Consider Expenditure of Budgeted Funds To Conduct Survey of Carmel River Channel Profile and Cross-Sections


Meeting Date:

August 20, 2007





David A. Berger


Erosion Protection


General Manager

Line Item No.: 2-2-3




Prepared By:

Larry Hampson

Cost Estimate:



General Counsel Approval: N/A

Committee Recommendation: The Administrative Committee reviewed this item on August 9, 2007 and recommended approval.

CEQA Compliance: N/A


SUMMARY: Staff proposes to contract with Graham Matthews & Associates to conduct a survey of the long profile and selected cross-sections in the channel of the Carmel River. Approximately 15.5 miles of the river between the lagoon and the upstream end of Camp Steffani would be surveyed. The work is consistent with monitoring and technical analysis goals established for the Carmel River Management Program (CRMP), which was adopted in 1983 to restore the river channel between the Pacific Ocean and Camp Steffani. In 1993, the CRMP was subsumed into the Mitigation Program adopted in 1990 by the District for the Water Allocation Program.


Graham Matthews & Associates will set additional survey control at three locations, gather detailed ground elevation data along the profile of the channel and at selected cross-sections, conduct pebble counts, and compile data for comparison with similar information data gathered in the past (see Exhibit 3-A, Scope of Work). This data will be used to maintain a long-term record and to compare with past and future monitoring data. Comparisons of repeated surveys carried out over long periods can yield information about the long-term rate of aggradation (sediment build-up in the channel) or degradation (loss of sediment from the channel), effects of restoration projects along the river, and can inform decisions about infrastructure maintenance and repairs and proposed restoration projects. Graham Matthews and Associates has a unique set of skills and experience in gathering this type of data along the Carmel River that includes previous river surveys and other investigations as a contractor and former employee of the District.


RECOMMENDATION: Authorize the General Manager to enter into an agreement with Graham Matthews & Associates for a not-to-exceed amount of $30,000 to conduct a survey of the Carmel River channel and cross-sections.


IMPACT TO STAFF/RESOURCES: Funds for these expenditures are included in the FY 2007-2008 budget under Project Expenses for Program 2-3-3 (Survey Carmel River Profile and cross-sections, Account 4-7895.90, $30,000). Staff time will be required to administer the contract.


BACKGROUND: Most of the riverbed and streambanks along the alluvial section (the lower 15.5 miles) of the Carmel River in Monterey County, California are composed of loosely consolidated silts, sands, gravels and cobbles. Erosion along the river occurred at relatively low flows between the late 1970s and the late 1990s. The Monterey Peninsula Water Management District (MPWMD) has carried out a stream restoration program since 1983 to stabilize and restore the streamside corridor, monitor changes, provide technical assistance to riverfront property owners, and address other water-related problems along the Carmel River.


Because the river bottom changes in response to the amount of sediment that flows through it, an important aspect of managing this portion of the riparian corridor is long-term monitoring and documentation of changes in the elevation and width of the river bottom. Gravel mining, main stem reservoirs, and streambank armoring have contributed to a sediment-starved condition in the river channel downstream of Los Padres Dam, which is located at approximately River Mile (RM, measured from the ocean) 25. A chronic lack of sediment from the upper watershed has been a factor in channel incision, streambank instability, infrastructure damage, loss of property, and episodes of bank erosion downstream of Los Padres Dam over the past several decades.


One result of the sediment-starved condition of the river is that scour at the base of slope protection installed to prevent bank erosion has caused bank slumping and/or some of the bank protection works installed by property owners appear to be at risk of failure during high flows. Although MPWMD promulgated a set of standards in 1984 for installing streambank protection, it now appears that degradation (incision) in the river channel at some locations has been occurring at a rate that may induce further instability in the channel. In addition to compromising streambank stability, MPWMD staff have observed that the incision process is exposing in-channel supports (piers and abutments) at some bridge locations.


Survey data will be used by MPWMD staff and possibly other entities to review design standards, determine maintenance needs, and document the response of the channel to previous restoration projects. In addition, the design and placement in restoration projects of natural habitat features such as a pool, riffle, and glide sequence requires an understanding of these features that is gathered from repeated surveys of the river channel.


Pebble counts can be useful in monitoring changes in the grain size distribution of sediment flowing through the river. This information is used by fisheries biologists in assessing the quality of habitat for steelhead spawning, by sediment transport experts in modeling the flow of sediment, and in flood analysis simulations.


Additional background information is contained in Exhibit 3-A, Scope of Work.



3-A Scope of Work, Budget and Schedule, Long Profile and Cross-Section Survey, Carmel River Channel