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1.	What is a debris basin?
	A: Debris basins are facilities designed to capture sediment, gravel, boulders, and vegetative debris that are washed out of the canyons during storms but allow water to flow into the downstream storm drain system, thereby reducing flood risk for communities downstream of the facility. They are typically located at the mouths of canyons and are key components of the Los Angeles County Flood Control District's flood risk management system. In unburned watersheds, debris basins are cleaned out once they are 25 percent full. The number of years it takes to reach that level varies. In burned watersheds, where the potential for mudflows is higher, debris basins are cleaned out once they are 5 percent full. A watershed that has had more than 20 percent of its area burned within the previous 5 years is considered a burned watershed. For some debris basins in burned watersheds, this may lead to multiple cleanouts within a year.
2.	What are some of the issues of debris basins?
	A: As sediment and debris accumulate in a debris basin, the capacity to capture additional sediment inflow is reduced. If the amount of sediment and debris flowing into the debris basin is greater than the capacity available, the debris basin could overtop, allowing sediment to flow downstream and inundate downstream communities. Moving sediment out of a debris basin requires excavation equipment and numerous trucks. As most debris basins are located within residential neighborhoods to reduce flood risk for the downstream community, trucks often have to utilize local streets to transport sediment. In an emergency situation, debris basins need to be cleaned out quickly to restore capacity and be ready for the next storm. This sometimes increases operation hours as well as truck traffic.
3.	What is a reservoir?
	A: A reservoir is an artificial lake created in a river valley by the construction of a dam. The most critical purpose of reservoirs is flood risk management. Reservoirs collect water during times of high rainfall, reducing flood risk, and then release the water slowly over the following weeks and months. In addition to flood risk management, L.A. County's reservoirs assist with water conservation by providing water to the downstream spreading grounds, which are open areas where surface water can soak down into the subsurface and recharge the aquifers in a groundwater basin.
4.	What are some of the issues with reservoirs?
	A: As sediment accumulates at the face of a dam, it covers the dam's valves, making them inoperable, thereby reducing the ability to operate the dam to reduce flood risk. Additionally, as sediment accumulates behind the dam, the water conservation capacity of the reservoir behind the dam is reduced. Reservoirs are typically cleaned out as operations require and allow. Historically, it has been several years between the end of one cleanout and the start of the next cleanout.
5.	Where is the sediment and debris removed from debris basins and reservoirs taken?
	A: Much of the material is transported to regional sediment placement sites. These sites are strategically placed in close proximity to the debris basins and reservoirs to make the process of debris relocation more efficient. Some material is also taken to other sites like landfills and gravel pits.
6.	What are the issues of each sediment placement site?
	A: Sufficient vehicle access, available storage capacity, impact on residential communities, and compliance with state and federal environmental safeguards are all challenges faced by the Flood Control District in the development and operation of sediment placement sites. To prevent the sediment placement site from collapsing, the deposit of material in a sediment placement site is performed in accordance with site specific, engineered grading plans and an erosion and sediment control plan. This involves a comprehensive review of the sediment placement site, proper placement and compaction of material (often carried out in several phases), installation of temporary and permanent drainage structures, and positioning of perimeter controls. The Flood Control District's careful oversight of this process includes measures to prevent negative impacts to water quality. Depending on a site's logistical characteristics, it will be retired from Flood Control District use to become open space or recycled for future use. Recycling the site involves removing sediment for other uses, thus restoring some or all of its initial capacity.
7.	What was the impact to the District's facilities due to the Station Fire?
	A: As a result of the Station Fire of 2009 as well as the Merek, Sesnon, and Sayre Fires of 2008, the Flood Control District's management responsibilities have far exceeded previous 20-year projections of the quantity of sediment the District would have to manage to provide flood risk management and water conservation for the region. In order to address the rapidly diminishing capacity of sediment placement sites, the development of a Sediment Management Strategic Plan has been undertaken. The goal is to develop a sustainable plan for sediment management by balancing economic, environmental, and social impacts.
8.	What is the Sediment Management Strategic Plan?
	A: The Sediment Management Strategic Plan is a plan being developed by the Flood Control District to identify and address the 20-year sediment management needs. The plan is being developed with the assistance of a consultant team, a Stakeholder Task Force, and an Advisory Working Group. The draft Strategic Plan is expected to be completed by summer 2012. The Sediment Management Strategic Plan will investigate many alternatives with an emphasis on sustainable solutions. There is a constant need for sediment management and solutions will be identified to meet that ongoing need throughout the 20-year horizon at a minimum.
9.	Is the Flood Control District investigating additional sediment placement sites or alternative ways for disposing of material?
	A: During the development of the Sediment Management Strategic Plan, the Flood Control District will be evaluating a wide range of sediment management alternatives, including different transportation methods, beneficial reuse, and placement alternatives. Retired gravel pits will be considered as potential locations for new sediment placement sites. The Flood Control District will also consider developing sediment placement sites that were identified in the previous sediment management plan while investigating sustainable sediment management alternatives.
10.	Will the Flood Control District be looking at the possibility of selling the sediment to help defray the cost of sediment management?
	A: As part of the Sediment Management Strategic Plan, processing and reusing sediment will be considered. The details of the possible reuse of this sediment have not yet been explored but may include arrangements with the gravel industry, landfill operators, or other industries.
11.	How much material was removed from debris basins during the 2009/2010 storm season?
	A: The District removed close to 1.3 million cubic yards of material from its debris retention facilities. (One cubic yard is roughly the size of a typical washing machine. The Rose Bowl in Pasadena would hold about 400,000 cubic yards.) According to storm season projections, the District will need to dispose of an estimated 1.2 million cubic yards of material each storm season for the next 3-5 years, as watersheds affected by the recent wildfires recover.
12.	What steps are being taken to mitigate the impact of truck traffic on residential streets near debris basins and sediment placement sites?
	A: For routine cleanouts, the District limits the hours of its operation and extends the duration of its cleanout schedule to ease the impacts of truck traffic. The District also works closely to identify multiple haul routes, alternating the use of transit corridors to alleviate traffic impacts. During emergency cleanouts, limiting the hours of operation or lengthening the duration of the cleanouts may not be feasible if the result is not being able to ready facilities for the next storm event. Call (800) 675-HELP with comments or concerns about cleanout operations.
13.	What is the planning/permitting process for use of a sediment placement site?
	A: To begin using a sediment placement site, the District must obtain permits from federal and state regulatory agencies, which include the U.S. Army Corps of Engineers, State Regional Water Quality Control Board and State Department of Fish and Game. The District would also coordinate its effort with the local city and community members.
14.	How does the Flood Control District determine where a sediment placement site should be?
	A: The District seeks locations that have a large storage capacity for sediment placement. The District also looks for areas that are physically accessible to trucks and reasonably close to District debris retention facilities. Other desirable attributes include locations that are some distance from residences or with access points that do not travel through densely populated residential communities.
15.	Is sediment material toxic or dangerous to human health?
	A: Most of the District's debris protection facilities are located above developed areas. Consequently, the sediment retained within these structures is mostly from undeveloped watersheds that contain non-hazardous, naturally-occurring materials.

For additional questions please contact: SedimentMgmtPlan@dpw.lacounty.gov