San Lorenzo Creek Watershed
We all live in a watershed, natural drainage basins separated by barriers such as ridgetops and hills. All of the land that rainwater flows through on its way to a natural collection point, such as a creek or the Bay, is part of that watershed. A creek system is the visible, above ground portion of the drainage system.
The San Lorenzo Creek watershed is a system of many smaller watersheds that drain 50 square miles of Alameda County into the Bay. Rain that falls in the watershed makes its way to many creeks that merge and eventually join San Lorenzo Creek. The watershed begins in the East Bay hills on the western side of Dublin, runs through Castro Valley and San Lorenzo, and includes portions of San Leandro and Hayward (with its engineered drainage system that now flows into San Lorenzo Creek).
Floodplains Are Natural Creek Overflow Areas
Floodplains are land areas near creeks that, in their natural state, would be subject to flooding when creeks overflow during heavy rains. As urban development has increased, we’ve needed to build flood control infrastructure to protect against floods. Urban development results in pavement, roofs, and other hard “impervious” surfaces that don’t let water percolate down into the ground. As a result, stormwater runoff to the nearest creek increases, which would increase the chance that creeks would overflow without the flood control infrastructure that’s in place.
