Measurement of drain flow, soil moisture, and water table to assess drainage water management

Kyle Brooks, Purdue University

Abstract

The installation of subsurface drainage has increased in recent years due to improved economics of the practice. This is occurring as there is a growing need to decrease the amount of nutrients being exported to surface waters. One way of decreasing nitrogen loss from drained fields is by utilizing a management practice known as drainage water management (DWM), also referred to as controlled drainage. This practice has the potential to keep nutrients in the field, reducing their export through the drain usually by decreasing the amount of annual drainage by maintaining a higher water table in the field when possible. To better quantify the reduction of drain flow, very accurate flow measurement is needed which can be difficult due to extended periods of low flow, event periods with very high flow, and the possibility of submerged outlet conditions. In the monitoring site at Davis Purdue Agricultural Center (DPAC), there is one field divided into four quadrants around 3.6 ha each. Two fields use DWM while two are conventionally drained. Electromagnetic flow meters and soil moisture sensors were installed in October 2011 at the existing site where water table has been measured since 2006. These data were then analyzed over the time period of December 1, 2011 through November 30, 2012 to get an initial look at the effect DWM had during this time period. In this dry year, the managed fields had an average 40 mm or approximately 16% lower drain flow than the freely drained fields. The effect of DWM on the rate of water table recovery after a precipitation event was also analyzed using existing data from 2006 through 2011. In one pair of quadrants, the rate of water table recovery was significantly lower with DWM, suggesting that the reduced hydraulic gradient slowed drain flow. A longer period of a high water table could be detrimental to a growing crop or cause trafficability issues. The extensive network of equipment on the plots will enable a better understanding of the effect of DWM on the dynamics of the water in the field.

Degree

M.S.A.B.E.

Advisors

Bowling, Purdue University.

Subject Area

Agricultural engineering

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