DOI: 10.15482/usda.adc/28582658.v1
title: Data from: Calibration of V-notch and compound weirs for subsurface drainage water level control structures

description: 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<sub>CW</sub>, L s<sup>-1</sup>) was developed as: Q<sub>CW</sub> = a<sub>1</sub>(h<sup>b1 </sup>- h<sub>1</sub><sup>b1</sup>)+a<sub>2</sub>(W<sub>e</sub>-W<sub>v</sub>)h<sub>1</sub><sup>b2</sup> and compared with an existing equation available in the literature, Q<sub>V+R </sub>= a<sub>1</sub>(D<sup>b1</sup>)+a<sub>2</sub>(W<sub>e</sub>)h<sub>1</sub><sup>b2</sup>, where Q<sub>CW </sub>or Q<sub>V+R</sub> are discharge rates (L s<sup>-1</sup>), h and h<sub>1</sub> are heads above vertex/bottom and top of V-notch (cm), respectively, W<sub>e</sub> is the effective crest width of rectangular weir (cm), W<sub>v</sub> is the top width of V-notch (cm), D is the depth of V-notch weir, a<sub>1</sub> and b<sub>1</sub> are parameters for V-notch weir, and a<sub>2</sub> and b<sub>2</sub> 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 (NO<sub>3</sub>-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<sub>CW</sub> and Q<sub>V+R</sub>. The NO<sub>3</sub>-N load was obtained as the product of calculated tile discharge (i.e., Q<sub>V+R </sub>or Q<sub>CW</sub>) and NO<sub>3</sub>-N concentrations measured biweekly on grab samples. This dataset was used for comparing discrepancies in tile discharge and mass of NO<sub>3</sub>-N diverted to the saturated buffer based on the use of the two compound weir equations (Q<sub>V+R </sub>or Q<sub>CW</sub>) 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.<br>