Considerations for Effective Sloping Land Drainage Systems1
- G. R. Benoit and
- J. Bornstein2
A 12-plot sloping land drainage study in East Franklin, Vermont is located on a model Cabot silt loam—a poorly-drained glacial till fragipan soil. The plots consist of all combinations of two depths (30 and 51 cm) and two spacings (61 and 122m) of surface drains (diversions) and three spacings (none, 30.5, and 61 m) of subsurface drains located 102 cm deep.
Drainage, soil water, and climatic data were used to evaluate a water balance equation for each drain for six selected drainage intervals. A seismographic analysis showed variations in soil depth as related to bedrock configuration.
The results showed great variation in drain performance between drains in the same interval and between intervals for the same drain. Wide differences observed between values for drainage plus soil water storage and rainfall minus potential evapotranspiration seemed to be related to initial soil water content, the gain or loss of soil water, and the magnitude of potential evapotranspiration. Greatest drainflow occurred from those subdrains located at points of shallowest soil depths with bypass flow occurring under the drains particularly during saturated conditions. A drainage system for wet sloping soil should include:
Surface drains for controlled removal of snowmelt surface runoff
Subsurface drains located at the top of bedrock dropoffs; i.e, zones where the bedrock is closest to the soil surface
Subsurface drains systematically spaced between the drains of item 2 to intercept bypass flow before it reaches downslope soil surface areas
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