USDA LTAR Common Experiment measurement: Overland flow v1

This is the authors' abstract. We don't add key points for this paper.

Overland flow is water that flows over a land surface (sheet flow) or in rills and gullies (concentrated flow) in response to rainfall or melting snow. Measuring overland flow on croplands and rangelands is important because it represents a key water pathway that controls pollutant losses from agricultural fields. When overland flow is accurately measured along with other water inputs and outputs, scientists can develop budgets describing how water and associated pollutants traverse cropland and rangeland systems. Tracking these budgets over extended time frames (years, decades) helps quantify the beneficial effects of improved agricultural management. In many edge-of-field and small watershed studies, overland flow measurements typically involve control structures such as flumes or weirs. Several hydrology textbooks and agency manuals (USDA, USGS) provide detailed guidance on weir and flume development, installation, and operation. In general, weirs and flumes are located at the outlets of drainage areas where overland flow exits an agricultural field. The devices are sized based on the range of expected flows. In most instances, weirs and flumes have preset equations that calculate discharge (the volume of overland flow leaving a field over a given unit of time) based on measurements of water height, or stage. A wide variety of sensors are useful in measuring stage in weirs and flumes, including floats, bubblers, and pressure transducers. Stage data from these sensors are then recorded at frequent time steps (seconds to hours) to provide continuous estimates of overland flow.