LAR 512 – Fall 2002

 

PROBLEM #17 – BASICS OF DRAINMOD WATER TABLE ANALYSIS & MANAGEMENT

 

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Please review the attached wetland hydrologic evaluation of a depressional area in the upper coastal plain in Cumberland County, NC.   The Drainmod simulation used a Tomotley Series soil data base, Laurinburg, NC climatic data for 23 years, distance between drains of 2,682-feet, drain depth of 2.68-feet, and other site specific data.  The water table depth was simulated using Drainmod on a daily basis from January 1, 1966 through December 31, 1988.

 

The hydrologic criteria used by the Corps of Engineers is that wetland hydrology exists when the area is inundated or saturated to the surface continuously for at least 5-percent of the growing season in most years (50-percent probability of recurrence).  Saturated to the surface is normally considered to be saturated within 12-inches of the surface.  The 5-percent standard is applied to the growing season (Cumberland County growing season is considered to start on the 51st day and end on the 358th day of the year, therefore 5-percent of the growing season is 15 days).

 

  1. Print out the 23 yearly water table graphs and mark the beginning and end of the growing season.  Measure the length of saturated at or above a 12-inch depth using the 15 consecutive day standard.  Mark any event that equals or exceeds 15 days.  How many years out of the 23 yearly graphs have a hydrologic event that meets the wetland hydrology standard?  __________

 

  1. In other words, in an average year does a 15 consecutive day wetland hydrology event occur during the growing season?  __________ 

 

Now, review the thirteen goals, objectives, and concerns (Section 2) in “Pocosin Lakes National Wildlife Refuge Hydraulic and Hydrologic Study and Management Plan” dated June 1994.  Also, review the Description of the Study Area (Section 5). This document is contained on the library reserve shelf.

 

  1. Please explain the overall intent of the water management study?  _____________________________________________________________________________________________________________________

 


  1. Please explain how each of water control structures could be used to regulate the pocosin hydrologic conditions in the refuge?
    1. Existing canals?  _____________________________________________________________________________________________________________________
    2. Existing v-ditches?

_____________________________________________________________________________________________________________________

    1. Earthen dikes?

_____________________________________________________________________________________________________________________

    1. Flashboard risers?

_____________________________________________________________________________________________________________________

 

You probably noted that the US Fish & Wildlife Service was concerned about how their water management plan might affect adjacent farming operations and how to avoid damage to properties surrounding the refuge.  One of the adjacent corporate farms sued the US of America in 1997 alleging that the US Fish & Wildlife Service had taken their property by inverse condemnation starting in January of 1993 and continuing until trail in 2001.  Review a document entitled “Drainmod Computer Simulation Analysis and Crop Yield Projections, 1993 – 2000” (Kays, 2001) and answer the following questions.

 

  1. Conceptually how was the Drainmod analysis used to disprove the plaintiffs allegations?  _____________________________________________________________________________________________________________________
  2. Why did the farm land not drain properly even though pumping stations, channels, v-ditches, and flashboard risers were present?  _____________________________________________________________________________________________________________________

Daily Water Table 1966 Daily Water Table 1967 Daily Water Table 1968 Daily Water Table 1969 Daily Water Table 1970 Daily Water Table 1971
Daily Water Table 1972 Daily Water Table 1973 Daily Water Table 1974 Daily Water Table 1975 Daily Water Table 1976 Daily Water Table 1977
Daily Water Table 1978 Daily Water Table 1979 Daily Water Table 1980 Daily Water Table 1981 Daily Water Table 1982 Daily Water Table 1983
Daily Water Table 1984 Daily Water Table 1985 Daily Water Table 1986 Daily Water Table 1987 Daily Water Table 1988 Daily Water Table 1989