Environmental Geology Chapter 13 WATER RESOURCES

• Groundwater and Urbanization – Example • Long Island NYC/Long Island – A massive urban area with >10 million people & LOTS of pollution. There is an abundant groundwater supply and it has been overpumped and the water table has declined. Pollution has resulted from sewage - nitrates, bacteria, Industrial waste – chemicals, salts - roads; sea water, and landfills - salt, metals, nitrates • Brooklyn and Queens on western Long Island, have polluted groundwater and rely on imported water from upstate NY • Nassau and Suffolk counties (eastern Long Island) use groundwater, which is abundant, but this resource has been overpumped, resulting in dropping water table elevations, and contamination from landfills, septic tanks and salt water intrusion has degraded this resource, largely as a result of increased urbanization of the area

• Water (Hydrologic) Cycle – Evaporation-Transpiration-Precipitation- Surface Runoff/Subsurface Groundwater Flow – Powered by the Sun and Gravity

Ø Water moves vertically in the cycle through upflow: Evaporation, transpiration, and downflow: Precipitation and infiltration Ø Water moves horizontally in the cycle through surface runoff and subsurface flow

• There is plenty of Water globally, but not enough clean/fresh water everywhere people live. Abundance not a problem. Distribution in space and over time is a problem.

• Groundwater – Large drinking water resource – easily available • Groundwater = a large relative % of “available” fresh water. It is the largest easily available drinking water source. Most fresh water is tied up in ice caps and glaciers. • Although the groundwater supply is plentiful globally, it may be locally overused, causing drops in the water table. Localized shortages are result of temporal (doesn’t rain often enough) and spatial (water resources plentiful, but elsewhere) issues. • The Residence Time for water in various locations varies from days (atmosphere and streams) to many thousands of years (deep groundwater and ice caps). • Groundwater moves very slowly - typically only a few centimeters per day

• Surface Water - Drainage Basins • Drainage Basin - the total area that contributes runoff to a particular stream • Drainage divides (ridge lines, etc.) separate individual drainage basins

• Surface Runoff produces erosion of the land surface and carries sediment downstream in dissolved, suspended, and bed loads • Geological factors: Type and structure of soils and rocks (e.g. Crumbly rock, heavy weathering, and abundant fractures increase erosion potential) • Topographic factors: high relief and gradient promote erosion • Steeper slopes = faster flow = more potential erosion and sediment transport • High relief (difference in elevation between low and high areas) produces steep streams and increased erosion and sediment transport potential • Climatic factors: Type, intensity, duration, distribution of precip. • Infrequent, intense rainfall maximizes erosion via flash flooding • Vegetation factors: Type, density, size, and distribution • Vegetation can slow flow and decrease erosion and transport; removal of vegetation can increase both and drastically affect stream velocity and sediment load • Wildfires & Grazing – loss of vegetation – increases runoff • Land-use practice factors • Urbanization increases run-off, due to large amounts of impervious (blocks water infiltration) materials, such as asphalt, concrete, and building roofs • Agriculture increases runoff and sediment yield when loose, plowed sediments are exposed before crops sprout

• Groundwater Profile • Vadose zone (unsaturated zone) - below ground surface above the water table • Zone of saturation - zone below water table in which all pore space is filled/saturated with water resupplied by infiltration in recharge zones • Water table: The boundary between the above two zones

• Aquifer and Aquitard • Aquifer: A unit capable of supplying water at an economically useful rate (e.g. from a well) • Aquitard (confining layer): A layer or unit restricting and retarding GW flow

• Confined, Unconfined and Perched Aquifers

• Confined aquifer: Aquifer with an overlying aquitard layer. Artesian conditions exist when water in a confined aquifer (between aquitards) is under pressure and rises up in wells above the local level of the top of the aquifer

• Unconfined aquifer: No confining layer above it or water table as its upper surface

• Perched water table: Local water table above a regional water table (above a local aquitard-see next slide)

• Groundwater – Sinkholes. Karst landscapes involve sinkholes (roughly circular, crater-like depressions) and a rolling surface, resulting from the dissolving of subsurface limestone layers, producing caverns that periodically collapse. A wet climate is required for sufficient infiltration to cause dissolving of limestone

• Groundwater Recharge & Discharge • Recharge zone: Area where water infiltrates downward from surface to GW • Discharge zone: Area where water is removed from an aquifer, such as spring, well, river, etc. • A spring occurs when the water table intersects the ground surface

• Groundwater – Cone of Depression: The drawdown cone of GW in a well

• Groundwater – Salt Water Intrusion: coastal groundwater contamination caused by overpumping of wells.

• Desalination is the removal of salt from seawater in order to produce a fresh water resource • Very expensive and impractical in all but the most water-starved coastal areas

• Groundwater Movement – Porosity & Permeability • Porosity: Percentage of void (empty) space in sediment or rock to store water • Permeability: Measuring the interconnection of pores in a rock material. Aquifers need to be permeable to yield water.

• Groundwater Flow Rates – The Flow rate is directly proportional to the local water table gradient (or hydraulic gradient in a confined aquifer) and the ability of the sediment or rock to transmit the water (permeability/hydraulic conductivity). That is….. The greater the slope of the water table and the permeability of the aquifer the faster the water will flow through it.

• Groundwater Use and Supply • GW as primary drinking water source for ~50% of the U.S. population • GW overdraft problems (extraction rate exceeding recharging rate) in many parts of the country, particularly some states in the Great Plains region • Estimated 5% of GW depleted, but water level declined more than 15 m (20 ft) in some areas

• Groundwater levels have decreased in many areas due to overuse/pumping.

• High Plains – Great Plains (west central-southern United States from Nebraska to Texas) – Ogallala Aquifer: Since 1940 in some areas the water level has declined over 50 feet, largely due to agricultural use.

• Water Use • Offstream use: Removal or diversion from its SW or GW sources temporarily, e.g., irrigation, thermoelectric, industrial use • Consumptive use: Type of offstream use of water without immediate return, such as transpiration and human use • Aqueducts and canals are commonly used to move water from regions of abundant supply to large urbanized areas where demands exceed local supplies of clean water • Urban shortages often compounded by local groundwater contamination due to urbanization itself, requiring import of most or all of the needed supply • Instream use: Navigation, fish and wildlife, recreational uses, hydroelectric power

• Water Use in major urban areas has lead to: • Over-withdrawal of groundwater • Overuse of local surface water • Threats of local urban landfill to the water supply, e.g., Long Island, NY • Water import issues and problems: What is distance to transport? How much water available? From where? Conflicts with other areas, litigations, and long-range planning

• Trends in Water Use (Based on the data from 1950–1995) • Surface water (SW) use far greater than groundwater (GW) use • The rate of water use has slightly decreased and subsequently leveled off since 1980 -- decreases in use by thermoelectric power generation and flat demand by agriculture (due to more efficient practices) have more than offset increases in public demand resulting from population growth. New technology and recycling have contributed. • Irrigation and thermoelectric are major fresh consumptive water use

• Water conservation practices, especially regarding efficiency and/or recycling uses in agriculture and industrial/power plant needs, may yet decrease our total water usage for some time to come, in spite of population growth

• Water Conservation will depend on: • Engineering technology and structure (canals): Regulating irrigation and reducing evaporation • Better technologies in power plants and other industries: Less use of water due to improved efficiency • Increased water reuse and recycling • Energy efficient appliances

• There is a need for water management due to: • Increasing demand for water use (population and economic development) • Water supply problems in semiarid and arid regions • Water supply problems in mega cities of humid regions • Water traded as a commodity: Capital, market, and regulations?

• Water Management Strategies we can use: Ø More surface water use in wet years, more groundwater use in dry years Ø Reuse and recycle water on a regular basis as well as during emergencies

• The Colorado River is one of the most heavily managed (and spoken for!) water resources in the U.S. Management for public use, as well as for river environmental conditions in the Grand Canyon, are both involved

• Managing the river Ø Dam and aqueduct construction Ø Decreased flood frequency Ø Sediment flow interrupted Ø Impact on wildlife habitats Ø Controlled and planned floods • Lower Colorado River Allocation Ø 59% to California Ø 37% to Arizona Ø 4% to Nevada Ø All of the water is allocated in both the upper and lower Colorado River basins • Water Management & Control Structures - Water management that involves building of artificial control structures, such as dams, reservoirs, and aqueducts, has some negative environmental effects, such as: • Loss of land flooded by new reservoirs • Trapping/removal of sediment that would have traveled down the river system • Change of downstream habitat w.r.t. Lost sediment, colder water, increased scour and streambed erosion, reduction of natural variation in river flow rates, etc.

• Water and Ecosystems - General tendency: Increased human use of water, increased degradation of natural ecosystem

• Wetlands-Wetland Ecosystems are areas inundated or saturated by surface or groundwater that support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas."

• Overall reconciliation between multiple water uses Ø Dam construction impacts environment Ø Reconciling water uses: Agriculture, industry, beach and sand bar ecosystem, recreation

• Water Shortages & the Future • Groundwater depletion around the globe over the past 50 years is largely a result of the tripling in agricultural demand for irrigation of crops to feed the ever-increasing human population • Future water shortages are, then, likely to lead directly to food/crop shortages as insufficient irrigation water might be available • Conservation of water and controlling population growth are two keys to avoiding this potential food crisis

WSE 8/2012