(b) Karsh developtrent v/ill replace other habitats -- habitat of value to 

 wildlife will be replaced with a different habitat also of value to wildlife. 

 Reliable techniques for corrparing the various losses and gains associated with 

 conversion of one habitat type to another are in the developr^ental stage. 

 Often, it is difficult for local authorities to reach a consensus on relative 

 habitat values. 



(c) Release of contarpinants fron the dredged rraterial to the biota is a 

 concern — the potential that plants or anin:als rray take up and release con- 

 taninants to higher trophic levels will be discussed in greater detail in the 

 section about contaminant uptake. 



(d) Subsequent deposition of dredged material on artificially created 

 marshes is limited — development of a marsh will usually preclude the subse- 

 quent use of that area as a disposal site. Often, State and Federal regula- 

 tions and public opinion will prevent further disposal in wetlands. In con- 

 trast, many open water and confined disposal sites can be reused. Exceptions 

 may occur in areas of continued erosion or where the initial disposal created 

 a low marsh and subsequent disposal would create a higher marsh. 



A marsh can be developed in stages, thus increasing the number of dredging 

 cycles it can accommodate. By diking an area and utilizing cross dikes, one 

 compartment at a time can be filled over a period of years. 



Ecological considerations: In considering the addition of a marsh to a 

 local ecosystem, planners should consider the impact of the marsh on the total 

 ecosystem. For a discussion of ecological consequences of habitat development, 

 the reader is referred to Lunz et al. (1978). 



Site selection: Several factors should be considered in site selection. 

 The value of the aquatic habitat at the disposal site is a strong considera- 

 tion. Certainly, one should avoid seagrass beds, oyster beds, and other simi- 

 lar habitats. 



Low wave energy area"^ are best suited for marsh development. High energy 

 areas may require expens,.^ protective devices. Vincent (1£7£) described a 

 poorly chosen site located in a high energy situation, which also had poor 

 foundation conditions for construction of a protective dike. 



The distance that disposal material must be transported is of great im- 

 portance in site selection. In general, the greater the distance the greater 

 the cost. Equipment availability for long distance transport is also a factor. 

 For a thorough discussion of criteria for site selection see Environmental 

 Laboratory (r978) and Coastal Zone Resource Corporation (1976). 



Engineering considerations: Dredged material for marsh development can 

 either be confined or unconfined depending primarily on wave energy at the 

 site and the grain size of the dredged material. The higher the energy and 

 the smaller the grain size, the greater the need for protection. Hydraulically 

 placed clays and silts from maintenance dreding operations will usually re- 

 quire containment, regardless of wave or current conditions. Sand can tolerate 

 up to moderate wave energies without confinement (Smith 1978). Clay from "new 

 work" dredging often will not require containment because it will "ball" and 

 be resistent to erosion (conversation with R. T. Saucier, December 1979, WES, 

 Vicksburg, Mississippi.) 



44 



