Water 2012 Pearson Education Inc Hydrologic Cycle The

Water © 2012 Pearson Education, Inc.

Hydrologic Cycle • The hydrologic cycle is a model that describes the movement of water through the reservoirs of the Earth • Processes involved in the hydrologic cycle • Precipitation • Evaporation • Infiltration • Runoff • Transpiration © 2012 Pearson Education, Inc.

Hydrologic Cycle Evaporation: 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. © 2012 Pearson Education, Inc.

Hydrologic Cycle Surface Runoff: precipitation that drains over the land or in streams Infiltration: Water works its way into the ground through small openings in the soil. © 2012 Pearson Education, Inc.

The Hydrologic Cycle © 2012 Pearson Education, Inc.

Sources of Earth’s water © 2012 Pearson Education, Inc.

Streamflow • Surface Runoff begins as overland or sheet flow as precipitation moves downhill • Sheet flow eventually becomes a stream water that flows downslope along a clearly -defined natural pathway. © 2012 Pearson Education, Inc.

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: ft 3/sec). • Stream load – suspended and dissolved sediment carried by the stream. © 2012 Pearson Education, Inc.

Types of Stream Channels - Straight Channel – Usually occur only in short stretches – Generally have a high gradient (near headwaters) – Classic Vshaped valley (as opposed to glacial U-shaped valley) © 2012 Pearson Education, Inc.

Types of Stream Channels- Braided Channel – Low gradient – Large, variable sediment load that varies seasonally (e. g. snowmelt, storm activity) © 2012 Pearson Education, Inc.

Types of Stream Channels- Meandering Channel – Usually occur downstream, near the mouth – Low gradient – Cut bank erosion and point bar deposition – May eventually form an oxbow lake © 2012 Pearson Education, Inc.

– Form when the meanders get too close together. – River cuts a new, direct channel between the meanders. Meandering Channel – Oxbow lake will eventually become a swamp and dry up. Oxbow Lake © 2012 Pearson Education, Inc.

Stream Deposits Floodplain – Flat valley floor adjacent to the stream, which is inundated when the stream overflows its banks Alluvium – unconsolidated sediment deposited by the stream © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Stream Deposits – Delta • Similar to an alluvial fan, but found at the mouth of the stream • Fan-shaped deposit as stream flows into ocean and slows down, dropping its sediment load. • Distinctive fan-shape looks like the Greek letter delta: Δ © 2012 Pearson Education, Inc.

Drainage Basins • Drainage 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 area • A drainage basin of one stream is separated from the drainage basin of another by an imaginary line called a divide. © 2012 Pearson Education, Inc.

Successive drainage basins: The Yellowstone, Missouri, and Mississippi © 2012 Pearson Education, Inc.

Mississippi River Drainage Basin © 2012 Pearson Education, Inc.

Surface water resources • Fresh water supply – Essential for • Direct human consumption • Crop and livestock • Industry • Many populations around the world lack access to clean drinking water • Cause of socio-political conflicts – Scarcity of water resources © 2012 Pearson Education, Inc.

Water-related conflicts in California • Colorado River Compact among 7 states • Dispute between Imperial County and San Diego. • Effect of Los Angeles Aqueduct on Mono Lake, Owens River Gorge © 2012 Pearson Education, Inc.

Groundwater - Subsurface water contained in pore spaces in sediment and rock • Zone of aeration (vadose zone): pore space mainly filled with air • Saturated zone (phreatic zone): pore space filled with water • Water Table: Top surface of the saturated zone © 2012 Pearson Education, Inc.

Groundwater • Groundwater moves through the interconnected pore spaces of rock and sediment from areas of higher pressure to areas of lower pressure • Rock porosity – Relative amount of space in underground rock • Rock permeability – Ease of flow through rock © 2012 Pearson Education, Inc.

Groundwater • Water table tends to mimic topography • The water table comes up to the surface at streams, springs, and lakes © 2012 Pearson Education, Inc.

Discharge and Recharge • Water percolation - Process of water seepage through rocks and sediment • Recharge - Replenishment of groundwater • Discharge – process of water moving from the subsurface to the surface. © 2012 Pearson Education, Inc.

Aquifers and Aquicludes • Aquifer – Saturated rock or sediment that is porous and permeable, so able to be accessed by well. • Aquiclude – Layer of impermeable rock or sediment from which water cannot be drawn © 2012 Pearson Education, Inc.

Types of Aquifers • Unconfined aquifer – Water table not protected from surface recharge – Vulnerable to surface and near surface contamination – Well water rises to water table and must be pumped to surface • Confined aquifer – Protected from surface by aquiclude, – Recharge area is often distant – Water under pressure and rises above water table in well © 2012 Pearson Education, Inc.

Artesian Well – Well which accesses water from a confined aquifer – Water rises in artesian wells without pumps due to release of confining pressure – Less likely to be contaminated by surface runoff, but otherwise the same H 2 O. © 2012 Pearson Education, Inc.