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Water Chemistry

 

Water - you know your life depends upon it, but how much do you really know about it? Water covers 4/5 of our planet, so it is readily available, yet water is one of the earth's most precious resources. Fresh water is precious not only because we need it to live, but also because only about 3% of all the earth's water is usable. Of the water on earth, only about one percent is available as fresh water for people to use. The majority, 97%, is salt water in the oceans; the rest is locked in the ice caps or groundwater.

Water is made from one oxygen atom bound to two hydrogen atoms. The formula for this is H2O. Water is usually found in its liquid state, but is also common in its gaseous state as vapor in the air, or as a solid (frozen). It is the only substance in nature which is commonly found in all three states. As the forms of water change, water moves from the sky to the earth and back to the sky again. This is called the water cycle. For more information on the water cycle, and other water chemistry issues, click on the links below.  

The Chemistry of Water
The Water Cycle
The Water-Soil Connection
Weather
Web links 
 

 

The Chemistry of Water 

Water is the only substance found on the earth naturally in three forms: solid, liquid and gas. The state of water is controlled by the speed of its molecules. A molecule is the smallest particle of a substance which can still retain it's physical and chemical identity. When molecules are full of energy, and moving fast and far apart, water is in its vapor state. As the molecules lose energy and cool, they slow down. Eventually, they slow down enough to cause the strong attraction between molecules to pull them together. This is when they condense, forming a familiar liquid - water. Ice is formed when the molecules lose even more energy and move very slowly.

Because of the strong attraction the molecules have for each other, it takes a great deal of energy to melt ice or make water vapor. It takes about seven times as much energy to evaporate a pound of water as it takes to melt a pound of ice. In nature, the sun provides this energy. The sun heats water and it evaporates, changing from liquid to vapor. This change takes place at any temperature between freezing and boiling. Ice can also change directly to a vapor.

The Water Cycle

The earth has had the same amount of water for millions of years. Water is used over and over by nature and is recycled in the water cycle. The water cycle is powered by the energy of the sun. The sun provides energy to first change snow and ice to liquid, then to change liquid water in the ocean, lakes, and rivers to water vapor that becomes part of the air. This is called the water cycle (click here for a diagram), which is made up of four steps which are continually repeated, with no distinct beginning or end:

1. Evaporation
2. Condensation
3. Precipitation
4. Accumulation/Percolation

Evaporation occurs when the sun's energy warms surface water on the ocean, lakes and rivers, and turns it into water vapor. Water vapor in the atmosphere collects and forms couds. This is during the condensation phase. Clouds are formed as the water vapor condenses. When the clouds are cool, water drops to the ground. This is called precipitation. Precipitation is rain, snow or hail. After precipitation, one of three things can happen to the water. Most of it soaks into the ground (percolation), and is either used by plants or becomes part of underground reservoirs called aquifers. About 1/3 of the precipitation runs off the surface and joins water in lakes and rivers (accumulation). Some of it ends up in the ocean, where the sun's energy will begin the evaporation process again. Because of the water cycle and its slow, constant recycling of water, your next drink could have once been a drink for a dinosaur! 

The Water-Soil Connection

Waters energy comes from two sources: the sun, which lifts it to high places, and gravity, which causes it to run downhill. The runoff from rain or melting snow moves huge boulders down mountains streams. By the time these rocks reach the ocean, they have ben reduced to particles of sand by the same force that took them there: water. Over time, drops of rain shape mountains. These same drops can also seep through the soil and form underground water reservoirs.

Percolation

Water stored underground is known as groundwater. Part of the water used by people in Santa Barbara County is groundwater. Water gets into the ground by percolation. It slowly seeps, or percolates, down from the surface and moves through the soil. Pore space is the space between the soil particles. Coarse soils, such as sand and gravel, have large particles and large spaces. Finer soils, such as clay, have very small particles and tiny pore spaces.

Coarse soils have much faster percolation rates because it is easier for the water to go through the larger pore spaces. The difference between water percolating through coarse and fine soil can be compared to the difference between trying to move through a room with only a few people in it and moving through a crowded room.

The Water Table

The part of the soil where all the pore spaces are full of water is called the zone of saturation. No more water can percolate in unless some is removed first. The line dividing this zone of saturation from the soil which is not full of water is called the water table. Because the amount of water in the soil changes, the water table rises and falls. Most groundwater moves slowly, usually only several inches a year. When it is moving through loose sand or gravel, groundwater can move more than 800 feet in a year. Areas where water moves down through the soil and gets into a groundwater basin are called recharge areas. Recharge areas usually have coarse soil.

One type of water table is called a perched water table. A perched water table has a layer of rock or clay under it that acts as a barrier that water cannot seep through. Below this layer, however, is often another water table. Perched water tables are frequently found on hills. Natural springs occur when part of a perched water table reaches the surface.

Aquifers

A layer of coarse soil which contains groundwater that is easily pumped out is called an aquifer. Aquifers are like sponges because they can accumulate and store large amounts of water. The groundwater we use comes from aquifers. It is pumped to the surface by wells. Wells are drilled down through the layers of soil and rock to the aquifer. Pipes are inserted into the well. These pipes have holes in the side which allow water from the aquifer to enter. This water entering the well is then pumped up to the surface.

Aquifers are filled with water by infiltration, however the water does not always seep straight down. Some aquifers have a layer of rock over them that water cannot soak through. This layer is called the aquitard. These aquifers are recharged at the point where the layer which forms the aquifer joins the surface. When this recharge area lies above the rest of the aquifer, sometimes an artesian flow can occur. In an artesian condition, water rises above the aquifer with enough pressure under the surface to force the water out naturally without pumping. Groundwater sometimes seeps up through the cracks in these areas to form springs; these springs may be hot or cold.

Erosion

When a rock is weathered it is broken up into smaller pieces. The process of weathering and moving soil and rocks is called erosion. What does water have to do with breaking up or moving soil and rocks? Water is the most powerful force in nature and is responsible for most of the erosion on earth.

There are two types of weathering: chemical and mechanical. When rocks are mechanically weathered, they are broken into smaller pieces by force, usually by the force of water. Chemical weathering is the very slow chemical change that rocks undergo, caused by chemical reactions of various minterals in and around the rocks.

Weather

Santa Barbara County occupies more than 2,700 square miles, most of which is sparsely populated and mountainous. The county is situated among a series of transverse mountain ranges, the only ranges within the continental United States to trend in an east-westerly direction. Most of the county's developed areas are located along the coastal plain and in the inter-mountain valleys. Santa Barbara County's Mediterranean climate is typically warm and dry in summer and cool and wet in winter. Most of the county's rivers, creeks and streams remain dry during the summer months. The proximity of the Pacific Ocean tends to moderate temperature near the coast while the steep mountain ranges produce a significant "orographic effect." This occurs when storms approaching the county from the Pacific Ocean are forced upward against the mountains resulting in increased precipitation release with topographic elevation. The orographic effect, in conjunction with steep, short watersheds occasionally results in flash flooding along the county's south coast.

Precipitation within the county varies greatly from season to season and with each location. Average annual precipitation ranges from a minimum of about eight inches in the Cuyama Valley to about 36 inches at the apex of the San Rafael Mountains. Snow is common at the county's highest elevations that are in excess of 6,600 feet above sea level. Climate studies have determined that drought periods occur regularly and may last as long as a decade or more. The most recent drought lasted from 1986 to 1991, during which water storage in the county's major reservoirs was nearly depleted. Only 4.49 inches of rain were recorded in downtown Santa Barbara in 1877, the driest year of record.

Although rainfall within the County is moderate on average, some winters yield well over twice the average. The maximum annual rainfall of 47.07 was recorded in downtown Santa Barbara in 1998. In addition, Santa Barbara County is occasionally subject to short duration rainfall of very high intensity (see table below). Due to it's pronounced topography and variable rainfall, Santa Barbara County has been subject to numerous periods of flooding. Significant floods were reported by Spanish Missionaries as long ago as the late 18th Century. 20th Century flood years include 1914, 1941, 1948, 1969, 1978, 1983, 1992, 1995, and 1998. For more information about flood control issues within the county, please visit the County Flood Control District's website.

El Nino 

Known to be one of the major influences on global climate, El Nino's effect in Santa Barbara County is variable. El Nino is the warming of ocean temperature in the eastern Pacific. In California, the phenomenon is often accompanied by warmer than normal air temperature and greater than normal rainfall.

The average annual rainfall in downtown Santa Barbara during El Nino years is 21.30 inches as opposed to 18.07 inches overall. However, below normal rainfall occurred during most of the El Nino years of record. In fact, fewer than half of the 27 El Nino years produced greater than average precipitation. For additional information on Santa Barbara Climatology visit the National Weather Service.
 

Web Links

USGS Water Science for Schools
Environmental Education for Kids: The Water Cycle
County of Santa Barbara Water Resources Division 



 

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