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Texas Water Supply Lakes (or Reservoirs?)

Technically, the words "lake" and "reservoir" describe different types of bodies of water. The word "lake" comes from the Greek word "lakkos, meaning hole or pond. A "lake" is a naturally formed body of water surrounded by land. Most true lakes in the U.S. are in the northern part of the country and were formed by glaciers (i.e. Lake Superior, Lake Huron, Lake Michigan). Lakes can also be formed by the combination of sinkholes and springs (such as in parts of Florida), in craters of extinct volcanoes, or when the deposition of silt in a river closes the natural outlet to a sea.

On the other hand, a body of water not formed by natural means is technically a "reservoir". Colloquially in Texas, it seems common to refer to reservoirs as lakes (i.e. Lake Arlington, Lake Worth, or Possum Kingdom Lake, etc.), but technically these are reservoirs, or artificial lakes, created by manmade dams. One of the few, if not the only, truly natural lakes of any size in our state is Caddo Lake (in northeast Texas). Popular legend holds that Caddo Lake was created by after-shocks of the New Madrid, Missouri earthquake of 1811-12; however there were accounts of a swampy area in existence in 1712. Man created all other major so-called "lakes" in Texas.

As urban populations grew, the reliable, recoverable quantity of water available from rivers and groundwater became inadequate to meet domestic and irrigation water supply needs. This created a demand for civil engineers to design man-made "reservoirs" for water supply purposes. Most reservoirs are "multi-purpose", having some combination of water supply, flood control, recreation and/or wildlife-related uses. Progress in achieving these uses comes at the expense of flooding/destroying many square miles of agricultural and timber land, and destroying natural areas of diverse wildlife habitat along stretches of the state's 15 major rivers and other tributaries.

There are over 6,700 reservoirs in Texas whose surface area is 10-acres or more. But the storage capacity of Texas' 212 major reservoirs (those having a capacity of more than 5,000 acre-feet) represent over 97% of the conservation storage in all Texas lakes. In 1913, there were only eight major reservoirs in Texas. The growth in dam/reservoir building in Texas is illustrated by the following number of major reservoirs that existed in subsequent decades: 11 in 1920; 32 in 1930, 47 in 1940; 66 in 1950; 105 in 1960; 149 in 1970; 168 in 1980; 190 in 1990; 212 in 2000.

- John P. Wier, P.E., R.P.L.S., Historical Chair, Fort Worth Branch ASCE, November 2001

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