relatively dense south of the apartments. 

 Near the mouth were disturbed areas and 

 areas of bare sand toward the main estuary 

 channel. A second dike had been built within 

 the inland lagoon. Sewage was then discharged 

 to two oxidation ponds before overflowing to 

 the estuary. The nearby bridge remained, and 

 extensive disturbance by vehicle traffic had 

 occurred. 



By 1970 several new disturbances were 

 visible. Additional apartments had been built 

 along the coast, and the barrier dune no longer 

 supported good vegetative cover. Large areas 

 of dune washover had developed both north and 

 south of the estuary mouth. As is obvious 

 from events of the 1980's, this relatively 

 gradual loss of dune vegetation ultimately had 

 an estuary-wide impact. The sewage 

 operation at the inland lagoons had been 

 abandoned, and saline pannes were obvious 

 during the July, dry-season photo. Tidal 

 flushing was lacking behind the diked areas. 

 The mouth had shifted southward. East of the 

 sewage impoundments, a channel had been dug 

 to direct street runoff into the southernmost 

 lagoon. 



The year 1983 was one of the strongest El 

 Nifio events on record (R. Flick, Scripps Inst, 

 of Oceanography, pers. comm.). Associated 

 with the warmer sea temperatures were 

 higher sea levels (15 cm above average) and 

 frequent storms. The storm activities were 

 evident at the estuary. 



In January 1983, concurrent high tides 

 and heavy surf flooded Sea Coast Drive and 

 washed sand between the apartment buildings 

 into the street and onto the edge of the salt 

 marsh. Where dune vegetation had been 

 disturbed, there were major washovers. The 

 photo from March 1984 (Figure 2.9) 

 documents the effects of the winter storms on 

 the barrier beach, while that of August 1984 

 (Figure 2.10) shows the delayed effect on the 

 estuary mouth. Dune sands were washed into 

 the main estuary channel, substantially 

 reducing the tidal prism and ultimately 

 causing the closure of Tijuana Estuary to tidal 

 flushing. Closure occurred on or about April 

 8, 1984, after which a dredging plan was 

 developed and implemented by the U.S. Fish 

 and Wildlife Service. Excavation of the sand 



from the main channel began after a long 

 permit process, but the estuary was not 

 reopened to tidal flushing until mid-December 

 1984. Eight months of closure had 

 devastating effects on the estuary. 



While the reduction of tidal flushing is in 

 itself a catastrophic event for a marine- 

 dominated system, the situation was made 

 worse by its coincidence with a year of near- 

 zero rainfall. Channels became hypersaline 

 (60 ppt in fall 1984; R. Rudnicki, SDSU, 

 pers. comm.), shallow creek bottoms 

 desiccated and turned to brick, and marsh 

 soils became so dry and hypersaline (over 

 100 ppt in September 1984) that large areas 

 of low-marsh vegetation died out (Figure 

 2.11). Bare patches within the salt marsh 

 were obvious from the air in August 1984 

 (Figure 2.10). 



Tidal flushing was reinstated in December 



1984 after dredging of the main estuary 

 channel from the end of Sea Coast Drive south 

 to the mouth, and tidal flushing has continued 

 to the present. Sand that washed eastward was 

 bulldozed back to recreate dunes, which are 

 now part of a dune revegetation program. 

 Additional dredging in the south arm of the 

 estuary was done in 1986, along with dune 

 rebuilding activities. 



In comparison with earlier estuary 

 conditions, several changes had occurred by 



1985 (Figure 2.12). Native dune vegetation 

 was almost entirely gone both north and south 

 of the mouth. Along the channels, salt marsh 

 vegetation that died back in 1984 had begun to 

 recover in 1985, although species 

 composition had changed (Chapter 5). Dikes 

 that once separated the sewage lagoons had 

 been breached and widened (Chapter 6). The 

 islands in the main channel were obliterated 

 by the sand washover of 1983. The mouth was 

 artificially cut; and south of the new mouth, it 

 is clear that the beach line had moved inland. 

 What was once a shallow embayment became 

 the beach line, and only a narrow channel 

 remained. Control of vehicle traffic along the 

 urban periphery of the estuary had allowed 

 some vegetation regrowth. 



Disturbances that occurred south of the 

 estuary mouth in the 1960's left scars that 



1 8 



