Drainage Water Management (Controlled Drainage)
Drainage Water Management (Controlled Drainage)
Definition
Drainage water management (DWM), also known as controlled drainage, is the practice of artificially manipulating the outlet elevation to manage the water table and discharge volume from a surface or subsurface agricultural drainage system. This is achieved either by regulating a pumped outlet or by using a water control structure in a drainage ditch, pipe main, submain, or lateral drain. The USDA NRCS practice standards (CPS) 554 and 587 provide technical guidance on the planning and implementation of DWM.
Purpose
The primary purpose of DWM is to reduce nutrient, pathogen, and pesticide loading from drainage systems into downstream receiving waters. Other purposes include improving productivity, health, and vigor of plants, and reducing oxidation of organic matter in soils.
How Does This Practice Work?
Unlike conventional free-draining systems that lower the water table (i.e., remove excess soil water) to the depth of drains, a DWM system lowers the water table only to the depth of the adjusted outlet elevation. Thus, under DWM, the water table must rise above the adjusted outlet elevation before drainage can occur. This allows for increased water retention and storage within the soil profile during periods when drainage is not required. Outlet elevations during the year should support the primary purpose of reducing nutrient/pollutant loss while supporting crop production. The general recommendations for management of control structures are as follows:
- Lower the outlet elevation in fall (Figure 1a) and again in early spring (Figure 1c) to enable drainage water to flow freely and to ensure trafficable conditions for field operations at least one week in advance of the respective operations.
- Raise the outlet elevation to within 6-12 inches of the field surface during times of the year where drainage is not required (Figure 1b).
- Raise the outlet elevation again after planting and spring field operations as specified in the water management plan (typically, within 2 ft. of the field surface). The intent of growing season DWM is to conserve some water in the soil profile for the crop to use later in the growing season (Figure 1d).
Where This Practice Applies and Its Limitations
Drainage water management is applicable to landscapes with systematic tile drainage on poorly or very poorly drained soils where the topography is relatively flat (< 1% slope) and uniform. The practice can be implemented in fields with steeper slopes if drainage laterals are installed on the contours or additional in-line control structures are incorporated in order to manage the water table at distances farther from the drainage system outlet. The operator must be able to manage the drainage system without affecting adjacent landowners. The practice can be used with any drain spacing; however, a narrower spacing may provide additional benefits if the DWM structure is intended to be used during the growing season or for practices such as sub-irrigation.
Fields with steep slopes, coarse-textured soils, or leaky layers below or around the drainage system pose challenges to maintaining the desired water table depth over a large area of the field. The existence of any of these conditions limits the applicability of DWM.
Effectiveness
On average, compared to conventional free drainage, DWM can reduce the loss of water by 3.7 in. yr-1 (27% percent) and nitrate by 11.9 lb. acre-1 yr-1 (46% percent). The effect of DWM on phosphorus loss is variable. Studies report that DWM can decrease dissolved and total phosphorus load by 0.04 lb. ac-1 yr-1 (35%). However, DWM may increase phosphorus losses in surface runoff, which may negate some of the benefits. Drainage water management can also provide benefits to crop yield, with reported yield increases between 0% and 5% for corn and soybeans across the Midwest region.
The benefits of DWM can be further enhanced by pairing the practice with other structural, agronomic, and management practices. Automation and remote access to control structures may also provide additional benefits such as ability to do more active management during growing season and time saving to the operators.
Cost of Implementing the Practice
Costs include purchase of the water control structure ($500 to $2,000 ea.), installation of the structure ($200 to $500), and management time. Automation of the structure is also possible (additional cost of up to $5,000 per structure). For every structure installed, expect to make two to four adjustments per year – two in spring to adjust the outlet elevation before and after planting, and two in fall to adjust the outlet elevation before and after harvesting. Economic analysis suggests that the cost of nitrogen reduction would range from $1 to $11 per lb. N removed assuming no yield benefit, while a 3% yield increase would lead to a likely net economic benefit to the producer.
Operation and Maintenance
The operation of control structures is explained above. The structures for water table control usually do not require major maintenance. However, it is highly recommended to grease the stoplog seals at least once a year and ensure there is no debris in the tracks or along the bottom of the structure. If the stop logs are not being used, it is recommended to store them in a weatherproof location.
References
USDA, NRCS. 2020. Conservation Practice Standard 554 – Drainage Water Management. Available at https://www.nrcs.usda.gov/sites/default/files/2022-09/Drainage_Water_Management_554_CPS_10_2020.pdf
USDA, NRCS. 2017. Conservation Practice Standard 587 – Structure for Water Control. Available at https://www.nrcs.usda.gov/sites/default/files/2022-10/Structure_for_Water_Control_587_CPS_Oct_2017.pdf
Frankenberger, J., McMillan, S., Williams, M.R., Mazer, K., Ross, J., and Sohngen, B. in review. Drainage water management: A review of nutrient load reductions and cost effectiveness. J. ASABE.
King, K.W., Hanrahan, B.R., Stinner, J. and Shedekar, V.S., 2022. Field scale discharge and water quality response, to drainage water management. Agricultural Water Management, 264, p.107421.
Frankenberger, J., Kladivko, E., Helmers, M., Sands, G., Jaynes, D., Fausey, N., Cooke, R., Strock, J., Nelson, K. and Brown, L., 2004. Drainage water management for the Midwest – Questions and Answers About Drainage Water Management for the Midwest. Purdue Extension Factsheet WQ-44.
Ross, J.A., Herbert, M.E., Sowa, S.P., Frankenberger, J.R., King, K.W., Christopher, S.F., Tank, J.L., Arnold, J.G., White, M.J. and Yen, H., 2016. A synthesis and comparative evaluation of factors influencing the effectiveness of drainage water management. Agricultural Water Management, 178, pp.366-376.
Williams, M.R., King, K.W. and Fausey, N.R., 2015. Drainage water management effects on tile discharge and water quality. Agricultural water management, 148, pp.43-51.
For Further Information
Visit the Controlled Drainage Page at https://transformingdrainage.org/practices/controlled-drainage/
Current Authors
| Vinayak Shedekar The Ohio State University shedekar.1@osu.edu Kevin King |
Mark Williams USDA-ARS mark.williams2@usda.gov |
Editing and Design
| Deanna Osmond NC State University |
Forbes Walker University of Tennessee |
Citation:
Shedekar, V., M. Williams, and K. King. 2023. Drainage Water Management (Controlled Drainage). SERA17 Phosphorus Conservation Practices Fact Sheets. https://sera17.wordpress.ncsu.edu/dwm-controlled-drainage/