In many instances, land disposal of dredge material creates mosquito-breeding sources. Due to the initial high water content and characteristics of the dredged material, shrinkage cracks occur in the drying process. These shrinkage cracks provide ideal habitat for the production of mosquitoes. Experience by mosquito abatement agencies has shown the use of chemicals to kill mosquito larvae in the cracks is very inefficient and generally not practical. Solutions lie in the water management and periodic manipulation of the surface of the deposited material. Disking the spoil material fills and closes the cracks. Drainage of storm water and keeping the elevation of the ground water below the shrinkage cracks also prevents mosquito problems.

Disposal Site Management

1. Provide ditches and/or water control structures for drainage of surface water. An engineering survey may be necessary.

2. Disking of the areas may be required to close shrinkage cracks.

3. Provide access roads that are capable of supporting maintenance, inspection and mosquito control equipment.

4. Areas designated for permanent water should be constructed and managed for mosquito prevention as necessary for the specific site. Generally, dense aquatic vegetation, algal mats and shallow water bring on mosquito problems.

5. Areas designated for wetland development (saltwater marshes) need ditches to romote and enhance tidal water circulation and/or water control structures (tide gates) to provide water management capabilities. The outboard levee system should be retained until sufficient drying has occurred and all necessary grading and ditching has been finished.

6. Retention of outboard levees and tide gates may be necessary or desirable for water management to prevent excessive production of mosquitoes.

7. Plan and fund a maintenance program for the area to provide for:

a. Maintenance of ditches and water control structures
b. Disking as necessary
c. Maintenance of levees and access roads
d. Occasional mosquito control with pesticides and/ora biological agent such as mosquito fish

The preceding mosquito prevention criteria are intended only to offer guidance when considering the development of design options during the planning process for projects. Be advised that these practices have been found to be effective, however, once the project has been completed it is essential that conscientious maintenance and management practices be followed to help ensure the successful prevention of mosquito production.

Be further advised that under the California Health and Safety Code (Sections 2274 et. seq.) the responsibility for the cost of mosquito control may fall on the property owner.