The potential for water-supply development in Harrison County is almost unlimited. During an average year, more than 350 billion gallons of water flow into the Gulf of Mexico from the streams of the county. With storage reservoirs these streams have a potential sustained supply of hundreds of millions of. gallons per day. Recreation uses and flood-control benefits could also be considered in reservoir design. Upstream from the zones of salt-water penetration, mineral content is low and fairly constant. Water in the streams generally has high color and low pH ; treatment would be required for most municipal and industrial uses. Impoundment in reservoirs normally would have little effect on the quality of the surface water. However, impoundment would trap most of the suspended-sediment load of the streams. Flooding along the major streams of Harrison County is a minor hazard at present (1966), but with further industrial development and urbanization, flooding in these now rural areas could become serious. Intense rainfall from thunderstorms and hurricanes causes serious local flooding in the populous areas near the coast. Tidal flooding, a result of tropical storms, is an ever-present hazard in areas near the coast. The ground-water reservoir, which at present provides all fresh-water supplies, is capable of supporting many times the 25 million gallons per day withdrawal through existing wells. Fresh water occurs to depths as great as 2,500 feet in sand aquifers of Pliocene and Miocene age. Many of the aquifers have high transmissibility; most of those tested have transmissibility in the range, of 50,000-100,000 gallons per day per foot. Although few wells produce more than 1,000 gallons per minute, several of the aquifers can yield two to three times that amount to wells designed for the higher production. Artesian water levels along the coast are declining at a rate of 1 foot per year on the average; however, water levels are still above or only slightly below the land surface in most places, and considerable additional drawdown is economically available. Newly discovered deep aquifers (1,700-2,500 ft) have water levels 100 feet above the surface and probably will provide flow yields of 2,000 gallons per minute or more. The temperature of this deep water is nearly 100?F. Nearly all the ground water is of good quality and requires little or no treatment for most uses. It is soft, and total mineral content is usually less than 250 parts per million. Color is seldom a problem, although it may have to be considered in the undeveloped deep aquifers. The pH ordinarily is greater than 7.0, but it is slightly less than 7.0 in most places in the shallow aquifers.