Tides and Currents 



Tide gages deployed at the mouth of the river in May 1990 were not 

 relocated during a scheduled retrieval in December 1990, and are presimied to 

 have been buried by sediment. Additional gages were not deployed at that 

 location, because tidal fluctuation information was available from the offshore 

 wave gages. These data showed that the Colorado River area has a mainly 

 diurnal tide with a spring range of approximately 0.9 m. During neap tides a 

 semidiurnal component becomes evident. This is in agreement with other 

 published values (e.g. Aronow and Kaczorowski 1985). Tidal data are shown 

 in Figure 22. 



Currents were measured at the mouth of the river during the first surf zone 

 experiment using an upward-looking, narrow-band ADCP. A Puv gage was 

 deployed adjacent to the ADCP to measure currents in the bottom meter of the 

 water column. The data were combined and processed by Scientific Services 

 as described in Lacey (1990). 



For times of low rainfall within the Colorado River watershed, currents in 

 the Colorado River mouth are mainly tidal driven. An example is shown in 

 Figure 23 for the period May 4-7, 1990. This sample corresponds to a period 

 of neap tide range. The maximum ebb and flood currents of 2.5 to 3 m/sec 

 shown in Figure 23 are substantially greater than at most tidal inlets. Spring 

 tides produce substantially greater tidal amplitudes, but because spring tides are 

 diurnal, the currents are not correspondingly stronger. A comparison of these 

 data with published current data predictions for Galveston bay entrance 

 (U.S. Department of Commerce 1990) indicates that astronomically driven tidal 

 currents at the mouth of the Colorado River may occasionally reach up to 

 6 m/sec. However, periods of high rainfall could greatly strengthen ebb flows 

 and decrease flood currents. 



The ADCP was also used to make a qualitative assessment of the suspended 

 sediment load in the river by plotting the backscatter intensity. An example of 

 this is shown in Figure 24. However, no attempt was made to extract 

 quantitative suspended transport rates from these data. 



Mean coastal current information in water depths of about 10 m was also 

 obtained from the offshore Puv (but not DWG) wave gages. These mean 

 currents, shown in a current rose. Figure 25, are 300-sec averages of data 

 obtained hourly. Figure 25 shows the direction that the currents were coming 

 from. These coastal currents were generally parallel to shore, with a plurality 

 being from the southwest. Speeds were generally less than 0.5 m/sec. 



40 



Chapter 4 Data Observations and Analyses 



