CHARACTERIZATION AND EVALUATION OF PROPOSED HYDROLOGIC CRITERIA FOR WETLANDS

A wide range of criteria has been proposed for defining and identifyin g wetlands. This study was conducted to compare and evaluate seven pro posed criteria for wetland hydrology. The computer model DRAINMOD was used to simulate the hydrology for a range of drainage intensities on three soils in the North Carolina Coastal Plain. The threshold drainag e intensity for lands that barely satisfy each of the proposed criteri on was identified. Statistics characterizing the hydrologic and relate d attributes of these lands are presented. Results indicated that thre e proposed criteria (45/07, 45/14, and 30/14) characterize lands that are much drier than the other four criteria (5/15, 00/15, 15/21, and 0 0/21). (The first number indicates the depth in cm, and the second, th e number of consecutive days during the growing season that the water table must be less than that depth). Average annual water tables for t he first group range from 71 to 105 cm compared to a range of 43 to 74 cm for the second group. Relative wetness of lands satisfying each cr iterion was evaluated by predicting long-term average corn yields for threshold drainage intensities. Corn may be produced profitably on lan ds that satisfy the first three criteria. Lands that satisfy the secon d group of criteria are too wet for corn production. Whether a margina l site will satisfy given hydrologic criterion may strongly depend on definition of the growing season. It is recommended that the growing s eason be defined in terms of readily available, location specific temp erature data.