Spray dredging applying a thin layer slurry of dredged material to the marsh
Mark A Ford, National Park Service, US
Thin Layered Marsh Nourishment
Dredged materials from periodic dredging events are sometimes broadcast onto the marsh, including the floating marsh, in a marsh nourishment effort. When possible, spray dredges are used. These dredges collect the material, mix it with ambient water and spray the slurry on to the marsh surface. The thickness of the applied slurry can vary from very light, which would primarily nourish the marsh with fresh sediments and light nutrient loads, or applied to the marsh surface at depths up to and around 30 cm. Thicker applications would be desired if there is a strong vertical elevation deficit due to high soil subsidence rates.
Dredging of nearby waterways would need to be conducted. Given the relative short distances the slurry can be sprayed, areas of application would need to be within fifty (50) meters of the dredging operation. Funding and permits would also need to be secured.
Thin-layered application of dredged materials can be very beneficial to the marsh. Applications of greater than 30 cm can bury an existing plant community too deep, thereby killing the vegetation and perhaps causing more harm than good. It is important to have close oversight as dredging contractors often will apply the slurry randomly to suit their desires, versus applying where the restorationist would prefer.