Friends of San Lorenzo Creek

Key Terms

Bank — the sloping area between the water’s edge and level ground. Roots and vegetation stabilize the banks, filter sediments, and reduce soil erosion.

Buffer — a vegetated area of grass, shrubs, or trees designed to capture and filter runoff from surrounding land uses.

Creek bed (or streambed) — the bottom of the creek (or any water channel), which is usually composed of a mixture of gravel, sand, and silt.

Creek channel — the area of the riparian corridor that periodically or continually contains flowing water.

Deposition — settlement of materials from moving water onto the channel bed, banks, and floodplains. Deposition occurs when flowing water is unable to transport the material.

Floodplain — any lowland that borders a stream and is inundated periodically by its waters.

Groundwater — the water contained in the open spaces between individual soil particles. Below the ground surface and above the water table, water in the soil does not fill all the open spaces. Groundwater is not the same as surface runoff.

Headwaters — uppermost reaches of a stream.

Perennial stream — a stream that flows continuously throughout the year.

Pools — deeper portions of the creek where sediments have been scoured and water flows slowly. Pools are important habitat components for trout and other native fish.

Riffles — shallower areas in the creek where water flows quickly, often over gravel or rocks.

Riparian corridor — the vegetated area adjacent to (and including) the creek.

Riprap — a layer, facing, or protective mound of rubble or stones randomly placed to prevent erosion, scour, or sloughing of a structure or bank.

Run — the straight fast-moving section of a stream between riffles.

Runoff (surface runoff) — the portion of rain that moves over the ground toward a lower elevation and does not infiltrate the soil. "Urban runoff" refers largely to water from rain, irrigation, or industrial and household discharge that typically flows into a storm drain system that empties into a body of water (locally the San Francisco Bay). Runoff is not the same as groundwater.

Scour — concentrated erosive action of flowing water in streams that carries away material from the bed and banks.

Sediment — the soil particles in the creek. The sediment can be on the bottom of the creek or it can be suspended in the water. Water with a high sediment load (or turbidity) looks muddy or cloudy.

Sloughing — downward slipping of a mass of soil, moving as a unit usually with backward motion, down a bank. Sloughing is similar to a landslide.

Upland zone — extends away from the wetter riparian corridor.

Watershed — the land area that water flows across or through on its way to a creek, river, bay, or ocean. Rain that falls in the San Lorenzo Creek Watershed makes its way to one of nine major creeks. Bolinas, Castro Valley, Chabot, Cull, Crow, Eden Canyon, Hollis Canyon, Norris, and Palomares Creeks all empty into San Lorenzo Creek.

Woody debris — includes trunks and large branches of trees that have fallen into or alongside the creek.