\ 



TRINITY RIVER DISCHARGE 



In January 1961, 12 stations were established in Trinity Bay, these 

 being located along three gridlines (four per line) oriented with the long axis 

 of the bay, which runs from the Trinity River delta to a line extending from 

 Houston Point to Smith Point. Operations at each station included a Secchi 

 disc reading for turbidity, surface and bottom measurements for temperature 

 and salinity, and a 5-minute trawl haul for biological specimens. Considerable 

 bias is created in Secchi disc readings due to variations in cloud cover, posi- 

 tion of the sun, and recording methods utilized by different individuals. Bias 

 is also possible in the trawl samples due to the alternate use of several dif- 

 ferent vessels. This sampling continued through April 1962 on a biweekly 



basis when weather permitted. 



With only two exceptions, 

 the monthly mean bottom salinity for 

 each tier of three sampling stations 

 increased with increasing distance 

 from the mouth of the Trinity River. 

 (See accompanying figure. ) The high 

 salinity recorded in September for 

 Stations 1-3 may be in part due to 

 pockets of high saline waters depos- 

 ited in upper Trinity Bay by Hurricane 

 Carla, which passed through the area 

 on September 9-12, 1961. A study of 

 river discharges into, and salinity 

 levels within, Trinity Bay indicates 

 that increased discharges of fresh 

 water are generally associated with a 

 lowering of salinity, and vice versa. 

 (See figure. ) Lags between varying 

 discharge and the associated rising or 

 lowering of salinity are commonplace 

 phenomena in the study area. 



Light penetration recordings 

 by means of Secchi discs range from a 

 minimum of 7 cm. to a maximum of 

 90 cm. The greatest turbidity was ob- 

 served in a belt from the mouth of 

 Trinity River to Smith Point, while the 

 northwest half of the bay was slightly 

 clearer. 



Water temperatures ranged 

 from 3. 5° to 29. 8° C. at the bottom, 

 whereas the surface temperatures 

 ranged from 1.0" to 29.9° C. These 



1 — I — r 



T 1 1 1 1 1 



TRINITY BAY SALINITY 



Stotions 



I - 3 = — 

 4-6 = -- 

 7-9 = ■■• 

 10-12 = -■ 



FEB M 

 1961 



n — I 



M APR 

 1962 



Monthly mean salinity for four 

 tiers of sampling stations in 

 Trinity Bay, February 1961 to 

 April 1962. 



68 



