At this time it is probably too early to seriously consider more drastic 

 solutions such as a redesign of the jetties. However, this may need to be 

 considered as part of long-range plans. Such a redesign should allow for the 

 impoundment basin to be enlarged in size and physically isolated from the 

 river-borne sediments. 



The area should continue to be monitored by the district. A regular 

 program of beach profile measurements should be taken once every 1 to 

 2 years for the next decade or so, to determine if long-term changes are 

 occurring near the mouth. The offshore bathymetry near the mouth should also 

 be occasionally monitored to determine the ebb shoal bar response to the 

 jetties. 



Lessons Learned for Future Weir Jetty Designs 



a. Good, reliable estimates of the longshore transport rate are needed prior 

 to jetty and impoundment basin design. The current recommended method 

 is to compute the long-shore transport rate from at least 2 years of onsite 

 wave data. Failure to have this will lead to uncertainties in anticipated 

 dredging costs, and may lead to poor choices in jetty and impoundment 

 basin design. 



b. Prior weir jetty systems have been located at inlets that typically have 

 minimal amounts of inland-derived sediments. This was not the case at the 

 Colorado River. In fumre weir jetty designs at river mouths that carry large 

 sediment loads, both beach and river sediments must be taken into 

 consideration. If the river-borne sediments are expected to pass through the 

 system without creating substantial shoaling problems, care should be taken 

 to situate the impoimdment basin so that minimal trapping of the river-borne 

 sediments occurs. This could be done through the use of retaining dykes, 

 by physically separating the basin from the river mouth, or by other creative 

 approaches. 



c. It is important for the project design to have flexibility to allow for 

 modifications of the size and shape of the impoundment basin based on 

 operational experience. 



Chapter 7 Discussion and Recommendations 57 



