Data from: Calibration of V-notch and compound weirs for subsurface drainage water level control structures

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 (Q_CW, L s^-1) was developed as: Q_CW = a₁(h^b1 - h₁^b1)+a₂(W_e-W_v)h₁^b2 and compared with an existing equation available in the literature, Q_V+R = a₁(D^b1)+a₂(W_e)h₁^b2, where Q_CW or Q_V+R are discharge rates (L s^-1), h and h₁ are heads above vertex/bottom and top of V-notch (cm), respectively, W_e is the effective crest width of rectangular weir (cm), W_v 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 Q_CW and Q_V+R. The NO₃-N load was obtained as the product of calculated tile discharge (i.e., Q_V+R or Q_CW) 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 (Q_V+R or Q_CW) 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.