Muskrat damage may cause leakage of wastewater from the wetland and result in possible contamination of the surrounding soil or bodies of water. Control Structures Inlets control the flow of wastewater from the septic pre-treatment into the constructed wetland. An important property of the inlet is the degree to which it promotes sheetflow in an even distribution across the width and depth of a constructed wetland. The design of the inlet is in response to the size of the constructed wetland. In small systems a single-point discharge is adequate.
Outlets maintain sheetflow distribution, water level and monitor flow and water quality.
The outlet design can vary between a very simple and inexpensive design such as a pipe embedded in a berm, to a more expensive electronically monitered system of wier controls. Occasionally, beaver may cause system dysfunction by building dams near wastewater inlets. This damage may result in increased residence time of the wastewater, causing low oxygen conditions from the stagnant water. Plants and Planting Emergent wetland plants with regenerative capabilities are used in constructed wetlands. The general criteria of these plants are that they are fast growing, have high lignin content, and are adapted to variable water depths.