximately 83 acres were included in the floodplain and 45 acres were reserved for agriculture. This allowed for a capacity of in excess of 600,000 cubic yards and a projected lifespan of at least 50 to 70 years. The deposited sediment will primarily be sand sized particles with a moderate amount of fine grained materials (silt and clay). Most of the coarse grained material (pebble and cobble) will be trapped in the creek channel. See Figure 4.
  

Figure 4: Simplified Chorro Flats fluvial processes, pre- and post-construction

 

Interim Site Development

Not long after the completion of the Conceptual Plan, the August 1994 "Highway 41 Fire" erupted. The fire burned 9700 acres, or 35% of the Chorro Creek watershed. The area that burned was the steep brushy areas of the Santa Lucia Range (Cuesta Ridge). Slopes as steep as sixty percent were left denuded of protective vegetation. The RCD took advantage of a federal program administered by the NRCS called Emergency Watershed Protection (EWP). An EWP project was completed at Chorro Flats. To reduce the potential for sediment conveyance to Morro Bay, the NRCS improved the sediment trapping capability of Chorro Flats by creating a 450 foot breach of the levee and stockpiling the material in a berm perpendicular to the channel.

In an exceptionally rare combination of extreme events, this major fire was followed by the most extreme floods of record the following winter. In mid-January and again in mid-March intense rainstorms produced tremendous flows in Chorro Creek. The 2 to 3 day rainstorms producing these flows had a recurrence interval of between 100 and 1000 years (Jim Goodridge, former State Climatologist). Flood debris left on the radio towers at Chorro Flats was more than thirteen feet above the ground surface.

It should be recognized that the sediment trapping that occurred on the site following the 1995 floods represented a significant benefit to Morro Bay and provides validation for the acquisition of this site. It also presented an opportunity to further refine the conceptual plan. A geomorphic review team recommended that the existing Chorro Creek alignment be allowed to remain as the primary flow channel. They further recommended that the primary restoration approach should be to remove the existing levee, construct a new berm far away from the channel and excavate a shallow swale to encourage some channel overflow and provide a secondary channel location for the inevitable channel avulsion.

The location of the overflow channel was modified so that the connection to Chorro Creek would occur at Chorro Creek Road. This location scoured severely following the high flows of the early and mid 90's, indicating that geomorphically, this was an alignment the channel wanted to take. Additionally, the ecologic impact and permitting issues were easier here, as there were fewer trees and impacts. Also, it made better use of the upstream and higher elevations of the site for sediment capture.

Project Implementation

Design In 1996 work began on the final working drawings and the specifications for the construction contract. Plant ecologists and restoration specialists worked on developing the planting program. Only plants native to the watershed were selected. The planting was to be done in bands adjacent to the new channels in order to promote the riparian corridor and get it established prior to the expected channel avulsion. The ground in between the plants and the wide areas beyond the planting zones were to be planted with native grasses. The final plant count was over 10,792 plants including 211 Red-osier dogwood trees, 431 California sycamores, 845 Black cottonwoods, 72 Coast live oaks and nearly 8900 red and arroyo willows. Additionally, wax myrtle, coffeeberry, gooseberry, California wildrose, blackberry, twinberry, hummingbird sage and elderberry were selected. The native grass mix included California brome, blue wildrye, meadow barley and creeping wildrye.  Additional Funding The RCD also applied for funding from the State Water Resources Control Board and was granted $300,000 for construction and maintenance of the project. Carol Arnold and the Coastal Conservancy once again came through with funding to implement the project. Carol applied for and received $300,000 from Cal Trans, and the Coastal Conservancy contributed $170,000 toward the construction and maintenance costs.  Permits After a lengthy and interesting process of acquiring all the needed permits from the permitting agencies including; the County of San Luis Obispo, the City of Morro Bay, the Army Corps of Engineers, the Department of Fish and Game, the U.S. Fish and Wildlife Service, the National marine Fisheries Service, the Regional Water Quality Control board and the Air Pollution Control District the CFEP was ready to go out to bid.  Construction Whitaker Contractors of Santa Margarita was the contractor selected to construct the project. Work began in July of 1997, five and one-half years after the RCD acquired the land. Whitaker was a very good contractor and the work proceeded very smoothly and was performed on time and on budget. The planting subcontractor completed the last of their work in late November of 1997. At the beginning of December when viewed from Black Hill the Chorro Flats Enhancement Project looked very much like the finished engineering drawings. 

Monitoring and Maintenance Planning

A monitoring and maintenance plan (M&M plan) was developed in 1998 by the CSLRCD, and approved in July of that year by the RWQCB, the U.S. Army Corps of Engineers, and the State Coastal Conservancy. (See Appendix A.) The M&M plan was produced to comply with permit requirements; to track and address localized problems of erosion, revegetation needs, and other modifications identified as the project matures; and to assess the overall success of the project in meeting its goals and objectives. The M&M plan specified short-term activities planned for the first two years following construction and long-term activities planned for the next five years. Long-term monitoring activities are planned to measure deposition, document channel morphology changes, and monitor riparian vegetation establishment. Long-term maintenance activities are planned to focus on establishment of riparian vegetation, promotion of stable stream banks, and maintenance of roads, berms, and other improvements. These activities will initially be funded from a combination of grants. With time, as monitoring and maintenance needs decrease, rental income from of the agricultural portion of the site and the radio towers will be used for these activities.

Maintenance Chronology

Beginning in May 1998, the California Conservation Corps (CCC) performed the initial maintenance on planted materials: hand weeding, clearing, building irrigation basins, watering, and placing mulch. The typical procedure is illustrated in Figure 5a through 5d. 

 

Figure 5a. First you must find the plant. In this case a cottonwood.

Figure 5b. Then clear away competing plants using hand tools.

 

Figure 5c. After the irrigation basin is formed, approximately 2 gallons of water are applied.

Figure 5d. The finished site includes 3 inches of mulch and a flag to aid future identification.

Figure 5: Typical Plant Maintenance Procedure, May – June, 1998

In June, Dr. Brian Dietterick and some of his resource management students from Cal Poly installed "willow mattresses" along portions of the new channel "A". See Figure 6.
 
  

Installation of the willow mattress 5-29-98.

View from same location 9-25-98.

  

View from upstream side 5-29-98.

View from upstream side 9-25-98.

Figure 6: Willow Mattress - During Installation, May 1998, and after 4 months.

In June 1998, a landscape contractor applied herbicide to control weeds (hoary cress, German ivy, and castor bean) found on site.

All of the shrubs and trees that were planted in 1997 were maintained through the summer of 1998 by periodic mowing and hand weeding, and by periodic irrigation.

In September, 1998, two sections of stream bank were intensively planted with willow fascines to enhance bank stability.

Figure 7. CCCs installing a willow baffle, September, 1998.

In October 1998 fire-breaks were mown around the grassland areas.

In October 1998 "No Access" signs were installed.

During December 1998 1087 trees and shrubs were installed by a landscape contractor.

Grassland portions of the site were mown in January, April, June, and July 1999.

During April, May, and June 1999, trees and shrubs planted as part of this project continued to receive periodic maintenance by CCC crews, as needed, including hand-weeding, mowing, basin re-building, mulching, and irrigation.

Figure 8. Irrigation continued in 1999.

In June 1999, and again in July, an herbicide (Garlon) was applied to German Ivy growing along the old creek channel, and to patches of Arundo donax, pampas grass, and castor bean found near the northern most radio tower and near the junction of the old creek and Channel B.

During June 1999, eleven raptor perches have been installed within the riparian zone along Chorro Creek, to enhance rodent control.

During June and July 1999, willow stakes were installed by CCC crews at the base of some vertical banks along Chorro Creek. The purpose of these planting is to help stabilize the banks and increase deposition.

Figure 9. Willow wattles installed in 1999.

In November 1999, 415 trees and shrubs were planted by Dave Fross’ Habitat Restoration class from Cal Poly.

Figure 10. Replanting in November, 1999.

In November 1999 two willow mattresses were installed by Brian Diettricks’ Watershed Management class from Cal Poly.

Figure 11. Willow mattress installation 1999.

Approximately 15 acres of grassland were replanted with native grass seed and mulched with rice straw in November 1999. A filter strip of native grasses was planted between the agricultural fields and the swale that drains these fields.

The remaining grasslands on site were mown in December 1999.

Revegetation efforts associated with the newly installed instream habitat improvement structures were completed in December 1999.

Due to continued dry conditions, trees, shrubs, and willow mattresses were irrigated in late November, and again in late December 1999.

Aquatic Habitat Improvement Structures

During September and October 1999, 12 log and boulder structures (5 pair of opposing wing deflectors, 1 single wing deflector, 2 mid-stream boulder clusters, and 4 log and boulder structures) were installed in the upstream portion of the project to improve steelhead trout summer rearing habitat. The work was partially funded by a $30,000 CDFG fisheries restoration grant, and followed procedures in the DFG California Salmonid Stream Habitat Restoration Manual. Rock for the project was imported from local quarries to the project site. Some root wads which were installed into the banks in 1997, and which were too high to function properly, were removed and used for this project. Additional root-wads and logs were supplied by Morro Bay State Park. Logs and large rocks were placed in the stream bed using rubber wheeled heavy equipment.

Figure 12: Instream Habitat Improvement Structures Installed in 1999.

Photographs were taken to document conditions before, during, and after construction, and will be taken again in subsequent years. See Figures 13 and 14 below. (This effort complements the photo documentation which is part of the ongoing CFEP). Each spring, the integrity and functionality of each structure will be evaluated, and each structure will be repaired or modified as needed.

Figure 13. Instream habitat structure installation, 1999.

Figure 14. Opposing wing deflector after installation.

An instream fish habitat survey was conducted by the Department of Fish and Game in the summer of 1998. Another survey will be conducted using DFG protocols in the summers of 2000 and 2002 to compare pre- and post-project conditions. (This survey work is included as part of the ongoing CFEP.)

Results of the habitat survey, and experience gained during installation and maintenance of the structures, will be used to plan additional habitat improvement structures. A CDFG fisheries restoration grant has been secured to partially fund this habitat improvement effort for an additional two years.

Monitoring Results

Monitoring activities were designed to answer the following "big" questions:

• How much sediment is being collected?

• Is a riparian plant community developing?

• Is the stream developing a dynamically stable configuration?

• Is habitat suitable for endangered species being created?

• Are beneficial uses being enhanced or is water quality being improved?

The answers to these questions are discussed in the sections that follow.

Sediment Collection

Approximately 23% of the total load, and 85% of the bed-load, from Chorro Creek between 1992 and 1998 was captured on Chorro Flats (Robbins and McEwen, 1999). This trapping efficiency was determined by

· modeling sediment loads to the upstream end of Chorro Flats; and then

· measuring the volume of sediment collected;

· using sediment samples to estimate the particle size distribution and mass of the collected material; and then

· comparing modeled sediment loads to estimated amounts of sediment captured.

Monthly precipitation from July 1992 to June 1998 is shown in Figure 15.

Figure 15: Monthly precipitation between July 1992 and June 1998.

Total sediment loads to Chorro Flats from Chorro Creek were modeled based on flow rates measured at a gage on Walters Creek, a tributary to Chorro Creek. Annual total sediment yield and bed material yield for the Chorro Creek watershed has been estimated for the 1993 through 1996 water years. Additionally, the long-term average annual total sediment yield for the watershed has been estimated to be 60,689 tons, with an average annual bed material yield of 6,980 tons (Tetra Tech, 1998). These modeled estimates are listed in Table 2.

Table 2: Estimated Sediment Loads to Morro Bay from Chorro Creek

Water Year	Estimated Total Load, tons	Estimated Bed Material Load, tons
1993	43,040	11,225
1994	277	165
1995	734,891	49,063
1996	20,777	5,294
1997	60,689*	6,980*
1998	60,689*	6,980*
Total Load	920,363	79,707

(* Long-term average values)

(**Bed material consists of particles which are larger than very fine sand particles, 0.074 mm.)

The volume of sediment which was collected on site was measured as follows. Topographic surveys were conducted in 1992 (EDA, 1997) and early 1999 (Vaughan Surveys, 1999). Comparison of this topographic data showed that approximately 188,000 cubic yards (over 213,000 tons, assuming 84 lb/cubic foot) of sediment were collected on site during this time. A topographic map comparing 1992 to 1998 elevations is shown in Figure 16. (Green indicates areas of almost no change in elevation. Warmer colors indicate the elevation lowered. Cooler colors indicate areas of elevation increases, i.e., sediment deposition.)

Figure 16: Comparison of 1992 Elevations to 1998 Elevations.

The particle size distribution of the deposited sediments was found by subjecting sediment samples to a #200 sieve wash (Earth Systems Consultants, 1998). Samples were collected from eroded streambanks, from the creek and overflow channel beds, and from the surface of the floodplain. Particle-size data were combined with topographic data to estimate the net deposition on site for all sediments, and the net deposition for bed material. These results are summarized in Table 3, and are compared to estimated sediment loads from the watershed.

Table 3: Sediment capture on Chorro Flats, 1992-1998, by particle-size

	All Sediment, tons	Bed Material , tons
Load from watershed	920,363	79,707
Deposited on Chorro Flats	213,546	68,125
Percent capture	23%	85%

These figures show that approximately 23% of the total load from Chorro Creek, and 85% of the bed-load, was deposited on Chorro Flats between 1992 and 1998. A significant amount of deposition occurred on site between 1992 and 1997 as a result of breaks in the levee, some naturally occurring, and the one enlarged in 1994 through the EWP program to collect sediment following the Highway 41 Fire. Significant deposition also occurred during the El Niño winter, just months after construction was completed.

It is expected that the long-term sediment capture rates will be larger than these values because the project wasn't completed until almost the end of this time period, and because the trapping efficiency is expected to be greater now than it was prior to project completion.

Available Storage Capacity and Project Longevity

During the planning process for the project (Crawford Multari &Starr, 1993), it was estimated that the project would have 76 acres available for sediment deposition, with a total storage capacity of 610,000 cubic yards (i.e., filled to a depth of 5 feet.). Of that 76 acres, approximately 51 acres would be readily available for sediment storage (because its elevation was below 20 ft.) and could hold 247,000 cubic yards of material (i.e., filled to a depth of 3 feet.) Assuming that 10,000 cubic yards of material would be deposited per year, the project would remain effective at collecting sediment for 61 years. It was also estimated that the project would capture 20% of the silts and clays, 90% of the sands, and 100% of the gravels and cobbles.

During the 6 years studied, it is estimated that 188,000 cubic yards of material were collected. Therefore, based on an initial capacity of 610,000 cubic yards, the site has an available capacity of 422,000 cubic yards as of 12/31/99. If the average sediment yield from the watershed is 60,689 tons per year (69,000 cubic yards) (Tetra Tech, 1998), and the collection efficiency remains at 23%, then approximately 15,870 cubic yards per year will accumulate, filling the available capacity in 26 years.

Table 4. Estimates of Project Longevity

	1993 estimate*	1999 estimate**
Area for deposition	76 acres	76 acres
Potential storage (cubic yards)	610,000	422,000
Sediment load from watershed (cubic yards per year)	27,000	69,000 (Tetra Tech, 1998)
Trapping efficiency	26%	23%
Sediment captured (cubic yards per year)	6,900	15,870
Years needed to fill site (based on 1993 watershed load estimate)	61 years
Years needed to fill site (based on 1998 watershed load estimate, Tetra Tech, 1998)	34 years	26 years
* Crawford Multari and Star, 1993 ** Robbins and McEwen, 1999

 

Examining these data show that the current estimate for sediment loads from the watershed is more than twice the estimate used in 1993. Therefore it is not surprising that although the project's trapping efficiency is similar to initial predictions, the project is expected to collect sediment (and therefore "fill up") more than twice as rapidly as initially planned.

It is worth mentioning that any actions upstream of the Chorro Flats Enhancement Project which reduce sediment loads to the creek will also serve to enhance the longevity of this project. Specific actions could include implementation of additional best management practices for sediment control or development of additional sediment trapping areas (mini-Chorro Flats) further upstream.

Riparian Plant Community Development

The riparian plant community is developing. Willow growth exceeds expectations. Other riparian plant species are growing and will soon be large enough to persist without additional maintenance.

During October, 1997, the banks of Channels A, B, and C, and a 50 foot wide band adjacent to the banks, were planted with a mixture of native trees and shrubs . A total of 340 shrubs and 1570 trees were grown in containers and transplanted on site. An additional 8882 willow cuttings were planted (GANDA, 1998.) Plant surveys conducted in 1998 and 1999 show that these trees and shrubs are growing, and that a riparian plant community is developing. These plant surveys and associated replanting efforts are discussed below.

In July and August, of 1998 and 1999, a survey of the planted areas was conducted to:

• determine how many plants survived, and

• plan for the next season's replanting effort.

Sixty-foot wide belt transects were established perpendicular to the channels every 300 feet. Within each belt transect, all surviving trees and shrubs which were planted as part of this project were counted during each plant survey. Photographs were taken at each transect for comparison purposes.

Plant survival results for all planted tree and shrub species are summarized in Table 5.

Table 5. Plant Survival Summary

Species	1997 Planted	1998 Survival	1999 Survival
Shrubs
Twinberry	50	34%	87%
Wild Rose	75	47%	71%
Blackberry	46	2%	126%
Gooseberry	26	0%	0%
Hummingbird sage	24	0%	0%
Wax myrtle	14	63%	14%
Coffeeberry	66	53%	55%
Elderberry	39	80%	74%
Coyote bush		n/a	n/a
Total Shrubs	340	38%	74%
Non-Willow Trees
Red Osier Dogwood	211	117%	90%
Box Elder	11	0%	55%
Cottonwood	845	28%	52%
Live Oak	72	59%	53%
Sycamore	431	50%	45%
Total Non-Willow Trees	1570	63%	55%
Total shrubs and non-willow trees	1910	59%	58%
Willows
Red Willow	3231	31%
Arroyo Willow	5651	49%
Total Planted Willows	8882	42%
Volunteer Willows	0
Total all Willows	8882	256%

A Note on Willow Survival During the 1998 survey, it was noted that while the survival of planted willow cuttings was approximately 43%. However, if "volunteer" willow recruitment within the riparian band was included, the survival percentage increased to 256%. (Approximately 8,000 willows were planted in 1997, while in 1998 almost 23,000 willows were counted.) Additionally, a large and uncounted number of willow stakes were planted along the banks (as "willow mattresses", fascines, "willow baffles", and as single stakes) during 1998 and 1999. For these reasons, it was concluded that willow survival surpassed the 80% survival criteria required by the U.S. Army Corps. Therefore, willows were not counted during the 1999 plant survey.  Replanting In December, 1998, areas within the riparian zone were replanted with 1,066 shrubs and trees. Replanting efforts in 1998 were focused on cottonwood and sycamore trees, with a lesser emphasis on shrubs and other tree species. The overall survival rate of the 1998 replantings was quite low. This low survival rate may be due in part to freezing temperatures, which were encountered within days of replanting, and the generally drier conditions found in spring and summer 1999. 

Additional replantings were conducted in November 1999, and again in February 2000. During these efforts, 1,135 trees and shrubs were replanted. This replanting effort was intended to bring the number of shrubs and trees to 120% and 117%, respectively, of the numbers planted in 1997. 

Development of a Stable Stream Configuration

The stream is developing a dynamically stable configuration. First-winter changes were significant. Second-winter changes were much smaller. Future changes are expected to be small because the banks are more thickly vegetated and therefore more stable, and because the first-winter changes significantly increased the flow capacity of the channel.

During the El Niño winter of 1997-98, the entire site was repeatedly flooded, and significant amounts of sediment were deposited on the floodplain, within the old creek channel, and within a secondary overflow channel. High flows spilled into the overflow channel with such force that approximately 12,000 cubic yards of fine grained material eroded from the banks of the upstream portion of the newly installed channel. The erosion lowered the thalweg of the overflow channel so that the majority of the flow in Chorro Creek now passes through the overflow channel, with the old creek channel acting as an overflow channel. The predicted channel avulsion occurred the very first rain season following construction.

The following photos show the upstream end of the site, where significant erosion occurred during early 1998, where willow fascines were planted in 1998 to protect the bank, and where habitat improvement structures were installed in 1999.

Figure 17. Upstream end of "overflow" channel. November 1997.

Figure 18. "Overflow" channel at upstream end of project. February 1998.

Figure 19. Chorro Creek at upstream end of project. January 2000. Note habitat improvement structures and willow wattle growth.

It should be noted that a significant amount of channel realignment occurred immediately after project construction during the "El Niño" winter of 1998. We can expect that future annual changes in channel alignment will be smaller than those of 1998 because:

• these high flows occurred when the banks were relatively unprotected by vegetative growth; 
• these banks are now partially covered by riparian vegetation; and 
• the erosion of 1997-98 significantly increased channel capacity, thereby reducing shear stress on the banks.

Cross-sections of the old and new channels were measured in late 1998. These cross-sections are compared to available data regarding pre-1998 conditions, and are discussed below. Cross-sections were not re-measured in 1999 because it did not appear that significant changes in channel shape had occurred between 1998 and 1999. Cross-sectional re-measurements are planned for the year 2000, and thereafter at least once every 5 years, or every two years if a 25-year storm has occurred during that time. Cross section locations are shown in Figure 20.

Figure 20. Cross-section locations

 
Cross-sections measured in the upstream portion of the new channel show significant erosion between 1997 and 1998. In this portion of the project, the thalveg is from 4 to 2 feet lower than the bottom of the overflow channel constructed in 1997. See Figure 21. 

Figure 21. Cross-sections from the upstream portion of the project

 Cross-sections measured in the main channel in the downstream portions of the project show much less realignment than those in the upstream portion of the project. Thalveg elevations are much closer to channel bottom elevations constructed in 1997 than those found in the upstream portions of the project and the banks show very little erosion. See Figure 22.
  

Figure 22. Cross-sections from the downstream portion of the project

Cross sections measured in the old Chorro Creek channel show a mix of erosion and deposition. See Figure 23.
 
 

Figure 23. Cross-sections from the old channel of Chorro Creek

 Cross sections measured in overflow channel "B" show significant amounts of sedimentation. See Figure 24.
  

Figure 24. Cross-sections from overflow channel "B"

Changes in Bankful Flow

Channel development during the first two seasons of the project resulted in changes to channel capacity. These changes have therefore affected the flow rates that will result in overbank flow, thereby possibly changing the trapping efficiency of the project. To analyze these changes, the new channel bottom elevation profile has been compared to designed elevations and existing channel capacities have been compared to designed channel capacities. (Channel capacities were estimated using a Mannings "n" of 0.035.) These parameters are displayed in the following figures, and are discussed below.

Figure 25 clearly shows the downcutting that occurred in the upstream portion of the site. This downcutting, and associated channel widening, has resulted in increased channel capacity in this region, as can be seen in Figure 26.

Figure 25. Existing and designed channel bottom profile

Figure 26 clearly shows that the middle and more downstream portions of the site will experience more frequent flooding than the upstream third of the site. This conclusion is supported by field observations during flood events, and by topographic data. This figure also shows that the upstream portions of the site are expected to flood less frequently than initially designed. It should be noted here that the 2-year flood flow rate shown in Figure 26 refers to all of Chorro Creek at Chorro Flats, including flows in all overflow channels. Therefore, the "local" flow rates which would be expected in the new channel on a two-year return frequency are lower than the "2-year flood" value shown in Figure 26.

Figure 26. Existing and designed channel capacity
 
 

Endangered Species Habitat

Habitat suitable for endangered species is being created. Pools and riffles are developing. Steelhead and red-legged frogs have been found on the site.

A fish habitat survey was conducted in June and July, 1998, by the California Department of Fish and Game. They found 7% of the length of Chorro Creek surveyed to contain pools and 6% to contain riffles (Nelson, 1999). The remaining 87% was classified as open water. 80% of the pools were over 3 feet deep. Another fish habitat survey is planned for July 2000. We expect to see an increase in the amount of pool habitat, in part due to natural channel forming processes, and in part due to scouring associated with the instream habitat structures that were installed in 1999. For example, the largest pool on the project site formed downstream of a root-wad that was installed in 1997. A large number of fish were regularly observed within this pool during the summer of 1999.

During the fish habitat survey in 1998, CDFG personnel also sampled fish populations. They found six individual steelhead in Chorro Creek. One 5-inch steelhead was found near the center of the project and five 10-inch steelhead were found near the upstream boundary of the project (Highland, pers. comm., 2000).

In 1997 no CRLF were found on the project site during surveys conducted in July and August (Garcia and Associates, 1998.) During August, September, and October, 1999, California red-legged frogs (CRLF) were found in Chorro Creek in the upstream portion of the project as part of monitoring associated with installation of instream habitat improvement structures (Wilcox, 1999, and Morro Group, 1999.) Therefore, it appears that habitat suitable for this species is being created.

Beneficial Uses and Water Quality

Aquatic and riparian habitat beneficial uses are being enhanced. Water quality is being improved by reducing sediment loads to Morro Bay. However, riparian vegetation will not provide significant shading, and assumed improvements in temperature, for several years. The enhancement of habitat values and the reduction in sediment loads are discussed above. Water temperatures upstream and downstream of the site have been collected to document temperature changes within the project, and are discussed below. Use of the site by migratory birds has also been monitored, and is also discussed below.

The data show little difference between the periods studied. In both years, downstream maximum temperatures are generally higher than upstream maximum temperatures. This increase is generally between 3 and 5 ° F, with a maximum increase of almost 8 ° F. Larger temperature increases tended to occur when upstream temperatures were higher. This correlation is reasonable; on hotter days we expect higher temperatures at the upstream end and we also expect greater warming as the creek flows through the project.

Figure 27. 1998 maximum daily upstream and downstream temperatures

Figure 28. 1999 maximum daily upstream and downstream temperatures

Table 6. 1999 MAPS Captures at Chorro Flats