The following are recommendations for 

 maintaining tidal circulation: 



• Tidal prisms should not be 

 reduced by fill within the intertidal 

 zone. 



» Unnatural sediment input should 

 be controlled upstream. Various 

 non-structural measures are available 

 to reduce erosion, including 

 prohibiting grading during the rainy 

 season and requiring that graded 

 slopes be stabilized prior to fall 

 rains. 



• An annual cycle of closure during 

 the dry summer and reopening 

 following winter rains is not 

 necessarily unnatural for a wetland, 

 unless that system historically 

 maintained an open inlet. Signs of 

 paramount concern are increasing 

 duration of closure and decreasing 

 water quality during the closed 

 period . 



• Tidal prisms can be increased by 

 removing fill and dredging channels, 

 discussed under section M. 



Altered Watershed Hydrology 



Just as modification of water flow 

 from the ocean side has a major impact on 

 coastal wetland, so can modification of 

 the stream drainage. Chapter 2 described 

 how the release of reservoir water nearly 

 eliminated a downstream salt marsh. 



Unnaturally long periods of 

 freshwater inundation killed halophytes, 

 leached soil salts, and allowed freshwater 

 marsh to replace salt marsh vegetation. 

 Excessive freshwater input is detrimental 

 to coastal wetlands. However, the impact 

 of excluding freshwater flow is less 

 clear. Fresh water is very important to 

 salt marsh species because of the stimulus 

 it provides for seed germination. Annual 

 species and species which lack vegetative 

 reproduction are particularly dependent on 

 freshwater input. However, direct 



rainfall and local impoundments may be 

 more important than runoff in an average 

 year. 



Experiences at the San Diego River 

 marsh (Zedler 1981b) lead to an important 

 recommendation: 



• Management of coastal wetlands 

 should be coordinated with management 

 elsewhere in the watershed. The 

 recommendation is particularly true 

 for water and sand management, but it 

 also holds for management of 

 waterborne fertilizers, pesticides, 

 and other toxins, whose impacts on 

 southern California wetlands are 

 little known. 



Dredging 



Major dredging projects have occurred 

 in the harbors of Los Angeles, Long Beach 

 and San Diego, and to maintain the ocean 

 inlets to a number of lagoons. Nearly all 

 of Agua Hedionda has been dredged to 

 maintain a source of cooling water for the 

 Encina Power Plant (Figure 49). Openwater 

 fishing and boating activities have 

 replaced marsh communities, but about 70 

 acres of eelgrass beds have developed 

 where marsh used to occur (Bradshaw et al. 

 1976). Where dredging is not too 

 frequent, the development of viable 

 aquatic communities can lessen the overall 

 reduction of natural resources. 



Since dredging of existing channels 

 is recommended as one way of increasing 

 tidal prisms, and since dredging is 

 necessary to create wetland habitat from 

 filled or other upland topography, 

 ecological guidelines are needed. 

 Unfortunately, little research has been 

 directed toward these needs. At least two 

 current plans, which are attempts to 

 mitigate losses of wetland habitat nearby, 

 call for the construction of intertidal 

 and subtidal habitats from higher 

 topography. In Los Angeles Harbor, the 

 Port District hopes to create a variety of 

 channel, beach and marsh habitats within a 

 five-acre parcel. On the west side of San 



90 



