addition, exotics (sea rocket and ice plant, 

 Carpobrotus edulis) have invaded. 



Fencing has helped to protect the dunes 

 from trampling, but not all areas are fenced 

 or maintained. It is widely agreed that 

 additional dune stabilization is needed. 

 Attempts to rebuild the dunes with dredge 

 spoils began north of the mouth in 1985. 

 Although the reconstructed dune helped 

 protect estuarine channels from overwash 

 during the 1986 storms, there was 

 substantial erosion on the seaward side and 

 dune crest, and most of the transplanted dune 

 species died. Dune reconstruction south of the 

 mouth was attempted, but storms ravaged the 

 site before vegetation could stabilize the sand. 

 The activities currently underway include 

 fencing to reduce trampling and stabilize the 

 sand, thereby facilitating revegetation efforts. 

 Success will depend on how well the plant 

 cover develops before another major storm 

 occurs. 



• River channels. There are no 

 descriptions of the Tijuana River where it 

 meets the estuary. A riparian ecosystem 

 developed after the 1980 flood, and dense 

 vegetation is now present within the reserve. 

 Species composition and use by wildlife 

 remain unquantified. Many of the future 

 hydrologic changes that will occur at Tijuana 

 Estuary may have their greatest impact on 

 this habitat type. As sewage spills come under 

 control, streamflows will decline. Research 

 is badly needed to characterize the riparian 

 species and their habitat requirements. 

 Determining the best management practices 

 for this international river remains a major 

 challenge. 



The individual disturbances to each of the 

 above habitats may seem minor. Collectively, 

 however, they have shifted many features of 

 the estuary and led to the decline of several 

 native species. It would have been difficult to 

 predict that trampling and denuding the dunes 

 would be a major cause of the population crash 

 of clapper rails in 1984. The cumulative 

 impacts of denudation, sedimentation, mouth 

 closure, drought, hypersalinity, and sewage 

 spills have significantly altered the estuary. 



When Tijuana Estuary was part of a large 

 wetland resource base (i.e., through the early 

 1900's), it was probably a resilient system. 

 Occasional flooding would have eliminated 

 marine invertebrates and fishes, but the 

 effects would have been temporary, with 

 larvae re-invading from San Diego Bay 

 wetlands. Those wetlands have since dwindled 

 to one-tenth their historic acreage. The 

 populations (and genetic diversity) of many 

 wetland-dependent species dwindled along 

 with their habitat. The decline in both the 

 quantity and quality of wetland habitats 

 throughout the region has reduced the 

 resiliency of Tijuana Estuary. Recovery of its 

 historic biodiversity is unlikely without an 

 active restoration program to reconstruct the 

 tidal prism, return its marine character, 

 expand habitat acreage, and expand species 

 distributions. 



6.4 THE TIDAL RESTORATION PLAN 



The goals of restoration are to improve 

 tidal flushing enough to maintain an open 

 ocean inlet and to create and restore sufficient 

 habitat for the maintenance of estuarine 

 biodiversity. These goals are complementary: 

 excavating sediments that have washed into the 

 estuary will increase tidal flushing and 

 expand wetland habitats. Most of the 

 restoration work will be done in the southern 

 arm of the estuary, where past sedimentation 

 has been heaviest and where tidal flows are 

 most sluggish. 



6.4.1 The Restoration Planning Process 



In 1984, the State Resources Agency and 

 the State Coastal Conservancy provided 

 funding to map the Research Reserve using 

 30-cm (1 ft.) contours and to develop a 

 hydrologic model (Williams and Swanson 

 1987). This was followed by a 3-year 

 resource assessment and impact evaluation 

 process that was funded by the State Coastal 

 Conservancy in 1988. 



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