ABSTRACT
This chapter discusses the processes that add and subtract water from the wetland, together with the relationships between flow and depth. Internal water movement in wetlands is a related subject, which is critical to understanding of pollutant reductions. The water status of a wetland defines its extent, and is the determinant of plant species composition in natural wetlands. Hydrologic conditions also influence the soils and nutrients, which in turn influence the character of the biota. The ability to control water depths is critical to the operation of treatment wetlands. This operational flexibility is needed to maintain the hydraulic regime within the hydrologic needs of desired wetland plant species and may also be needed to tune the treatment efficiency of the treatment marsh. The important features of wetland hydrology from the standpoint of treatment efficiency are those that determine the duration of water biota interactions, and the proximity of waterborne substances to the sites of biological and physical activity.
