watershed to another to supplement 

 irrigation supplies, as periodically 

 proposed in the various versions of 

 a Texas water plan. 



In this summary we use median 

 annual freshwater flows gauged, un- 

 gauged, and return flows from 1941 

 to 1976 calculated by the Texas De- 

 partment of Water Resources (1979a, 

 b,c,d,e) divided by the total 

 volume of each estuarine system be- 

 low mean low water (Diener 1975), 

 as a rough index for comparing and 

 contrasting these estuaries with re- 

 spect to their freshwater inflows. 

 Flow medians (rather than means) were 

 used because they appear to more ad- 

 equately depict central tendencies. 

 Our discussion starts with the Sa- 

 bine-Neches system at the humid 

 Texas-Louisiana border and ends with 

 the Laguna Madre system at the semi- 

 arid Texas-Mexico border. 



Sabine-Neches 



The Sabine-Neches estuary is 

 small, comprising only 4 percent 

 of Texas' estuarine area (at mean 

 low water) , but has large fresh- 

 water inflows. This estuary pri- 

 marily supports five major fish and 

 shellfish species: bay anchovy, 

 gulf menhaden, Atlantic croaker, 

 spot, and blue crab (White and Per- 

 ret 1974; Wiersema and Mitchell 

 1973). Until the mid 1960's the 

 Sabine-Neches estuary was a major 

 white shrimp nursery and fishery 

 area, with higher catches per unit 

 area than any other Texas estuary. 

 Since 1966, the shrimp fishery has 



become virtually non-existent while 

 the blue crab fishery has increased 

 (National Marine Fisheries Service 

 1962-1977a). This estuary now leads 

 all others in Texas in blue crab 

 catch per unit area. 



Dams, which have decreased 

 spring flows and increased summer 

 flows from the Sabine and Neches Riv- 

 ers, are the cause of the loss of 

 harvestable shrimp stocks in Sabine 

 Lake (White and Perret 1974). Due 

 to higher summer demands for hydro- 

 electric power for air conditioning, 

 the operating schedule of the Toledo 

 Bend Dam on the Sabine causes high 

 winter river flows not used for irri- 

 gation to be impounded until mid-May, 

 when release begins. As a result, 

 near-freshwater conditions now exist 

 from late May through the summer. 

 Under natural conditions, discharge 

 rates into Sabine Lake were high in 

 the spring but decreased during the 

 summer, causing salinities to in- 

 crease during this time. The low 

 summer salinities caused by the dam's 

 operating schedule are not suitable 

 for brown and white shrimp (White and 

 Perret 1974). On the other hand, 

 these very low salinity conditions 

 apppear to be ideal for blue crabs 

 (More 1969). We estimate that the 

 ratio of median freshwater inflow 

 to estuarine volume in this estuarine 

 system is approximately 50. The 

 Texas Water Resources Department 

 (1979a) was not able to calculate the 

 rate of freshwater inflow required 

 for maintenance of current fishery 

 harvests . 



Trinity-San Jacinto (Galveston) 



Preliminary Texas Department of 

 Water Resources calculations for 

 the Laguna Madre were provided in a 

 personal communication from Gary 

 Powell of the Texas Department of 

 Water Resources. 



The Trinity-San Jacinto (Galves- 

 ton) estuary has just over one-fourth 

 of the total estuarine area in Texas 

 and a total median annual freshwater 

 inflow of 5.0 times the estuarine 

 volume. It leads the other Texas 



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