Fresh Water:, Lakes Groundwater & Wetlands Oct 27 Glaciers and Ice Ages Chp 13 Nov 3 Deserts and Wind and EXAM #3 Slope hydrologic cycle P = precip I = precip intercepted by veg ET = evapotranspiration Q = stream discharge R = direct runoff IF = interflow GW = groundwater triangle = water table Infiltration capacity and rainfall intensity plotted against time Infiltration capacity decreases with duration of storm Runoff occurs only when: rainfall intensity is > infiltration capacity Highly dependant on permeability and porosity of the soil and sediment Stream channel showing major water contributions Water arrival is progressively delayed from runoff to interflow to groundwater flow 1
Idealized flood hydrograph and generalized responses to drainage basin characteristics Flood hydrograph of Hurricane Agnes Flood June 1972 on the Conestoga River (Lancaster, PA) Note the curve is symmetrical - But most hydrographs show skewness with a broader recessional limb reflecting interflow and groundwater inputs The water cycle Movement of water through the 4 spheres Mostly oceans Fate of precipitation Runoff Groundwater Transpiration Water cycles moves energy Water cycle: Moves energy The water cycle Helps warm the atmosphere Absorbs heat energy Fundamental link in the biosphere 2
Flowing water in a channel River: large stream fed by tributaries Stream flow & velocity Gradient steepness Discharge volume of water flowing/unit time Channel characteristics Bank Bed Stream erosion and transport Competence how big Capacity how much Dissolved load i.e.; like salt Suspended load portion that remains suspended ( f {size and velocity} ) Bed load load that rolls, skips or bounces along the bottom 3
Downcutting and base level Downward erosion ( f {discharge, gradient, bed composition} ) Base level as far as the stream can erode Sea level is ultimate base level Bed composition, etc. can interfere Graded stream When a stream reaches a base level over the course of its gradient Sinuosity of stream channels Lateral erosion sidewards erosion Common in low-gradient streams Meander loops caused by lateral erosion Point bar depositional area, usually on inside of meander loop Oxbow lake meander that gets pinched off Braided stream network of interconnected channels Drainage basins An area of land that feeds into a river or stream Contiguous land that is all downhill Separated by mountains, ridges, or plateaus E.g.; Mississippi Embayment. 4
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Stream erosion and mountains: how landscapes evolve continuously erode towards base level along their length At the same time, tectonics tend to uplift For now, they interplay in a dynamic equilibrium 6
11.4 Stream deposition Alluvial fan deposition into dry terrain Delta deposition into aqueous environs Distributaries fan of water channels Submarine delta deposition below the waterʼs surface Floods Flood more water than a channel can hold Hazardous natural system Flood dynamics are altered by human action Flood plain low-lying land adjacent to a stream channel 7
Floods Floods & the 1993 Mississippi River Floods Artificial levees constructed embankment along stream channel Give adjacent populace a false sense of security Levees cause stream to deposit in the channel, raising the base Artificial channels dredging to straighten a river to increase gradient and velocity Scours more sediment Floods Flood plain management Choices to flood, or not to flood? Abandonment of reaches to natural forces Govʼt protection of land and landowners Patterns / regulation of development in floodplains 8
Lakes Large, inland body of standing water occupying a surface depression. Kettle lake lakes caused initially by blocks of remnant glacial ice Oxbow lake Volcanic crater lake Fault lakes 9