Transcript Chapter 20
Unit 10 - Water Part I: Water Supply, Use and Management An Arizona Watershed So what is a watershed? Watershed (review) • An area of land that drains into a lake or a river. • It is a basin-like landform defined by highpoints and ridgelines that descend into lower elevations and stream valleys. • A watershed carries water "shed" from the land after rain falls and snow melts. Drop by drop, water is channeled into soils, groundwaters, creeks, and streams, making its way to larger rivers and eventually the sea. • Remember: Water is a universal solvent, affected by all that it comes in contact with: the land it traverses, and the soils through which it travels. • The most important thing about watersheds is: what we do on the land affects water quality for all communities living downstream. http://techalive.mtu.edu/meec/module01/whatiswatershed.htm http://watershedmg.org/content/view/20/33/ The Hydrologic Cycle On a separate sheet of paper please draw out the steps of the hydrologic cycle. The Hydrologic Cycle Water Locations • Where is water located? – Oceans: 97% – Ice caps & glaciers: 2% • 99% of our water is NOT useable! – We are all competing for 1% – Atmosphere: .001% (residence time 9 days) • This small amount is responsible for producing all of our freshwater resources through precipitation. Groundwater and Streams Groundwater – – Water found below the Earth’s surface, within the zone of saturation, below the water table Define the following (page 436) in your own words: water table, recharge zones, discharge zones, vadose zone, aquifer, cone of depression Two Types of Streams: 1. Effluent Stream – – A type of stream where flow is maintained during the dry season by groundwater seepage into the channel. A stream the flows all year round is______________. 2. Influent Stream – – A type of stream that is everywhere above the groundwater table and flows in direct response to precipitation A stream the does not flow all year round______________. Interaction between Surface Water and Groundwater • If the groundwater is lowered what effects might that have on effluent streams? • What might cause reduction in groundwater? Water Supply: A U.S. Example • Water budget – a model that balances the inputs, outputs and storage of water in a system. – Defines the natural variability and availability of water • Over 99% of the Earth’s water is unavailable or unsuitable for beneficial human use • It is expected that the total water withdrawn from streams and groundwater in the U.S will decrease but the consumptive use will increase Water Use • Off-stream use: – water removed from it’s source for use • In-stream use: – the use of rivers for navigation, hydroelectric power generation, fish and wildlife habitats and recreation Water Conservation - the careful use and protection of water resources - Agricultural Use Domestic Use Industry and Manufacturing Use Perception and Water Use Possible Future Improvements Sustainable Water Use • The use of water resources by people in a way that allows society to develop and flourish into an indefinite future without degrading the various components of the hydrologic cycle or the ecological systems that depend on it Wetlands • Areas that are inundated by water or where the land is saturated to a depth of a few centimeters for at least a few days per year • Wetlands serve a variety of functions that benefit ecosystems and people Channelization and the Environment • Channelization: – An engineering technique that consists of straightening, deepening, widening, clearing, or lining existing stream channels – Purpose: • Control floods, improve drainage, etc. Channelization Summary • Humans often decide that a stream should flow along a specified path for such reasons as flood control, enhancement of drainage, control of erosion, increasing access to the floodplain for development, or improvement of the appearance of the channel. Such channel modifications involve measures such as the straightening the channel, deepening or widening the channel, clearing vegetation from the banks, or lining the channel with concrete. These modifications are referred to as channelization. Benefits of Channelization • In order to control floods, channel modification should involve increasing the channel crosssectional area, so that higher discharge will not increase the stage of the river. Straighter channels also allow higher velocity flow and, enable the stream to drain faster when discharge increases. Lining the channel with concrete provides a smoother surface over which the water can flow, thereby reducing friction and also increasing the velocity of the stream. They also allow development of floodplains. Problems with Channelization • While channelization for flood control may reduce the incidence of flooding in the channelized area, it often results in more severe flooding both upstream and downstream from the channelized area. • Channelization can also interfere with the natural habitat of the stream system and decrease the aesthetic value of the stream. • Channelized steams often have poor in-stream habitat for aquatic organisms, they can be a barrier to fish migrations and in areas where the riparian buffer has been removed, the water in the stream can be heated by the sun during the day reducing its oxygen holding capacity and raising water temperatures above the tolerance limits of some fish species. In addition, while channelization may be able to reduce flooding in one specific stream reach, often it increases flooding downstream. Flooding • The most universal natural hazard in the world • The frequency and severity are increased by urbanization • Avoid building on floodplains Desalination as a Water Source • Desalination: a technology to remove salt from water • Increased cost • Yuma desalinization plant – A desalinization plant, one of the largest in the world, built to take salt out of the Colorado River before it trickles into Mexico. The plant, constructed by the Federal government for $256 million, was promised to Mexico because the river is so salty by the time it crosses the border that Mexican farmers find it dangerous to use on their crops. This was due to salt contamination from throughout the lower Colorado region desert agriculture, but primarily from the intensive agriculture in the arid Welton Mohawk district, east of Yuma, which flushes the salt--the residue from evaporation--out of its fields, directly into the Colorado. – The plant, conceived of in the late 1970's, and finished in 1992, operated for only eight months, before laying idle again, due to a number of factors, including flood damage on some of the region's drainage ditches, wet weather naturally diluting the salty water, and the $30 million annual expense of operating the plant.