Temperature Effects in Clear Lake and Galveston Bay
Childers, Ralph E.
Hiser, Leland L.
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The study of temperature effects in Clear Lake and Galveston Bay was initiated in 1964 when a series of temperature distribution studies were made in Clear Lake prior to the operation of the No. 3 generating unit at the Webster Station. The results of these studies were previously reported in Technical Progress Report No. 1 submitted in August of 1965. In early 1965, the No. 3 unit started operation and increased generation capacity from 220 megawatts to approximately 570 megawatts. The cooling water canal system was changed with the addition of a new four-mile discharge canal entering Clear Lake from the south. A relative evaluation of the lake performance as a source of cooling water was made in July of 1965 with generation at approximately 525 megawatts and the entire coolant flow diverted through the new discharge canal. The presence and relative abundance of the various types of plankton at selected locations on Clear Creek and Clear Lake was also determined. Temperature distribution studies were repeated in 1966 with power generation the same but the coolant flow was distributed between both discharge canals. The plankton sampling and analysis were also duplicated and a letter report was submitted on August 8, 1966. A temperature distribution study was also conducted at Bacliff, the point of discharge for the P.H. Robinson Station which at that time had a generation capacity of 450 megawatts. The temperature distribution studies at Clear Lake were not repeated in the summer of 1967. However, a study of the dissolved oxygen balance in the cooling water system was made and Technical Progress Report No. 2 entitled Oxygen Balance of the Webster Generating Station Cooling Water Canal System was submitted in November of 1967. The plankton sampling and analysis were again duplicated. Based upon the investigations conducted by Southwest Research Institute, the following conclusions and recommendations are made: (1) Under the present system configuration and generation capacity at Webster Station, it is improbable that th plant intake temperatures will be affected by short-circuiting of heated cooling water. The major influence on intake temperatures will be meteorological conditions. (2) The interrelation between the two discharges in Clear Lake under present conditions is relatively minor, and the two lobes of heated water are separated by an area of water only slightly higher than the ambient water temperature. (3) Thermal stratification in Clear Lake is insignificant except near the new canal outlet during mild wind conditions. (4) The area of water in Clear Lake which is at an elevated temperature does not vary significantly but does shift in position due to wind and tides. (5) From 15 to 25 percent of Clear Lake can be above normal lake temperatures. The normal temperatures in Clear Lake during July may be two to three degrees higher than Galveston Bay water temperatures. (6) At the new canal discharge to Clear Lake the area of heated water has been observed, under maximum values of plant loading, to reach from shore to shore with temperatures three degrees above the normal lake temperature. This condition might temporarily restrict migration routes of some marine organisms. (7) Additional expansion at Webster is not recommended under the current canal configuration. Expansion of generation capacity might be accomodated by relocation of heated water discharge points. (8) No significant differences in plankton distribution or relative numbers in Clear Lake have been observed over the 1965 to 1967 period. (9) The use of airborne temperature sensing equipment should be seriously considered for future temperature distribution studies of this type.