At Tijuana Estuary the ocean inlet is 

 relatively shallow, so less water flows in and 

 out with the tides than would potentially fill 

 the internal channels and basins. 

 Measurements in 1987 (Williams and 

 Swanson 1987) indicated that water levels 

 rarely drop below NGVD (National Geodetic 

 Vertical Datum, or the 1929 Mean Sea Level); 

 hence, the effective tidal prism is less than 

 the potential. Williams and Swanson (1987) 

 calculated that the potential tidal prism is 

 about 0.30825 MCM (250 ac-ft). Of that 

 calculated volume, 50% is in the northern 

 arm (Oneonta Slough). 



Changes in the tidal prism were evaluated 

 by Williams and Swanson (1987). From the 

 1852 map it was calculated that the estuary 

 had a potential diurnal tidal prism of 2.018 

 MCM (1650 ac-ft) in historic times. The 

 80% loss that occurred by 1986 was 

 explained as the cumulative impact of several 

 events (Figure 2.15), most of them recent: 

 sedimentation from river inflows, sedi- 

 mentation from Goat Canyon, man-made 

 filling, landward migration of the beach, and 

 accretion along the Oneonta Slough. Mudflats 

 along the channel became vegetated with salt 

 marsh plants. 



Raw data 



, ju, „i„ _ .- , , , , a. ,*, 



l» 



V-^-\ 



40 



E 



c 



o 



20 



Log-transformed data 



i" i "| i i i i i r i " i " i ' i i" i " i n rr r i | i r rrrvf'i i | i n 

 1950 1960 1970 1980 



Years 



16 



Figure 2.14. Streamflow data for Tijuana River (Nestor gage). Log-transformed data are given to 

 emphasize low-volume flows (data from USGS 1937-1981 and IBWC 1950-1983). 



23 



