STREAMS AND RUNNING WATER Hydrologic Cycle •What happens to precipitation STREAM •River, Creek, etc. • Banks, Bed • Confined to a channel –Except in time of flood •Floodplain •Longtitudinal Profile Headwaters, mouth Cross-profile V-shaped SHEETWASH –Unchanneled, thin sheet of flowing water – Results in Sheet Erosion Drainage Basin •Tributary • Divide • Examples: –Mississippi River – Amazon River Drainage Patterns •As seen from above • Dendritic (most common) • Radial • Trellis- in tilted or folded layered rock Factors affecting stream erosion and deposition •Velocity- –Distribution in cross-section •Gradient –Usually decreases downstream – Effect on deposition and erosion •Channel shape and roughness • Discharge- –Volume of water moving past a place in time •Usually given as cubic feet per second (cfs) –Usually increases downstream •Discharge- –Volume of water moving past a place in time •Usually given as cubic feet per second (cfs) –Usually increases downstream American River Discharge •In Sacramento: • Average 3,741 c.f.s. • Usual Range: –Winter 9,000 cfs – Last drought 250 cfs •1986 flood 130,000 cfs Stream Erosion •Hydraulic action • Solution- Dissolves rock • Abrasion (by sand and gravel) –Potholes •Deepens valley by eroding river bed • Lateral erosion of banks on outside of curves Transportation of Sediment •Bed load • Suspended load • Dissolved load Deposition •Bars- –moved in floods – deposited as water slows – Placer Deposits (gold, etc.) – Braided Streams •heavy load of sand and gravel • commonly from glacier outwash streams Meandering Streams •Point bars on inside of curves • Meander cutoff –Oxbow lake •Flood Plains –Importance to farm soil – Natural levees Deltas & Alluvial Fans •Delta –standing water slows stream – Distributaries •Alluvial Fan –Decrease in gradient slows velocity of stream FLOODS •Water overtops its banks • Recurrence Interval –The 100 year flood--What it means – Sacramento Floods of 1986 •64 year flood •Flood Control –Levees – Bypasses – Dams •Problems with dams Stream Valley Development •Downcutting (abrasion of bed) • V-shaped valley- –If stream alone at work a slot canyon – Steam + Mass wasting-- V-shaped valley •Base level Graded vs. ungraded stream –-Stream attempts to establish an even grade •Through erosion and deposition –Ungraded has •Pools •Rapids • Waterfalls Lateral Erosion •Valley widens by lateral erosion –after downcutting becomes ineffective – Flood plain widens Landscape Evolution •“Youth” Initially, flat uplands dissected by streams • “Maturity” Then region in hillsides, with sharp divides • “Old Age” Hills slowly erode down as floodplains widen • Headward erosion • Stream terraces • Incised meanders.