Characterization and evaluation of proposed hydrologic criteria for wetlands

ABSTRACT:

A wide range of criteria has been proposed for defining and identifying wetlands. This study was conducted to compare and evaluate seven proposed 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 drainage intensity for lands that barely satisfy each of the proposed criterion was identified. Statistics characterizing the hydrologic and related attributes of these lands are presented. Results indicated that three 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 00/21). (The first number indicates the depth in cm, and the second, the number of consecutive days during the growing season that the water table must be less than that depth). Average annual water tables for the 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 criterion was evaluated by predicting long-term average corn yields for threshold drainage intensities. Corn may be produced profitably on lands that satisfy the first three criteria. Lands that satisfy the second group of criteria are too wet for corn production. Whether a marginal site will satisfy given hydrologic criterion may strongly depend on definition of the growing season. It is recommended that the growing season be defined in terms of readily available, location specific temperature data.