GwRech: An online tool for estimating groundwater recharge and groundwater discharge

Abstract GwRech is an online tool that allows for the estimation of daily groundwater recharge, groundwater discharge, and changes in aquifer storage. GwRech fills an existing gap regarding the availability of online and offline tools due to its ease-of-use, robustness and flexibility, and could serve as an alternative for more complex models, that might require extensive resources and expertise. GwRech uses an adaptation of the water table fluctuation (WTF) method for unconfined aquifers to estimate groundwater discharge and the change in aquifer storage based on the differences in daily water table elevations for consecutive days in conjunction with the specific yield of the aquifer. The modified WTF method developed for this tool allows for defining separate specific yield values for each stratigraphic unit in the vertical profile and thus allows for estimation of groundwater recharge and groundwater discharge in multi-layered aquifers. GwRech is freely available online. While subjected to the limitations in the applicability of the WTF method, and the current input-file limit of 7500 rows (i.e., ~ 20 years of daily data), GwRech can be used for any location for which the required input data is available. This technical note presents the development of GwRech and its conceptual model, online interface, operation guide, and limitations, as well as an example of its application using a 3-year dataset from wells installed at the Agriculture and Agri-Food Canada Harrington Experimental Farm (HEF) in Prince Edward Island (PEI), Canada.