Surface Water Chapter 9

Water Cycle Also the hydrologic cycle Driving force is the sun Review: condensation, precipitation, transpiration, evaporation, infiltration Runoff

Runoff Water flowing downslope along Earth’s surface –Due to gravity Can reach a body of water, evaporate, or infiltrate the ground –The path the water takes depends on Soil composition Rate of precipitation Vegetation Slope

Streams If water does not infiltrate the ground or evaporate, it eventually collects and forms stream systems –All streams flow downslope to lower elevations Tributaries are rivers that flow into other streams

Stream systems Watershed – all the land area whose water drains into a stream system –Can be large or small Divide – high land area that separates watersheds –Water flows away from the divide

Stream Load Material that a stream carries Carried in three ways –Suspension: all particles small enough to be held up by the turbulence of the water Faster water carries larger particles –Bed load: the sand, pebbles and cobbles that the stream’s water can roll or push along the bed of the stream Can cause erosion –Solution: materials can be dissolved in a stream’s water

Stream Carrying Capacity The ability of a stream to transport material Depends on –Velocity Shape of channel, amount of friction –Amount of water Discharge – volume of water that passes a point in a given time period

Floods Occur when water spills over the sides of a stream’s banks Floodplain – flat area outside of stream banks covered by excess water Natural levees – continuous ridges formed from sediment deposited over time by floods

Flood Stages Crest – highest point the water level reaches in a stream Flood stage – when the water level in the stream is higher than its banks Upstream flood – small area Downstream flood – large region –Can cause extensive damage

Monitoring and Warning National Weather Service FEMA US Geological Survey

Stream Development Stream formation relies on adequate water supply Stream channels –Headwaters: region where water first accumulates to supply a stream Common to be in mountains –Stream Channel: a narrow pathway carved into sediment or rock by moving water Stream banks: where the moving water is held

Stream Channels Headward Erosion Stream Capture

Formation of Stream Valleys Gravity and stream gradient –Movement of water down a slope –Base level: elevation at which it enters another stream or body of water Lowest = sea level V-shaped channel –Far from base, steep sides (canyons/gorges) –Downward erosion, narrow Closer to base, broader valleys with gentle slopes, side erosion

Parts of streams Meander - A bend or curve in a stream channel caused by moving water Water has the greatest velocity –In the center of the straight part of a stream –Along the outside of a meander curve Oxbow lakes – a blocked-off meander that eventually dries up Mouth – area of the stream that leads to the ocean or other large body of water

Sediment Deposition of sediment occurs when streams lose velocity Alluvial fan – when a stream drops it’s sediment at the base of a mountain in the shape of a fan (sand and gravel) Delta – triangular deposit that forms where a stream enters a large body of water (layers of clay and silt)

Rejuvenation ‘to make young again’ Downcutting – wearing away of a stream bed Rejuvenation occurs when a stream actively resumes the process of downcutting toward its base –Causes deep-sided canyons –Ex Grand Canyon

Lakes Bodies of water surrounded by land Origins –Oxbow –Streams blocked by sediment –Glacial morraine-dammed cirque –Kettle

Lakes and changes Most lakes are ‘temporary’ water-holding areas Eutrophication – when the watershed enriches bodies of water with nutrients –Stimulates plant growth –Changes animal and plant communities algae

Wetlands Land that is covered with water for part of the year –Bogs: receive water from precipitation Peat moss – acid soil (Venus fly-trap) –Marshes: form along stream mouths and deltas Lush marsh grass – reeds, rushes, wildlife –Swamps: low-lying areas near streams Support shrubs and trees (shade) Coal reserves

Importance of wetlands Water quality –Filter pollutants, sediment, bacteria Vital habitat for wildlife Wetlands used to be filled to build on Now, they are being preserved