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HomeMy WebLinkAboutSupplemental - Report on Beach Sand Loss and Flood Control by Charles Antos Issue Paper Beach Sand Loss and Flood Control by Charles Antos Introduction This paper identifies issues regarding the effects of regional flood control on the reduction of available beach sand and proposes a solution to beach sand loss together with an increase in flood control capacity. Flood Control (Generally) Flood control is a direct result of the need to protect urban areas from natural flooding. Drainage takes place in a basin made up of connected rivers and streams. Drainage basins almost never coincide with political boundaries and therefore flood control activities require some degree of political cooperation in order to be successful. Flood control systems consist of various artificial structures designed to contain water (rain & snow) within fixed channels and prevent the water from flooding areas outside the containment systems. The most common flood control systems consist of a series of dams and channalized rivers and streams with an open ocean outlet. Local drainage consists of systems to remove water from the land by the use of catch basins in the roads and a system of drainage channels to carry the water to the major flood control channels. Major flood control facilities have a built-in system which prevents the flow of sand to feeder beaches at the mouth of the rivers. Dams retain water/snow melt from the higher elevations until that water is released as part of the flood control (prevention) activities. By the time the water is released, most suspended solids (sands) have been deposited behind the dam. Repeated deposits reduce the capacity of the dam to hold water. If left unchecked, the dam will eventually fill up and no capacity will remain. In addition, trapping water behind a dam reduces both the volume and velocity of water in the river channels down stream. This reduces the waters ability to carry suspended solids. Sands and gravels are deposited along the river bottom, reducing the capacity of the river to carry water in times of high run off. Typically, sands and gravels are removed from the down stream river channels through long term commercial contracts with sand and gravel supply companies. These companies are only interested in the commercial value of the sand and gravel, not with the flood control capacity of the river channels. Consequently, these companies will only bid on the removal of large sand and gravel deposits. Removal of the non-commercial deposits up and down the river become the responsibility of the flood control district through their maintenance/operation/repair budget. . Issue Paper page 2 Beach Sand Loss (Generally) Sand is carried down stream by rivers and deposited on "feeder beaches" at the mouth of the rivers. These "feeder beaches" are the source of the the sand that is carried by the littoral drift from beach to beach until it is eventually deposited into off shore trenches (such as the off shore trench south of the Newport Pier) . If the "feeder beaches" stop furnishing sand for deposit down coast, the feeder beaches erode and the down coast beaches erode. Eventually the sand beaches can disappear and previously protected man made features can be destroyed by wave action. Currently, in order to preserve the sand beaches, sand is imported and placed on the "feeder beaches" . This sand comes from off shore dredging operations and/or from river bottoms. Typically, not enough sand is available for purchase, is of poor quality (grain size too small or mixed with mud) , is too expensive or must be transported very long distances. The result has been an overall loss of sand beaches, significant man made feature damage and changes in the contours off shore. In order to preserve the sand beaches (feeder beaches) , a reliable source of quality sand must be located as well as a reliable method of transporting the sand to the beach must be developed. In addition, the cost of the sand transportation must be addressed. Proposal for Sand Replenishment Construct a pipeline along the major river channels from the dams to a holding or storage area near the feeder beach. Transport the sand mixed with water (similar to slurry) by pipeline to the holding area. Separate the water from the sand and place the sand on the beach as needed. With proper permits, sand can be placed on the beach at any time of the year except during the grunion breeding season. Positive Aspects: * Sand is available as needed. * Fresh water is available for use in fresh or brackish water wetland restoration projects or to replenish ground water (thus preventing salt water intrusion in the coastal zone) . * The flood control capacity of the dam is maintained by removal of excess solids. * The California Coastal Commission would most likely support the project since it maintains and enhances sand beaches, thus preserving "public coastal dependent visitor serving uses within the coastal zone" . Issue Paper page 3 * The Army Corps of Engineers would most likely support the project since it removes them (and their budget) from annual requests for permits as well as annual requests for Federal funding for sand replenishment. * Other stakeholders would most likely support the project (ie. coastal property owners, Surfrider Foundation, fisherman, Sierra Club, Fish & Game, Fish & Wildlife, coastal cities etc.) * No right-of-way cost is involved since all facilities are owned and operated by the flood control district. Cost: The estimated cost of a pipeline (gravity & low pressure) for water/sand slurry is $1, 000, 000/mile. Sand would be removed from behind the dam by power dredging and deposited into the pipeline. (cost of power dredge and labor unknown) Possible Funding through: * Army Corps of Engineers since the pipeline would relieve the ACE of annual sand replenishment costs. * Wetland mitigation funding since fresh water needed for fresh water and brackish water wetlands is provided by pipeline (after sand is removed) . * League of California Cities and Counties sponsored new State legislation to create a Drainage Basin Maintenance Fee Program. Drainage Basin Maintenance Fee Program: This program would be based upon the concept that development (hardscape) reduces the natural absorption area on vacant property. The addition of buildings and hardscape prevents absorption and forces the flood control system to handle the increased runoff. The costs of handling this increased runoff would by collected at the time of issuance of building permits (similar to collection of Major Thoroughfare and Bridge Fee Program [Road Fee Programs] fees) . The fee would be based upon the percent of reduction of absorption on the land/lot from its vacant condition to its developed condition. The percent of absorption reduction would include: buildings as well as hardscape permitted by zoning. For example: * Commercial/Industrial Total lot - setback along the street(s) (which is required to be landscaped) [shopping center of 1 square mile with roads on 4 sides would have a maximum of a 4% landscaping requirement leaving 96% reduction in absorption] Issue Paper page 4 * Residential Total lot (100% reduction in absorption) The fee rates would have to be determined based upon the difference between: a) Total cost of new flood control facilities needed to compensate for the cumulative reduction in natural absorption caused by development. b) Total cost of maintenance dredging and sand removal to maintain the flood control system at it' s present capacity. The fees would be collected by the permitting agency (city or county) and deposited with the flood control district to be used only to maintain the existing capacity of the flood control system. Conclusion The concept of solving two problems by dealing with one (preserving the capacity of the flood control system) deserves to be studied. The proposed solution will require cooperation of the flood control districts, cities, counties and the State in order to have the necessary laws enacted.