BUILDING A HYDROGEOLOGICAL CONCEPTUAL MODEL OF A WATER-STRESSED AGRICULTURAL WATERSHED

Groundwater is an important shared resource used for food production in agriculture and water supply for rural residents. Increasing populations and agricultural activities contribute to concerns about the sustainability of groundwater resources in certain areas of Southern Ontario. Long-term water management is an important practice to sustain adequate quantities for multiple uses. This research aims to provide a better understanding of the temporal and spatial variations of groundwater quantity in a water-stressed agricultural context.

The research site is located in the Lower Whitemans Creek subcatchment (65 km²), part of the Grand River watershed, within Brant County, Ontario, Canada. The site has low relief topography (360 to 254 masl). The local aquifer comprises the shallow and unconfined Norfolk Sand plain. Local specialty and cash crops have a high irrigation demand. The site is instrumented with 10 groundwater monitoring wells of various depths, two electrical conductivity-temperature loggers and two stream gauging stations in Whitemans Creek. Various techniques were used to characterize the site geology (drilling and analysis of soil cores, sieve analysis, slug tests, double ring infiltrometer and pumping tests). A survey was conducted to better understand regional farming practices. Groundwater and surface water has been sampled monthly since November 2015. The water samples were analyzed for natural tracers (electrical conductivity and 222-Radon) to estimate the location of groundwater inflow into the creek. Stable isotopes of water (δ¹⁸O and δ²H) were quantified to determine the origin of the water (precipitation, groundwater, surface water). The electrical conductivity activities in the surface water range from 0.713 mS/cm to 3.224 mS/cm, and from 0.948 mS/cm to 6.462 mS/cm in the groundwater. The 222-Radon activities within the creek range from 6.62 Bq/L to 0.19 Bq/L, and revealed a major point groundwater discharge into the creek. A hydrogeologic conceptual model of the Lower Whitemans Creek subcatchment is developed. The groundwater dynamics are quantified. Results from the study will provide a better understanding of the hydrogeological dynamics within the Lower Whitemans Creek and will be used towards enhancing better long-term water management practices in rural regions.