2 Hydrologic CycleThe hydrologic cycle is a model that describes the movement of water through the reservoirs of the EarthProcesses involved in the hydrologic cyclePrecipitationEvaporationInfiltrationRunoffTranspiration
3 Hydrologic CycleEvaporation: Water changes from liquid to vapor Transpiration: Water taken up by plants passes into the atmosphere Condensation: Water changes from vapor to liquid Precipitation: Water returns to the surface of the earth as rain or snow.
4 Hydrologic CycleSurface Runoff: precipitation that drains over the land or in streams Infiltration: Water works its way into the ground through small openings in the soil.
7 StreamflowSurface Runoff begins as overland or sheet flow as precipitation moves downhillSheet flow eventually becomes a stream - water that flows downslope along a clearly-defined natural pathway.
8 Streamflow Characteristics Stream gradient - steepness of the slope. The gradient is highest near the stream’s headwaters (source) and decreases as it moves downslope toward the ocean.Stream discharge - the amount of water passing any point during a unit of time (example: ft3/sec).Stream load – suspended and dissolved sediment carried by the stream.
9 Types of Stream Channels - Straight Straight ChannelUsually occur only in short stretchesGenerally have a high gradient (near headwaters)Classic V-shaped valley (as opposed to glacial U-shaped valley)
10 Types of Stream Channels- Braided Braided ChannelLow gradientLarge, variable sediment load that varies seasonally (e.g. snowmelt, storm activity)
11 Types of Stream Channels- Meandering Meandering ChannelUsually occur downstream, near the mouthLow gradientCut bank erosion and point bar depositionMay eventually form an oxbow lake
12 Oxbow Lake Form when the meanders get too close together. River cuts a new, direct channel between the meanders. Meandering ChannelOxbow lake will eventually become a swamp and dry up.Oxbow Lake
13 Stream DepositsFloodplain – Flat valley floor adjacent to the stream, which is inundated when the stream overflows its banks Alluvium – unconsolidated sediment deposited by the stream
14 Stream Deposits – Alluvial Fans Rapid change from high gradient to low gradient environment causes stream to slow down and drop its sediment load.Fan-shaped deposit as water escapes its channel.Often found in arid to semiarid environments with infrequent rainfall/flash flood conditions.
15 Stream Deposits – Delta Similar to an alluvial fan, but found at the mouth of the streamFan-shaped deposit as stream flows into ocean and slows down, dropping its sediment load.Distinctive fan-shape looks like the Greek letter delta: Δ
16 Drainage BasinsDrainage Basin: The total land area that contributes water to a stream. Also called a watershed, or catchment basin.The drainage pattern consists of the interconnected network of streams in an areaA drainage basin of one stream is separated from the drainage basin of another by an imaginary line called a divide.
17 Successive drainage basins: The Yellowstone, Missouri, and Mississippi
19 Surface water resources Fresh water supplyMany populations around the world lack access to clean drinking waterEssential forCause of socio-political conflictsDirect human consumptionCrop and livestockIndustryScarcity of water resources
20 Water-related conflicts in California Colorado RiverColorado River Compact among 7 statesDispute between Imperial County and San Diego.Effect of Los Angeles Aqueduct on Mono Lake, Owens Lake, Owens River Gorge
21 Groundwater - Subsurface water contained in pore spaces in sediment and rock Zone of aeration (vadose zone): pore space mainly filled with airSaturated zone (phreatic zone): pore space filled with waterWater Table: Top surface of the saturated zone
22 GroundwaterGroundwater moves through the interconnected pore spaces of rock and sediment from areas of higher pressure to areas of lower pressureRock porosityRelative amount of space in underground rockRock permeabilityEase of flow through rock
23 Groundwater Water table tends to mimic topography The water table comes up to the surface at streams, springs, and lakes
24 Discharge and Recharge Water percolation - Process of water seepage through rocks and sedimentRecharge - Replenishment of groundwaterDischarge – process of water moving from the subsurface to the surface.
25 Aquifers and Aquicludes Saturated rock or sediment that is porous and permeable, so able to be accessed by well.AquicludeLayer of impermeable rock or sediment from which water cannot be drawn
26 Types of Aquifers Unconfined aquifer Confined aquifer Water table not protected from surface rechargeVulnerable to surface and near surface contaminationWell water rises to water table and must be pumped to surfaceConfined aquiferProtected from surface by aquiclude,Recharge area is often distantWater under pressure and rises above water table in well
27 Artesian Well Well which accesses water from a confined aquifer Water rises in artesian wells without pumps due to release of confining pressureLess likely to be contaminated by surface runoff, but otherwise the same H2O.