Part 3 Water beneath the surface

Chapter 6.3 : 

Chapter 6.3 Water Beneath the Surface

Groundwater : 

Groundwater Located in the pore spaces between grains of soil and sediment, and narrow joints and fractures in bedrock In USA wells and springs Provide the drinking water for more than 50% of population Are used to provide 40% of the irrigation water Are used to provide more that 25% of industry’s needs

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Some rain ends up as runoff, some evaporates, and the rest soaks into the ground The amount of water that is soaked up depends on The steepness of slopes The nature of the surface material The type and amount of vegetation

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Distribution Some of the water that soaks in stays near the surface Molecular attraction holds it in place as a surface film on soil particles This near-surface zone is called the belt of soil moisture The features in this area (plant roots, worm and animal burrows, etc) help rainwater seep into soil

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Much of the water in soil seeps downward until it reaches the zone of saturation The area where water fills all of the open spaces in sediment and rock Groundwater is the water within this zone

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Zone of Saturation The upper limit of this zone is the water table The area above the water table is not saturated and called the zone of aeration Wells cannot pump water from this zone as water clings too tightly to rocks and soil

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Movement The flow and storage of groundwater varies depending on the subsurface material The amount of groundwater than can be stored depends on porosity Porosity is the percentage of the total volume of rock or sediment that consists of pore spaces

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Rock or sediment may be very porous and still block water’s movement due to its permeability Permeability is a material’s ability to release a fluid Groundwater moves by twisting and turning through interconnected small openings. Groundwater moves more slowly when the pore spaces are smaller

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground If the pore spaces are too small, water cannot move at all Clay is a good example Has high porosity But spaces are so small that water will not move through them

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Impenetrable layers that get in the way or prevent water movement are aquitards

Distribution and Movement of Water Underground : 

Distribution and Movement of Water Underground Permeable layers of rock (such as sand) allow groundwater to flow freely These layers are called aquifers Aquifers are important because they are the source of well water

Springs : 

Springs A spring forms whenever the water table intersects the ground surface A spring is a flow of groundwater that emerges naturally at the ground surface Forms when an aquitard blocks downward movement of groundwater and forces it to move laterally Hot Springs and Geysers are examples of springs

Springs : 

Springs Hot Springs A hot spring is 43oF to 48oF warmer than the mean average annual air temperature where the spring occurs There are more than 1,000 hot springs in the USA 95% of those are in the western USA The source of heat is cooling igneous rock

Springs : 

Springs Hot Springs If groundwater circulates deep enough, then it will be heated (temp increases about 36oF for every 3300 feet of depth) When it rises to the surface, it may emerge as a hot spring

Springs : 

Springs If the hot water mixes with minerals from hot adjacent rocks, they form thick, bubbling mineral springs called “mudpots”

Springs : 

Springs Geysers A geyser is an intermittent hot spring or fountain in which a column of water shoots up with great force at various intervals Often shoot up columns of water 984 ft to 1969 ft After the water stops, a column of steam usually rushes out

Springs : 

Springs Geysers Perhaps the most famous geyser in the world is Old Faithful which erupts about once each hour

Springs : 

Springs Geysers Occur where extensive underground chambers exist within hot igneous rocks. Relatively cool water enters the chambers The surrounding rock heats the water The weight of overlying water creates great pressure that prevents the water from boiling at the normal temperature of 212oF The heat makes the water expand and forces some out at the surface Pressure reduces, boiling point drops, some of the water turns to steam, and the geyser erupts New cool water seeps back in again

Springs : 

Springs Geyser eruption cycle

Wells : 

Wells A well is a hole bored into the zone of saturation Irrigation for agriculture is the greatest use of well water in the USA Industry is the second Home use is third

Wells : 

Wells The level of the water table may change considerably during the year In the dry season it is low In the rainy season it is close to the surface To ensure a continuous water supply, the well must penetrate far below the water table

Wells : 

Wells The water table around a well drops when a lot of water is withdrawn by the well This is called drawdown and decreases with distance from the well

Wells : 

Wells The result of a drawdown is a cone of depression in the water table For small wells this is tiny, but for irrigation or industry, a very wide and steep cone of depression can result

Wells : 

Wells Artesian Well Any formation in which groundwater rises on its own under pressure Two conditions must exist to have an artesian well Water must be in an aquifer that is tilted so that one end is exposed at the surface where it can receive water There must be an aquitard above and below the aquifer to prevent water from escaping.

Wells : 

Wells Artesian Well The pressure created by the weight of the water above forces the water to rise when a well taps the aquifer

Environmental Problems and Groundwater : 

Environmental Problems and Groundwater Overuse and contamination threatens groundwater supplies in some areas Supplies of groundwater are finite In essence, groundwater is a non-renewable resource For example, in the High Plains, pumping has gone on so long, that if it were to all stop today, it would still take thousands of years for the groundwater to be replenished

Environmental Problems and Groundwater : 

Environmental Problems and Groundwater Other problems associated with over pumping The ground may sink when water is pumped faster that natural processes can replace it Part of the San Joaquin Valley (CA) has sank almost 300 feet in 50 years

Environmental Problems and Groundwater : 

Environmental Problems and Groundwater Contamination In areas where aquifers provide the water supply, pollution of groundwater is dangerous Common sources of pollution are Sewage from septic tanks Farm wastes Inadequate or broken sewers In extremely porous areas, the ground cannot filter the pollutants quickly and they will travel even farther

Environmental Problems and Groundwater : 

Environmental Problems and Groundwater How groundwater contamination can travel

Environmental Problems and Groundwater : 

Treatment Once the source of the problem is identified and eliminated, the most common practice is to abandon the water supply This allows the pollutants to flush out gradually It is the least costly and easiest solution, but the aquifer must stay unused for years To speed up the process, engineers may pump out and treat the polluted water and pump the water back in Environmental Problems and Groundwater

Caverns : 

Caverns The most spectacular results of groundwater’s ability to erode rock are limestone caverns A cavern is a naturally formed underground chamber There are thousands in the USA Most are small, but some have spectacular dimensions Carlsbad Caverns has a room that is the size of 14 football fields and is high enough to put the US Capitol building in it

Caverns : 

Caverns Erosion forms most caverns at or below the water table in the zone of saturation Acidic groundwater follows lines of weakness in the rock (joints, fractures, etc) As time passes, the dissolving process slowly creates cavities and enlarge them into caverns

Caverns : 

Caverns The feature most people think of when thinking of caverns are the depositional stone formations Form from seemingly endless dripping of water over great spans of time The calcium carbonate that is left behind produces the limestone we call travertine These cave deposits are commonly called dripstone

Caverns : 

Caverns Formation of caverns takes place while the area is in water, but formations, such as dripstone, cannot form until the area is above the water Some dripstone features are Stalactites (hang from ceiling) Stalagmites (sit on the floor) Columns (When a stalactite meets a stalagmite

Karst Topography : 

Karst Topography Many areas of the world have been shaped largely by the dissolving power of groundwater These areas are said to have Karst Topography In the USA these occur in places underlain by limestone Parts of KY, TN, AL, southern IN, and central northern FL are Karst Topography

Karst Topography : 

Karst Topography Karst Topography An area that has a land surface or topography with numerous depressions called sinkholes A sinkhole is a depression produced in a region where groundwater has removed soluble rock These depressions can range in size from just 3 feet to as much as 1640 feet (such sinkholes can swallow homes whole)

Karst Topography : 

Karst Topography Sinkholes usually form on one of two ways Downward seeping rainwater containing carbon dioxide dissolves limestone below the soil Create shallow, gently sloping depressions The roof of a cavern collapses Create deep, steep sided depressions

Karst Topography : 

Karst Topography Another identifying feature of Karst areas is the absence of streams Since the ground is so porous, rain water is quickly funneled below ground through the sinkholes where it flows through caverns until it reaches the water table If there are streams, they are usually very short

A house swallowed by a sinkhole : 

A house swallowed by a sinkhole