Determination of lateral effects of borrow pits on hydrology of adjacent wetlands.
Advanced Search
Select up to three search categories and corresponding keywords using the fields to the right. Refer to the Help section for more detailed instructions.

Search our Collections & Repository

For very narrow results

When looking for a specific result

Best used for discovery & interchangable words

Recommended to be used in conjunction with other fields

Dates

to

Document Data
Library
People
Clear All
Clear All

For additional assistance using the Custom Query please check out our Help Page

i

Determination of lateral effects of borrow pits on hydrology of adjacent wetlands.

Filetype[PDF-1.76 MB]


English

Details:

  • Creators:
  • Corporate Creators:
  • Corporate Contributors:
  • Subject/TRT Terms:
  • Publication/ Report Number:
  • Resource Type:
  • Geographical Coverage:
  • Edition:
    Final report; Sept. 2004-Aug. 2007.
  • Corporate Publisher:
  • Abstract:
    A three year research project was conducted to develop and test a method to predict the distance borrow pits should

    be set back from adjacent wetlands to avoid detrimental impacts on wetland hydrology. The method is based on the

    Boussinesq equation. Knowledge of soil hydraulic properties and the time, T25, required for characteristic water table

    drawdown is necessary to calculate the setback. DRAINMOD simulations were conducted to determine the T25

    values for all 100 North Carolina counties. A survey of 27 borrow pits indicated seepage from the wetland to the pit

    in 42% of the pits, pit to the wetland in 31% and sometimes in one direction and vice versa in 27% of the pits. Eight

    borrow pits were instrumented to determine the response of the water level in the pit, and the water table in adjacent

    wetlands, to rainfall, evapotranspiration and seepage. The time required after closure for the water level in pits to rise

    to equilibrium varied from 10 to 23 months with an average of 17 months. The equilibrium water level is a critical

    factor affecting the impact of the pit on hydrology of adjacent wetlands. This depth depends primarily on the

    elevation of surface water outlets, the depths of adjacent drainage ditches or other subsurface drainage sinks in close

    proximity to the pit, and the natural depth of the water table prior to the construction of the pit. Equilibrium water

    levels in 5 of the 8 instrumented pits were lower than the surface of adjacent wetlands, with seepage from the wetland

    to the pit. The average water levels in the 5 pits ranged from 1.0 to 4.1 ft. below the surface of adjacent wetlands.

    Water level elevations in the other 3 pits were equal to or above the elevation of adjacent wetlands. The method

    developed herein was used to predict setback requirements for the 5 instrumented borrow pits having seepage from

    wetlands to the pit. Results were compared to the potential lateral impacts determined from measured water table

    data. The setback distances predicted using the measured pit water levels were about 60% greater than the measured

    impacts on average. The method is based on conservative assumptions so the overestimation was not unexpected.

    Use of a constant 2 ft. depth of water in the pit predicted setback requirements within 16% of measured potential

    impacts for 3 of the 5 cases; the setback was overestimated by more than a factor of 2 for the other two pits.

    However, the projected lateral impacts were less than 50 ft. in both cases. It was concluded that the proposed method

    will provide conservative but reasonable estimates of the setback necessary to avoid impacts on the hydrology of

    wetlands adjacent to borrow pits.

  • Format:
  • Collection(s):
  • Main Document Checksum:
  • Download URL:
  • File Type:

Supporting Files

  • No Additional Files
More +

You May Also Like

Checkout today's featured content at rosap.ntl.bts.gov