Weirs usually reduce water-level fluctuations, reduce the volume of water during tidal exchanges, 

 and moderate salinity changes (Chabreck 1967; Hoar 1975; Morgan et al. 1975; United States 

 Department of Agriculture 1976). The impacts on vegetation should be a high priority 

 consideration when weirs are planned as components of marsh conservation plans. Plant 

 community characteristics play a vital role in the productivity of coastal marshes (Craft and Smith 

 1986). In this study, plants beneficial to wildlife increased in abundance and in diversity. This 

 change was consistent with the landowner's objectives. 



Salinity 



Salinity was less upstream of the weir for 41 of the 56 monthly samples (Table 6). For 12 of 

 the 56 monthly samples, the salinity was the same upstream and downstream of the weir. The 

 salinity was greater upstream of the weir for three monthly samples. Salinity levels were smaller 

 upstream for all yearly averages (Figure 1). 



Use of Fixed Crest Weirs in Fresh Marshes 



Very limited use has been made of fixed crest weirs in fresh marshes. The results of installation 

 of this weir were consistent with the landowner's objective. In the future, greater water 

 management capability could be achieved with the use of variable crest water-control structures 

 when there is a need identified for a structure. 



Table 6. Salinity readings, in parts per thousand. 



