Water

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

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.

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.

The Hydrologic Cycle

Sources of Earth’s water

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.

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.

Types of Stream Channels - Straight Straight Channel Usually occur only in short stretches Generally have a high gradient (near headwaters) Classic V-shaped valley (as opposed to glacial U-shaped valley)

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

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

Oxbow Lake 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

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

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.

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

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.

Successive drainage basins: The Yellowstone, Missouri, and Mississippi

Mississippi River Drainage Basin

Surface water resources Fresh water supply Many populations around the world lack access to clean drinking water Essential for Cause of socio-political conflicts Direct human consumption Crop and livestock Industry Scarcity of water resources

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

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

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

Groundwater Water table tends to mimic topography The water table comes up to the surface at streams, springs, and lakes

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.

Aquifers and Aquicludes 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

Types of Aquifers Unconfined aquifer Confined 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

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 H2O.