Somerville Lake in south-central Texas is a shallow lake, with a mean depth of 14 feet. The maximum depth of the submerged channel of Yegua Creek is usually less than 35 feet and in most areas of the lake the depth is less than 10 feet. Several factors including thermal circulation resulting from the cooling of surface water, wind action, and the large inflow volume in realtion to the lake volume combine to keep the lake well mixed throughout the year. The oxygen concentrations remain high areally and at depth because of good circulation of lake waters during most of the year. Even in summer most bottom oxygen concentrations were in excess of 50 percent of saturation. the water ranged from 75 to 140 milligrams per liter, expressed as calcium carbonate, placing it in the moderately hard to hard (61 to 180 milligrams per liter) classification. The concentrations of principal dissolved constituents indicate that Somerville Lake is an excellent source of water for municipal, industrial, or agricultural use. I en 01 DISCHARGE, IN CUBIC METERS PER SECOND

Cumulative-frequency curve, a curve prepared for dissolved-solids concentration by arranging dissolved-solids values of individual samples in order of magnitude and dividing them according to percentages of time during which specific values are equaled or exceeded. This type of curve also referred to as a duration curve. Specific conductance of water, a measure of water's ability to conduct an electric current. Expressed as micromhos per centimeter at 25° C. Varies with concentration and degree of ionization of different minerals in solution and with temperature of water. Furnishes rough measure of dissolvedsolids content of water but does not give any indication of relative quantities of constituents in solution. Pollution, as used in this report, defines conditions in which dissolved-mineral concentration of water exceeds acceptable limits for a particular use. Artificial pollution refers to conditions which have been manmade; natural pollution refers to conditions that man did not create, such as brine inflow from natural salt deposits.

To obtain square meter (m) cubic meter (m3) cubic meter per second meter (m) kilometer (km) (rr,3 /s) National Geodetic Vertical Datum of 1929 (NGVD of 1929): A geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called "mean sea level." VI WATER QUALITY OF BELTON LAKE, CENTRAL TEXAS