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Orange County Coastal Regional Sediment Management Plan
originated. As the upland areas erode through natural and anthropogenic processes, a broad
array of sediment is carried downstream through rivers, streams, creeks and flood control
channels. Historically, the sediment load from these upland sources provided the majority of
beach sediments (Griggs and Savoy, 1985; Richmond et. al., 2007). These upland sources
have diminished as urban development hardens landscapes, and dams, reservoirs and debris
basins trap sediment that was historically bound for the coast.
A watershed is an area of land that drains all the streams and rainfall to a common outlet such
as the outflow of a reservoir, mouth of a bay, or any point along a stream channel (USGS,
2011). The term watershed is sometimes used interchangeably with drainage basin or
catchment. A watershed includes both the streams and rivers that convey the water as well as
the land surfaces from which water drains into those channels, and is separated from adjacent
watersheds by a drainage divide. The watershed concept is so pervasive that government
agencies have been developed to solve water related issues that are best addressed on a
watershed basis. Watersheds within Orange County are shown in Figure 2.3 (County of
Orange, 2008).
While sediments travel in watersheds, they are not typically the focus of watershed concerns
and once sediments reach the coast they leave the watershed and enter what are known as
littoral cells (see Chapter 2.3). Alternately, the term sedimentshed (Martin, 2005) focuses on
sediment issues as the term watershed focuses on water issues. A sedimentshed is the area
over which the lifecycle of sediment transport occurs, encompassing upland watersheds and
coastal deposition areas in or outside the littoral zone. The sedimentshed concept would seem
a logical approach for planning and regulating RSM issues. In the remainder of this report,
watershed describes upland regions that drain into the littoral regions and sedimentshed is used
where both regions are combined.
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