USDA LTAR Common Experiment measurement: Channelized surface flow discharge v1

Measurement of surface flow rate (discharge) is often needed for agroecological studies, whether to understand the movement of water itself or to estimate what flowing water carries (e.g., nutrients or sediments exported from cropland or grazing land). Water may flow over land in non-channelized ways (the subject of a different protocol) or be confined to discrete channels. The present protocol addresses channelized flow within the context of the LTAR Common Experiment (i.e., from fields or plots), recognizing that such flow occurs as a continuum from rivulets to open drainage channels and small streams; hence, the optimal discharge measurement method depends on channel size and other considerations. Since the US Geological Survey measures discharge from large drainage areas, this protocol is geared toward discharge measurements in headwater streams and ditches. Because the situations in which channelized discharge may need to be measured vary considerably across the LTAR network, we are not recommending a specific protocol but instead offering considerations for selecting measurement methods and published references with more information on various options.