Water San Marcos Springs

I. Water Resources and the Hydrologic Cycle

A. Two thirds of the earth is covered in water, but of that, only 3% is freshwater, and 1% is easily accessible fresh water.

B. Water is essential for biochemical reactions and is involved in nearly every environmental system – in fact, the hydrologic cycle influences all other nutrient cycles.

I’m the most important of all the biogeochemical cycles. Take that nitrogen!

I. Water Resources and the Hydrologic Cycle

C. US water use by category: 46% Industry , 41% agriculture, 13% domestic

Worldwide Water Use

70% Agriculture, 20% industry, 10% domestic

I. Water Resources and the Hydrologic Cycle

D. When precipitation occurs, several things can happen: 1) Water soaks into the soil, in a process called

infiltration

. The water may stay in the soil to be used by organisms, or percolate further down into an aquifer, and recharge the aquifer .

I. Water Resources and the Hydrologic Cycle

2) Water not absorbed into the soil flows across the land and into rivers, lakes, streams, and eventually to the oceans. Runoff waters can originate from precipitation or stem from melting snow or ice. a) An expanse of land where the surface runoff and groundwater drains into a common point – usually a stream, lake, or river – is called a

watershed

, which can range in size from a few acres to many square miles.

Major US watersheds include the Mississippi, Rio Grande, Colorado, and Colombia.

I. Water Resources and the Hydrologic Cycle

b) And, unlike water filtered by the soil, runoff water can serve as a collector of nutrients , sediment, or other pollutants on the land that can affect the quality of water throughout a watershed.

I. Water Resources and the Hydrologic Cycle

3) Most water, however, returns to the air in the form of water vapor; the bulk of this evaporation occurring by means of the oceans. Roughly half of land-based evaporation occurs on the surface area of plants, called transpiration. These together are sometimes referred to as evapotranspiration .

The hydrologic cycle

II. Understanding Aquifers

A. Aquifers provide drinking water for over half the world’s population .

B. Aquifers are in theory renewable resources, but pollution can contaminate aquifers and people frequently pull more water out than is being recharged back in.

C. Karst is a landscape formed from the dissolution of soluble rocks including limestone, dolomite and gypsum. It is characterized by sinkholes, caves, and underground drainage systems

II. Understanding Aquifers

D.

Porosity

is the percentage of open space in a rock or surface material.

Permeability

is a measure of a material's ability to transmit fluids. If the pores are very small or if they are not connected to form a channel, the material will have a low primary permeability. If the material is fractured (broken) the permeability will be increased.

II. Understanding Aquifers

E. A sandstone aquifer , for instance, acts like a sponge, and water slowly seeps between the grains of sand at a rate of inches per day. A karst aquifer, on the other hand, stores water in fractures, conduits, and cavities and can transport water up to miles per day !

II. Understanding Aquifers

F. Aquifers, to hold water, must have an impermeable bottom and top. When this happens, it is called a confined aquifer or the artesian zone. Water can escape through small holes (springs) or man-made wells.

II. Understanding Aquifers

II. Understanding Aquifers

G. Water recharges back into the aquifer in the recharge zone , an area with an unconfined upper layer, or through cracks, holes, fissures, or sink holes.

•

It’s Where We Live

These springs led to the development of major towns along the aquifer: Salado, Georgetown, Austin, San Marcos, New Braunfels, San Antonio, Uvalde, Brackettville, and Del Rio. All of these towns are sited where major springs discharge from the Edwards aquifer.

Del Rio Brackettville Uvalde Salado Georgetown Austin San Marcos San Antonio New Braunfels

III. Issues with Water

A. Main ways to get more drinking water: 1) Extract more groundwater 2) Build more dams 3) Transfer water from one place to another 4) Convert salty seawater to fresh water 5) Use water more sustainably

IV. Extract more groundwater

A. Advantages and Disadvantages

Advantages

Available year-round Exists almost everywhere Some aquifers renewable if not over pumped or contaminated No evaporation losses

Disadvantages

Aquifer depletion from over pumping Sinking of land (subsidence) Aquifers polluted for decades or centuries Saltwater intrusion into drinking water supplies in coastal areas Cheaper to extract than most surface waters

B. When water is pumped from underground aquifers, sand and rock aquifers can collapse, causing subsidence . This leads to large sinkholes. In the US, Phoenix, Baton Rouge, the San Joaquin Valley, and Houston have major problems with subsidence. Mexico City has one of the worst problems in the world, with some areas of the city subsiding as much as 33 feet.

C. Water tables are falling through many areas of the world because the rate of pumping exceeds the rate of natural recharge from precipitation.

Examples

1. India and China – Widespread drilling of inexpensive tube wells by farmers has caused the water table to drop in many area, sometimes by meters a year. The drop in the water table leads to deeper well drilling.

2. Saudi Arabia – Gets 30% of it’s water from deep fossil aquifers. Hydrologists estimate that that because of aquifer depletion, irrigated agriculture will disappear in 10 – 20 years.

3. United States – Groundwater is being withdrawn four times faster than it is recharging. The Ogallala, the world’s largest known aquifer , supplies one third of the groundwater used in the US. The Ogallala has a very slow rate of recharge (a pseudo-fossil aquifer) and is being pumped at 10 -40 times the recharge rate in TX and OK.

a. In some areas of Texas, this over pumping has lowered the water table by over 100 feet, making pumping too expensive to irrigate crops in some areas.

V. Build more dams

A. A dam is a structure built across a river to control the river’s flow. After a dam is built an artificial lake or reservoir is created behind the dam.

B. The main purpose of a dam is to capture and store run off to release or use from the reservoir as needed.

C. There are about 800,000 dams worldwide, 45,000 of them larger than 50 feet high.

V. Build more dams

Advantages

Supply reliable water Generates electricity Recreational activities Can reduce downstream flooding

Disadvantages

Can only be placed on a river Many suitable areas already dammed People displaced when built Silting occurs and renders dams useless after 50-150 years High water loss due to evaporation Species endangerment (20% world’s freshwater fish and plants endangered/extinct due to dams)

D. Examples – Colorado River Basin (US ) – 14 major dams on Colorado River. Supplies water to LA, Las Vegas, San Diego, and Imperial Valley in CA.

1. Problems: Colorado river fed by snow pack in Rockies, area in rain shadow of Rockies, legal pacts allocate more water withdrawal than river actually provides, water does not reach all the way to the Gulf of California.

VI. Transfer water from one place to another

A. Some places are water-rich and some are water-poor. Transferring water from one area to another via tunnels, aqueducts, and underground pipes can sometimes help.

B. It is relatively expensive and inefficient to transfer water.

C. Example 1: California water project 1. One of the world’s largest water transfer projects. Water is transported from northern to southern California. Causes huge conflicts in California. Agriculture uses up 75% of the water, often growing water-thirsty crops such as alfalfa and rice in desert-like conditions. Because water prices are so low, investing in improved irrigation is not economical.

2. Aral Sea disaster – In Former Soviet Union, massive water diversion project for irrigation of crops. Over 90% of original water is gone. Sea bed salts blow onto fields, polluting the soil and killing crops. Fishing industry destroyed, half the local bird and mammal species gone, loss of thermal moderation by sea.

VII. Desalination

A. Desalination involves removing salt from ocean water or brackish (slightly salty) aquifer water.

B. Distillation (boiling water and collecting the steam) or reverse osmosis (forcing water through filters with very small holes the salts can’t pass through) are the two main methods.

C. Saudi Arabia has the world’s largest number of desalination plants, and the US has the world’s second highest capacity. Israel gets 50% of it’s water from desalination and China’s costal cities get 16-25% of their water from desalination.

D. As Australia struggles with record drought, they are also building more desalination plants. They plan to get 30% of their water this way.

D. Desalination is very expensive, takes lots of energy to do, and produces large quantities of briny wastewater which is challenging to dispose of. E. Currently, desalination is practical for water short, wealthy countries .

VIII. Use water more sustainably

A. Agriculture – Many areas of the world use flood irrigation – water flowing through unlined ditches to reach crops . Over 40% of water does not reach target crops.

B. Installing an irrigation system greatly reduces water waste. Two main types:

1. Center-pivot Irrigation

- Low pressure sprinklers - Or LEPA (low-energy, precision application)

2. Microirrigation

• • Drip irrigation Trickle irrigation

C. Saving Water in City/Industry

1. Fix leaking pipe infrastructure in the city (40 60% of the water supplied to major cities in developing nations is lost through water mains, pipes, pumps leakage of

2. Homeowners

a. Change irrigation systems in lawns, switch to water-conserving landscaping – approximately 50% of water bill is lawn sprinkler systems (use TONS of water!) b. Update appliances and fixtures

D. How Can Government Help with Conservation?

1. Carrot: Provide rebates for water-conserving fixtures and appliances, rainwater harvesting barrel rebates , price breaks for using less water (currently you get price breaks for using more).

2. Sticks: Mandatory water restrictions, price increases