Hydrologic models for altered landscapes

Understanding the hydrology of soils that have been drained is necessary for wetland restoration and in determining whether redoximorphic features are relicts of a former hydrologic regime. This study shows how two kinds of hydrologic models can be used to estimate the quantities of ground water entering a site, as well as compute long-term (40 years) records of water table fluctuations. A water budget was computed for a Carolina Bay wetland that had been drained for agriculture but was being restored to a wetland. Precipitation, potential evapotranspiration, surface outflow, and water stored in the soil were evaluated for a 13-min period to determine the amount of ground water entering the bay. A water table simulation model (DRAINMOD) was used at an additional site in NC to compute 40-year records of hourly water table fluctuations along a soil toposequence. The data were then related to percentages of redox depletions having chromas of 2 or less. The water budget showed that ground water comprised 35% of the total water input into the bay, indicating the site was functioning as a discharge area. Water table hydrographs were used to confirm the ground water inflow estimates as well as die estimate of potential evapotranspiration. The 40-year record of water table data obtained from DRAINMOD was summarized as the average number of times the soils at a given depth was saturated for 21 continuous days or longer. Historic rainfall data were selected from an area having the same rainfall distribution as found at the experimental site. The relationship between number of saturation events and percentage of redoximorphic features showed that some features were forming in soil horizons that saturated only four times within a 10-year period. These were not considered to be relict features because they formed during infrequent saturation events. (c) 2005 Elsevier B.V. All rights reserved.