Abstract
Hydrology and hydraulics are forever coupled as the pillars of water management planning at mine sites and other mixed-use, rural-urban systems. Keeping the two components separate has long been the standard for estimating water quantity and designing infrastructure to manage it. However, separating the hydrological modeling from the hydraulic components does not capture the relationship between peak flows and facility flooding. By combining the hydrologic analysis with a one- (or two-) dimensional model allows the user to forecast flood conditions during design events and hindcast historical wet conditions.
The integrated hydraulic and hydrological components can also be used to simulate long-duration historical records. This task is typically achieved by developing logic-based simulation models in programs like GoldSim, where large timesteps and coarse datasets typically provide estimates on a daily, monthly, or yearly resolution. The combined hydrologic and hydraulic model that runs at a short timestep allows the user to calculate the runoff, infiltration, evaporation, and snowmelt relationships that vary on a second-to-second scale versus the traditional daily average.
The model technique aims to observe the effect of hydraulic conveyance and attenuation on the flooding of infrastructure at a mine site. The long-duration model is used to estimate annual inflows that report to specific facilities at the site.
The PCSWMM model uses a GIS interface to visualize catchments reporting to specific facilities represented by one-dimensional structures such as channels, culverts, storage areas, dams, and spillways.
The SCS Curve Number rainfall-runoff method was used to transform the rainfall hyetograph into a runoff hydrograph. The SCS method was selected because of the simplicity of the parameters. This site requires a simple runoff estimation because there has been inconsistent flow and water level monitoring at site. The available flow and level data was used to create a site inventory of water entering and being discharged from site in 2022. The deficit between the estimated runoff and the observed inflows was represented by a shallow groundwater and interflow module.
The application of typical runoff parameters coupled with a calibrated groundwater response resulted in a close representation of total site inflow over the course of a wet historical year. The model was calibrated to the 2021-2022 hydrologic year, and was validated across the 2022 calendar year. The resulting validation was within 2.2 % of observed inflows to the site.
This type of calibration may not accurately represent the exact proportion of runoff, groundwater, evaporation and losses, but it preformed well at predicting total inflow to a site that has a challenging mix of natural and disturbed catchments. The combination of the hydraulic and hydrologic components allowed the model to capture a complete picture of the site’s ability to capture, store, transport, and discharge water.
Authors:
Gordon Johnston | SRK Consulting Vancouver, Canada
Michael Dabiri | SRK Consulting Vancouver, Canada
Samantha Barnes | SRK Consulting Vancouver, Canada
Presenter:
Gordon Johnston | SRK Consulting Vancouver, Canada
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