Aug 22, 2024
USDA LTAR Common Experiment measurement: Discharge from artificial subsurface drains
- Gary W. Feyereisen1,
- Kevin W. King2,
- Kevin J. Cole3,
- Mark R. Williams4,
- Rob W. Malone3,
- David D. Bosch5,
- Claire Baffaut6
- 1USDA Agricultural Research Service, Soil and Water Management Research, St. Paul, MN;
- 2USDA Agricultural Research Service, Soil Drainage Research, Columbus, OH;
- 3USDA Agricultural Research Service, National Laboratory for Agriculture and the Environment, Ames, IA;
- 4USDA Agricultural Research Service, National Soil Erosion Research Laboratory, West Lafayette, IN;
- 5USDA Agricultural Research Service, Southeast Watershed Research, Tifton, GA;
- 6USDA Agricultural Research Service, Cropping Systems and Water Quality Research Unit, Columbia, MO
External link: https://ltar.ars.usda.gov
Protocol Citation: Gary W. Feyereisen, Kevin W. King, Kevin J. Cole, Mark R. Williams, Rob W. Malone, David D. Bosch, Claire Baffaut 2024. USDA LTAR Common Experiment measurement: Discharge from artificial subsurface drains. protocols.io https://dx.doi.org/10.17504/protocols.io.x54v92ewzl3e/v1
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it's working
Created: March 11, 2024
Last Modified: August 22, 2024
Protocol Integer ID: 97094
Keywords: Long-Term Agroecosystem Research, LTAR, crops, subsurface drainage, agricultural land, tile drain, water budget, water flow, sediments, off-site movement, USDA LTAR
Funders Acknowledgement:
United States Department of Agriculture
Grant ID: -
Disclaimer
This research is a contribution from the Long-Term Agroecosystem Research (LTAR) network. LTAR is supported by the United States Department of Agriculture. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the United States Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable. USDA is an equal opportunity provider and employer.
Abstract
Subsurface drain discharge, sometimes simply referred to as drainage, is a process by which water is removed from a soil profile or area (ASABE, 2015). On agricultural lands with intermittent high-water tables due to precipitation or melting snow, water is removed using artificial (generally referred to as tile) drains or ditches to allow timely field operations and protect growing crops from being waterlogged. This discussion is limited to artificial subsurface (tile) drain discharge. In agricultural regions where crop production requires artificial subsurface drainage, drain discharge can represent a substantial portion of the annual water budget. Thus, measuring this water flow is important in understanding the water use of crops and potential impacts on downstream water movement. The measurement of subsurface drain discharge, together with a measurement of sediment and water pollutants, provides an assessment of the losses of these constituents from agriculture to the environment. Tracking them over time quantifies the beneficial effects of improved agricultural practices.
Guidelines
Site considerations
Agricultural plots or fields with artificial subsurface drains are typically flat or have little slope. In some cases, subsurface drain discharge is measurable using a weir and depth gauge at the tile outlet, where it empties into a drainage ditch. Because of slope limitations, an access pit must often be dug at the edge of the plot or field down to the drain line (Lawlor et al., 2008). Hydrologic isolation of study plots, or groups of plots, needs consideration. If subsurface water flow into a site from the surrounding area is concerning, install a perforated drain around the site perimeter. Keep drainage water from this perimeter drain separate from the plot collection system and route it downstream. Accomplish further isolation of plots within a site by installing a plastic-lined curtain between each group of plots or between plots to reduce lateral flow between plots (Kaspar et al., 2012). Such curtains need installation depths below the drain lines. For additional recommendations, refer to the section titled “Placement and site maintenance” in the USDA LTAR Common Experiment measurement: Best practices for collection, handling, and analyses of water quantity measurements (Baffaut et al., 2024).
Materials
- Discharge can be measured in a few ways, depending on the site access and outlet elevations, the potential for submergence, and the availability of electricity.
- Discharge can be routed into a tipping bucket with a counter that registers tips of a known volume.
- Use weirs or flumes with the measurement of water depth (known as “stage”) recorded by floats, ultrasonic sensors, bubblers, or pressure transducers (Brakensiek, 1979; U.S. Dept. of Interior, 2001; USDA NRCS, 2022; Walkowiak, 2008).
- While this document is being written, radar sensors for stage measurement are being tested.
- Discharge can also be pumped from a sump through a mechanical or electromagnetic flowmeter with a built-in recorder or connected to a data logger.
- Sometimes area–velocity sensors using Doppler principles are used for backup measurement in submerged conditions; however, velocities less than 15 cm/s can result in inaccurate readings.
Data collection
Data collection
Measurement
- Subsurface drain discharge can increase rapidly in response to precipitation events, so the stage is recorded at short time intervals (seconds to hours).
- Most often, discharge measurement devices are connected to an electronic data logger, which records stage in the device as well as additional parameters of interest, e.g., temperature.
- Construct a simple measurement system with a tipping bucket connected to a simple tip recorder with clock-recording capabilities.
- See https://transformingdrainage.org/videos/monitoring-tile-drain-flow for a video review of various techniques for measuring subsurface drain discharge.
Site maintenance
- Maintain equipment in a pit or field enclosure such that flooding is avoided during large events and rodents are excluded.
- Summer maintenance includes weed control.
- Depending on local conditions, take preventive measures in autumn to avoid freeze damage to equipment and lines.
- It is good practice to visit a site after a large precipitation event to check for damage and download data.
Data processing and quality control
Data processing and quality control
Download data from datalogging equipment at an interval compatible with the importance of the project and the consequences of missing data.
Calibrate and check field equipment for accuracy regularly, e.g., from weekly to bi-annually, depending on the site visit interval and the propensity for issues with the equipment and site. Keep detailed notes of instrument calibration for subsequent data correcting.
Check stage data for missing values or potentially erroneous readings by visually inspecting time series plots of stage and discharge.
Calculate the subsurface discharge (the flow volume over a given unit of time) by inserting the stage measurements into a rating equation for the particular weir or flume in use.
Express discharge in units of volume per time, m3 s-1.
Refer to the section “Quality control” in the USDA LTAR Common Experiment measurement: Best practices for collection, handling, and analyses of water quantity measurements (Baffaut et al., 2024) for additional recommendations.
Data file formats and metadata
Data file formats and metadata
Keep data in a .txt, .csv, spreadsheet, or database format. Good practice necessitates maintaining backups physically in a remote location and/or in the cloud.
- Suggested metadata to record, depending on the situation, include: tile diameter, tile slope, drainage area, tile spacing, weir/flume size, stilling pipe size, equipment manufacturers and model numbers, and soil characteristics.
Recommendations for data collection
Recommendations for data collection
Table 1. Summary of recommendations for measuring subsurface tile drain discharge.
| A | B | C | D | |
| Attribute | Preferred | Minimum | Comments | |
| Spatial scale | Field and plots | Field and plots | ||
| Frequency | Year round at 1 to 10 minute intervals | Year round at 30 minute intervals | The frequency of measurement depends on the study purpose and the size of the drainage area | |
| Covariate metrics | Precipitation, air or water temperature, irrigation, water table depth | Precipitation, irrigation | These covariates are useful for data quality control and analysis purposes | |
| Chemical variables | If chemical export is of interest |
Protocol references
1. ASABE. (2015). Soil and Water Terminology. ASAE S526.4. ASABE St. Joseph , MI.
2. Brakensiek, D.L., H.B. Osborn, and W.J. Rawls. (1979). Field Manual for Research in Agricultural Hydrology. U.S. Department of Agriculture, Agriculture Handbook 224, 550 pp. https://search.nal.usda.gov/discovery/delivery/01NAL_INST:MAIN/12287461020007426
3. Kaspar, T. C., D. B. Jaynes, T. B. Parkin, T. B. Moorman and J. W. Singer (2012). Effectiveness of oat and rye cover crops in reducing nitrate losses in drainage water. Agricultural Water Management 110: 25-33. https://doi.org/10.1016/j.agwat.2012.03.010
4. Lawlor, P. A., M. J. Helmers, J. L. Baker, S. W. Melvin and D. W. Lemke (2008). Nitrogen application rate effect on nitrate-nitrogen concentration and loss in subsurface drainage for a corn-soybean rotation. Transactions of the ASABE 51(1): 83-94. https://elibrary.asabe.org/abstract.asp?aid=24229
5. Baffaut, C., Schomberg, H., Cosh, M. H., O'Reilly, A. M., Saha, A., Saliendra, N. Z., Schreiner-McGraw, A., & Snyder, K. A. (2024). USDA LTAR Common Experiment measurement: Best practices for collection, handling, and analyses of water quantity measurements. protocols.io
6. Transforming Drainage. (2017). Options for monitoring tile drain flow. https://transformingdrainage.org/videos/monitoring-tile-drain-flow
7. U.S. Department of the Interior, Bureau of Reclamation. (2001). Water Measurement Manual, 3rd. Ed. U.S. Government Printing Office, Washington, DC. https://www.usbr.gov/tsc/techreferences/mands/wmm/
8. U.S. Department of Agriculture, Natural Resources Conservation Service. National Engineering Handbook, Part 650 – Engineering Field Handbook. Washington, D.C. https://www.nrcs.usda.gov/conservation-basics/conservation-by-state/north-dakota/nrcs-engineering-manuals-and-handbooks
9. Walkowiak, D.K. (ed.) (2008). ISCO Open Channel Flow Measurement Handbook. Teledyne Isco, Lincoln, NE.