Methods to Evaluate Normal Rainfall for Short-Term Wetland Hydrology Assessment.

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Title: Methods to Evaluate Normal Rainfall for Short-Term Wetland Hydrology Assessment.
Author: Sumner, Jaclyn Patricia
Advisors: Dr. R. Wayne Skaggs, Committee Member
Dr. Randall K. Kolka, Committee Member
Dr. David L. Lindbo, Committee Member
Dr. Michael J. Vepraskas, Committee Chair
Abstract: It is assumed, but not proven, that wetland hydrology can be evaluated with single-season measurements of water table data, if antecedent rainfall is within a normal or drier than normal range. Four methods of rainfall analysis were compared to long-term records of water table levels to determine which method could be used to identify sites with wetland hydrology. Water tables were simulated by DRAINMOD for two sites in NC and collected manually for one site in MN. Single years from 40 to 45 years of long-term water table data records were evaluated and compared with results from long-term records. Plots with wetland hydrology had a water table within 30 cm of the surface, during the growing season, in at least half the years. Years meeting wetland hydrology were identified for each site. Normal rainfall was determined from using the 30th and 70th percentiles obtained from a WETS data set for the nearest available weather stations. The first two methods computed a 30-day moving rainfall total that was compared with a normal range of rainfall values obtained from the WETS data. The remaining methods used a 3-month period of antecedent rainfall approach along with the WETS data to determine through calculations whether a given period had a normal range of rainfall. Plots meeting wetland hydrology met it in over 90% of the years in the long-term water table data records at all three sites. For single-year data, the moving total methods provided the correct conclusion in less than 45% of the years that met wetland hydrology. The DAREM approaches, which used rainfall for the prior 3-month period, correctly identified plots with wetland hydrology in over 80% of the years. The results showed that when single-season data are used to identify wetland hydrology, then, in most cases, no more than two years of measurement will be needed to reach a correct conclusion, and in most cases a single season of data may be used. However, there may be plots that have significant periods of drought or wetness and it is imperative to study surrounding plots at the research site to obtain an overall wetland hydrology at the site.
Date: 2006-11-15
Degree: MS
Discipline: Soil Science

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