Edge-of-field conservation practices which treat subsurface drainage (“tile”) water such as saturated buffers and bioreactors use water level control structures to manage water levels and estimate drainage discharge. A weir is installed within the control structure to monitor water levels which is converted to discharge using relevant weir equation. In a control structure, it is unclear how to calculate discharge for different sizes of control structures, especially when the water level exceeds the top of a V-notch and overflows in the rectangular portion of the compound weir (CW). The discharge equation for overtopping events (QCW, L s-1) was developed as: QCW = a1(hb1 - h1b1)+a2(We-Wv)h1b2 and compared with an existing equation available in the literature, QV+R = a1(Db1)+a2(We)h1b2, where QCW or QV+R are discharge rates (L s-1), h and h1 are heads above vertex/bottom and top of V-notch (cm), respectively, We is the effective crest width of rectangular weir (cm), Wv is the top width of V-notch (cm), D is the depth of V-notch weir, a1 and b1 are parameters for V-notch weir, and a2 and b2 are parameters for rectangular weir.The dataset comprises of i) calculated values of daily subsurface drainage discharge rate that was diverted to a saturated buffer located at Break Creek site (BC2; 42.211284 °N and 93.470736 °W) in Hamilton county in central Iowa, US, and ii) the mass (and cumulative mass) of nitrate-nitrogen (NO3-N), in kilograms, diverted to the buffer during a two-year period from January 2016 to December 2017. The subsurface drainage discharge rates at the study site were obtained by monitoring water heads above 45° V-notch weirs within a 20.3-cm (8-in) water level control structure and were calculated using the two compound weir equations QCW and QV+R. The NO3-N load was obtained as the product of calculated tile discharge (i.e., QV+R or QCW) and NO3-N concentrations measured biweekly on grab samples. This dataset was used for comparing discrepancies in tile discharge and mass of NO3-N diverted to the saturated buffer based on the use of the two compound weir equations (QV+R or QCW) in the primary article.Resources in this dataset:Resource Title: NitrateLoad_Data.csv: Resource Description: Data compiled as a result of the efforts described in Katuwal et al.(2024) - Calibration of V-notch and compound weirs for subsurface drainage water level control structures.Resource Title: NitrateLoad_Data_Dict.csv: Resource Description: Data dictionary for the nitrate load as described in Katuwal et al.(2024) - Calibration of V-notch and compound weirs for subsurface drainage water level control structures.Resource Title: Subsurface_Drainage_Discharge_Data.csv: Resource Description: Data compiled as a result of the efforts described in Katuwal et al.(2024) - Calibration of V-notch and compound weirs for subsurface drainage water level control structures.Resource Title: Subsurface_Drainage_Discharge_Data_Dict.csv: Resource Description: Data dictionary for the subsurface drainage discharge as described in Katuwal et al.(2024) - Calibration of V-notch and compound weirs for subsurface drainage water level control structures.