Hydrology 2023, 10, 22. https://doi.org/10.3390/hydrology10010022 www.mdpi.com/journal/hydrology Article Assessment of a Smartphone App for Open Channel Flow Measurement in Data Scarce Irrigation Schemes Menwagaw T. Damtie 1 , Marshet B. Jumber 1 , Fasikaw A. Zimale 2, * and Seifu A. Tilahun 2,3, * 1 Department of Hydraulic and Water Resources Engineering, Debre Tabor University, Debre Tabor 272, Ethiopia 2 Faculty of Civil and Water Resources Engineering, Bahir Dar Institute of Technology, Bahir Dar 26, Ethiopia 3 Department of Ecosystem Science and Management, Texas A&M University, College Station, TX 77840, USA * Correspondence: fasikaw@gmail.com (F.A.Z.); satadm86@gmail.com (S.A.T.); Tel.: +25-191-870-1064 (F.A.Z.); +25-197-850-1750 (S.A.T.) Abstract: Accurate water fow measurement ensures proper irrigation water management by allo- cating the desired amount of water to the irrigation felds. The present study evaluated whether the non-intrusive smartphone application “DischargeApp” could be applicable and precise to measure small canal fow rates in the Koga irrigation Scheme. The app was tested in unlined canals with fow rates ranging from 15 to 65 l/s using a 90° V-notch weir. The app is found to overestimate high fow rates. Another source of uncertainty is that the app employed a constant surface velocity conversion factor (C = 0.8) to compute discharge. The accuracy was enhanced by recalculating the measured discharge using a new surface velocity conversion factor that depends on depths. The new conver- sion factor decreased the errors of MAE and RMSE by 47% and 52%, respectively. Where channel and other optional measuring techniques are not available without interfering with the fow opera- tion conditions in place, the DischargeApp devices can be used to measure fows. The DischargeApp could be used to collect data using local citizens in data-scarce areas. This study suggested recon- fguring the DischargeApp with a new surface velocity conversion coefcient based on fow depths in feld conditions for beter performance. Keywords: DischargeApp; surface velocity; unregulated canal; water management; Ethiopia 1. Introduction Water is a potential constraint for food security problems in the global community. Even though agriculture is playing a vital role in ensuring food security, it contributes to the largest share of freshwater management problems [1]. A signifcant number of large- scale irrigation schemes in Africa have serious water management issues which need con- siderable improvement for the sustainability of the schemes. An accurate fow rate meas- urement is one crucial factor to improve the performance of irrigation systems by allocat- ing the desired amount of irrigation water to the right irrigation system components [2]. The Koga irrigation scheme is one of the functioning projects in Ethiopia that was developed to irrigate about 7000 hectares of land to improve the livelihood of the commu- nity in the project area [3]. Several studies have been undertaken in this scheme related to water management issues [4,5]. It was found [5] that one of the key constraints to distrib- uting a fair share of water in the Koga irrigation scheme was the absence of fow control structures at the quaternary canal level, where fow is not adequately controlled and reg- ulated. Since quantifying the actual amount of irrigation water supply is very challenging at these canals, suitable canal water measurement devices are required to simplify the operation of the system [6]. Boman and Shukla [7] explained that efective irrigation water management begins with accurate water measurement. Flow rate measurements help to ensure that the irriga- tion system is operating properly. The diference between the true fow and the fow as Citation: Damtie, M.T.; Jumber, M.B.; Zimale, F.A.; Tilahun, S.A. Assessment of a Smartphone App for Open Channel Flow Measurement in Data Scarce Irrigation Schemes. Hydrology 2023, 10, 22. htps://doi.org/10.3390/hy- drology10010022 Academic Editors: Genxu Wang, Hongwei Lu, Lei Wang and Bahman Naser Received: 7 December 2022 Revised: 6 January 2023 Accepted: 10 January 2023 Published: 15 January 2023 Copyright: © 2023 by the au- thors. Licensee MDPI, Basel, Switerland. This article is an open access article distributed under the terms and condi- tions of the Creative Com- mons Atribution (CC BY) li- cense (htps://creativecom- mons.org/licenses/by/4.0/).