humidity, is very clear. The coastal 

 haze, which usually reduces light 

 penetration, is absent, and both 

 evaporation and moisture stress become 

 extreme. 



south through the summer, eventually 

 closing off the entrance. Stream 

 discharges resulting from winter rain 

 break the sand bar near the river channel, 

 reinstating the pattern (Warme 1969a, 

 Macdonald 1976b). 



Table 2. Stream discharge at the Tijuana 

 River (Nestor gage). Watershed area 

 drained by this gaging station = 4,390. 



Acre- 



ft/ 

 Jan- 

 Mar Floods 



19 

 661 



no 



no 



no 



67,910 moderate 



20,620 minimal 



506,008* extreme 



average, 

 1937-80: 21,080 



•Estimated from upstream since 

 Nestor gage was destroyed by flood 



1.4 LAGOON CLOSURE 



Because tides are so important in 

 providing moisture for coastal marshes, 

 any interruption in tidal circulation can 

 have drastic effects on these communities. 

 Many of southern California's coastal 

 wetlands have a tendency to become closed 

 to tidal flow through the formation of 

 sand bars across their ocean connection. 

 Longshore currents move sand along the 

 southern California coast, so that 

 entrances to estuaries and lagoons are not 

 stable. Aerial photographs through time 

 show that entrance locations migrate, and 

 historical records document that many 

 entrances close off entirely for variable 

 periods of time. A typical sequence at 

 Mugu Lagoon is for the sand bar to migrate 



The cross-sectional area of lagoon 

 entrances correlates with the tidal prism 

 (i.e. the total volume of water moving in 

 and out of the embayment) according to 

 Inman and Frautschy (1966). As tidal 

 prisms are reduced through sedimentation 

 or filling for road construction or 

 development, the likelihood of closure 

 increases. Gravel, brought into the 

 mouths of lagoons during winter periods 

 when beaches are depleted of sand, may 

 accumulate and block the ocean connection 

 (W. Cayman, Oceanographer , Sea Science 

 Services, San Diego, CA). In addition, 

 restriction of lagoon entrances to a 

 single location, as under bridges along 

 the Pacific Coast Highway and railway, may 

 further enhance closure. 



The extent to which these embayments 

 closed prior to changes brought about by 

 man is difficult to determine, but local 

 geologists seem to agree that closure of 

 smaller lagoons was a natural phenomenon. 

 Man's intervention has no doubt increased 

 the tendency for closure as well as the 

 persistance of the sand bar blockage. 

 Study of Indian middens adjacent to three 

 San Diego County wetlands (San Elijo 

 Lagoon, Los Penasquitos Lagoon, Batiquitos 

 Lagoon and Agua Hedionda Lagoon) record 

 aboriginal use of molluscs which most 

 likely grew in the lagoons (Miller 1966). 

 Of these lagoons, only Agua Hedionda had a 

 living molluscan fauna (74 species) during 

 the study. The remaining three were 

 closed to the ocean and did not support 

 any living molluscs due to their brackish 

 (San Elijo) or hypersaline (Los 

 Penasquitos and Batiquitos) condition. 

 Middens next to the three closed lagoons 

 consisted of molluscs now found at the 

 well- flushed Agua Hedionda Lagoon. 



While open to tidal circulation, 

 coastal marshes are ordinarily wetted by 

 sea water (salinity ca. 34 ppt) , since 



