Running Water Erosion and Weathering The hydrologic cycle is a summary of the circulation of Earths water supply Processes involved in the hydrologic cycle Precipitation Evaporation Infiltration Runoff Transpiration Evapotranspiration Stream channel long, narrow depression eroded by the stream into rock or sediment Stream bank sides of channel Stream bed bottom of channel During flooding, waters overflow banks onto the flood plain of valley floor V- shaped or broad channels Factors affecting stream erosion and deposition Velocity primary influence Controlled by Gradient Channel shape Channel roughness Discharge lesser influence Velocity distance water travels in a stream per unit time Moderately fast stream 5 km per hour (3 mi/hr) Fast stream (flood) 25 km per hour (15 mi/hr) Velocity is the key to streams ability to erode, transport, and deposit sediments. Maximum velocity achieved in middle of channel Outside of curve centrifugal force faster velocities - erosion Inside of curve slower velocity - deposition Stream channel long, narrow depression eroded by the stream into rock or sediment Stream bank sides of channel Stream bed bottom of channel During flooding, waters overflow banks onto the flood plain of valley floor V- shaped or broad channels Factors affecting stream erosion and deposition Velocity primary influence Controlled by Gradient Channel shape Channel roughness Discharge lesser influence Velocity distance water travels in a stream per unit time Moderately fast stream 5 km per hour (3 mi/hr) Fast stream (flood) 25 km per hour (15 mi/hr) Velocity is the key to streams ability to erode, transport, and deposit sediments. Maximum velocity achieved in middle of channel Outside of curve centrifugal force faster velocities - erosion Inside of curve slower velocity - deposition Flood Plains Broad strip of land built up by sedimentation on either side of a stream channel Flooding covers land with water suspended with silt and clay, which gets deposited as flood waters recedes and slow down, flat smooth plain of sediment Series of floods may deposit sediment in low ridges near banks creating a natural levee Formation of natural levees by repeated flooding Alluvial fans Develop where a high-gradient stream leaves a narrow valley Slopes outward in a broad arc depositing sediment as velocity slows down Formed in dry climates where streams dont reach a body of water Deltas Forms when a stream enters an ocean or lake (mouth of stream) Shape of triangle (Greek symbol delta ) Consists of three types of beds Foreset beds- main body, angled Topset beds- next layer, horizontal fine-grained Bottomset beds in front of foreset, very fine-grained clays Stream development Downcutting process of deepening of a valley by erosion of a stream bed Limit of downcutting base level theoretical limit of erosion of earths surface V-shaped valleys Slot canyons Slow process over time Faster process mass wasting times of floods Lateral Erosion widening of channel in flood plain lateral motion Headward Erosion lengthening of channel by erosion at mouth Stream terraces step-like landforms, downcutting into new flood plains Incised meanders regional uplift of land Superposed streams erosion through the mountain range