LAR 512 – Fall 2002

 

PROBLEM #13 – CREATING A WATER BALANCE FOR A WETLAND BASIN

 

Close this page to return to the Problems page.

 

Download the spreadsheet for problem 13 in either native Excel or HTML format.

 

Stormwater wetland extended detention or retention basins frequently fail due to (1) lack of sufficient water inflow, and, or (2) failure to take into account water losses from seepage, evaporation, and evapotranspiration.  The exercise will deal with the basic components of preparing a water balance to determine the critical hydrologic aspects of the wetland basin.  Let’s evaluate the likely hydrologic performance of the solution to Problem #12, Question #2 for the wetland extended detention basin concept.

 

Let’s assume that the basin is sited in an upland valley in a Cecil Series soil with a depth to water table of 15-feet below the pond bottom.  The saturated hydraulic conductivity of the Cecil subsoil is 0.75-inches/day.  Using the attached excel spread sheet and complete the water balance:

 

  1. Under evapotranspiration column, modify the imbedded formulas by replacing the initial zero in the formulas with the total pool area in acres from Problem #12, Question #2.

 


  1. Under seepage column, modify the imbedded formulas by replacing the initial zero in the formulas with the total pool area in acres from Problem #12, Question #2.



 

  1. What happens to the water in the basin?  ______________________________________________________________________________________________________________________________________________________________________________________________________

 

  1. Now reduce the seepage rate (inches/day) until you have achieved a pond turnover of 30 times per year.  What seepage rate is required to achieve the turnover of 30 times?  ______________________

 

  1. What different design and construction options would you consider using to achieve the turnover of 30 times per year?  __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________