WHAT IS A WATERSHED?
The term "watershed", or drainage basin, refers to a geographic area where water and sediment drain to a common outlet. Watersheds are those land areas bounded by topographic features on the landscape (ridge lines) that catch falling rain and snow which drains to creeks, rivers, lakes, estuaries, lagoons, marshes, the ocean, or groundwater basins.
IMPORTANCE OF WATERSHED PLANNING
The quality of the natural environment is the cumulative result of activities within a drainage basin. Human disturbances in watersheds, such as residential, commercial, and industrial development and the construction of roadways alter natural drainage patterns and accelerate the rate of erosion and drainage through the watershed.
However, not all problems in a watershed are caused by human disturbances and not all disturbances are negative. For example, fire and flood can be particularly destructive to an ecosystem, though many species depend on these natural occurrences to survive. The intensity and frequency of these natural events is often accelerated when the landscape is modified by human activities.
Watersheds provide useful geographic units for managing natural resources aimed primarily at protecting aquatic ecosystems. The different types of aquatic ecosystems in any watershed are determined by physical characteristics such as variation of slope of the terrain; amount, frequency, and intensity of precipitation; soil type; and vegetation within the watershed.
Depending on the combination of these physical characteristics, significant quantities of topsoil, sediment, and other particles may be carried by streams and creeks from headwaters to other locations in the watershed and all the way to the ocean. Vegetation adjacent to creeks, rivers, streams, estuaries, and all other water bodies plays an important role in anchoring top soil, catching sediment, and filtering out pollutants. Maintaining a sufficient The Laguna Mountains greenbelt along the region's waterways, including intermittent streams, helps prevent erosion and siltation of streams and lagoons. These greenbelts also filter some of the pollutants that impact the region's surface and ground waters.
At the higher elevations, underground springs, rainfall, and melting snow feed the headwaters of streams which, in this regions in the region, flow to the Colorado River or the Pacific Ocean. The freshwater flow from these sources is inextricably linked to health of aquatic and terrestrial resources in each watershed. San Diego region.
WATERSHEDS IN THE SAN DIEGO REGION
The Laguna Mountains divide two hydrologic regions in the San Diego region. The San Diego Hydrologic Region (SDHR) drains in a westerly direction toward the Pacific Ocean and the Colorado Hydrologic Region (CHR) drains in an easterly direction toward the Colorado River. The hydrologic regions are composed of smaller watersheds, each defined by the natural terrain.
As shown in Map 1 on the following page, the watershed boundaries do not correspond to city limits, county boundaries, state lines, or international borders. Though some watersheds are fully contained within the San Diego region, others extend into Mexico to the south; Orange, Riverside, and San Bernardino Counties to the north; and Imperial County to the east.
