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ADMINISTRATIVE
COMMITTEE |
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4. |
Consider CONTRACT WITH WHITSON ENGINEERS TO CONDUCT
A SURVEY oF THE Carmel River CHANNEL |
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Meeting
Date: |
September 12, 2016 |
Budgeted: |
Yes |
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From: |
David J. Stoldt
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Program/ |
Erosion
Protection |
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General
Manager |
Line Item No.: 2-2-1-a |
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Prepared
By: |
Larry
Hampson |
Cost
Estimate: |
$45,000 |
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General Counsel Approval: N/A |
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Committee Recommendation: The Administrative Committee reviewed this item on September 12, 2016 and recommended _____________. |
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CEQA Compliance:
N/A |
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SUMMARY: Staff proposes to contract with Whitson Engineers for survey work along up to approximately six (6) miles of the Carmel River channel between the upstream end of the Schulte Restoration Project and downstream of Boronda Road Bridge. Detailed ground elevation data would be gathered along the profile of the channel at its lowest point (thalweg) as described in Exhibit 4-A, Scope of Work, Budget, and Schedule. 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 yields information about the long-term rate of aggradation (sediment build-up in the channel) or degradation (loss of sediment from the channel), and changes in bank storage that affect the capacity of the Carmel Valley Alluvial Aquifer to store water. The portion of the river proposed for survey work was last profiled by the District in 1984; however, FEMA conducted a less detailed survey in association with its 2009 Flood Insurance Study for Monterey County. A comprehensive survey of the lower 15.5 miles of the river will be used as part of the baseline for comparing alternatives for the long-term management of Los Padres Dam.
RECOMMENDATION: Authorize the General Manager to amend an existing agreement with Whitson Engineers for survey work to increase the not-to-exceed amount by $45,000 to conduct a survey in the Carmel River channel.
DISCUSSION: Most of the riverbed and streambanks along the lower 15.5 miles of the Carmel River in Monterey County, California are composed of loosely consolidated silts, sands, gravels and cobbles. This material makes up the water-bearing alluvium in Carmel Valley that is pumped to supply Cal-Am and non-Cal-Am demand. Because the river channel changes in response to the amount of sediment that flows through it, an important aspect of managing and understanding this portion of the riparian corridor is long-term monitoring and documentation of changes in the elevation 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 watershed area above San Clemente Dam for more than 95 years has been a factor in aquatic habitat degradation, channel incision, streambank instability, infrastructure damage, loss of property, and episodes of bank erosion along the river. In addition, incision and removal of alluvial valley deposits reduces the volume of water that can be retained in storage in the Carmel Valley Alluvial Aquifer.
Survey data will be used by MPWMD staff to adjust Carmel Valley Alluvial Aquifer parameters and to monitor effects to downstream areas from ongoing sediment retention at Los Padres Reservoir.
Whitson Engineers previously provided assistance in 2015 to survey several miles of the channel.
IMPACT TO STAFF/RESOURCES: Funds for this project are included in the FY 2016-17 budget under “Protect Environmental Quality,” line item 2-2-1-A Work at lower San Carlos Restoration Project, Account 35-03-7895.90, $50,000. Because no work is currently proposed in this Fiscal Year for this work, up to $45,000 in funds would be transferred from this item to 2-2-2 Carmel River Topographic Data. Staff time will be required to administer the contract. Additional background information is contained in Exhibit 4-A.
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