Trees also control snowmelt by casting shade on the snowpack and reducing wind speeds at the snow surface. Trees withdraw water from the soil through transpiration. Forestry activities and stream flows The stream flow section of the CWAP focuses on two issues surrounding peak stream flows. Clearcuts and roads tend to increase peak flows, thereby increasing rates of channel change and sediment movement within the channel. The presence of hillside roads increases peak flows.
Hillside roads intersect surface and subsurface flows.
Road ditches capture and concentrate small streams and overland flow between cross drains. This tends to increase the rate of delivery of surface water to the main stream. Subsurface water is intercepted by road cutslopes and, unless this water is returned to the soil quickly, it becomes surface flow. The result is that roads convert groundwater seepage into surface stream flow, significantly increasing the rate of water movement to the main stream channel and effectively increasing the stream drainage density. Under wet conditions, a high road density can significantly increase peak flows.