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Excessive rain good news for Mississippi's water supply

While the excessive rain in recent months has some people feeling down, it means good things for communities, industries and agriculture in the South. In fact, a Mississippi State University Extension Service agricultural engineer says there will never be too much rain, at least in terms of the area's underground water supply.

“Some of these aquifers were millions of years in the making,” Jim Thomas said, referring to prehistoric glaciers that melted and formed the present underground water supply. “So they will never be fully replenished, even if we stopped using them entirely.”

Aquifers are underground formations typically made of sand and gravel confined between layers of clay or solid rock that hold and store water. These geologic formations overlap each other at varying depths in Mississippi and extend for miles. Individuals and municipalities tap into these aquifers with wells to meet the population's water needs.

“Aquifers recharge through interconnection with streams and basically from deep percolation of water through the soil,” the agricultural engineer explained. “This only works on the shallow ends, and then the water flows slowly down through the material that is native to the aquifer, gradually reaching greater depths over time.”

Though groundwater reserves take longer to recharge, an advantage they have over surface water is that well water is much easier to handle and often is much cheaper to develop and treat than a surface water supply. While it seems to be more of an infinite supply, Thomas said a major limitation of surface water is its sole dependence on rainfall and run-off.

Different areas will see varying effects of the recent rainfall, depending on the depth of the aquifer used by that particular area.

“We get water from 14 aquifers in Mississippi. How much recharge you'll see depends on where you are,” Thomas said. “Those with shallow aquifers will see more of a benefit than those in areas that have deeper aquifers.”

The Mississippi Delta Alluvial Aquifer is an example of a shallow aquifer that recharges easily from the hill line of Mississippi and the Mississippi River. However, drinking water supplies for Starkville, Greenwood, Greenville and other towns that rely on deep wells do not benefit as much from recharge.

The major benefit of excessive rainfall is that the aquifers have the chance to reach adequate levels to supply water for crop irrigation without being completely depleted. In addition, the thoroughly moisturized soil will require less irrigation for crop production early in the year.

State climatologist Charles Wax, a professor in MSU's geosciences department, said areas across Mississippi received unusually high levels of rain in 2002.

“We started out above normal all over the state, then a mostly dry late spring and early summer period was followed by a wet July and a dry August/September period,” Wax said. “Beginning in September, we had big rains statewide because of the tropical storms that came across the Southern region. October was especially wet statewide last year.”

While January of this year was relatively dry, Wax said February's rainfall more than made up for any shortage the area may have felt. A household term in recent years, El Niño is a likely cause of the excessive rainfall last month.

“Typically, El Niño's effects subside in the spring, so we could see a let-up in the frequent rainfall in April or May. But it's impossible to predict what the weather will do,” Wax emphasized, referring to the “feast-or-famine” phenomenon typical of the state.

“In Mississippi, we tend to get too much or too little,” he said, “especially when it comes to rainfall.”

Keryn Page writes for MSU Ag Communications.

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