Problem and Objective
Gull Lake in central Alberta was challenged by falling water levels from the 1920s to the 1970s. In 1976, Alberta Environment (AEP) implemented a stabilization system to pump water into the lake from the Blindman River via a pump house, 30-inch pipeline and canal. The pump house has three 480 volt pumps with a combined output of 53m3/minute (14,000usgpm) at pressures of up to 70 psi to overcome the dynamic and hydraulic head in the pipeline. Since the stabilization system was built, the lake has gone through various ups and downs in water level, but with the system, these variances have been held to a relatively narrow band.
Prussian carp (Carassius gibelio), a non native species and prolific invader of freshwater ecosystems, was first detected in south-central Alberta in 2000 and has expanded geographically at an exponential rate (Docherty 2016). Prussian carp have been documented in the Red Deer watershed (Docherty 2016, Ruppert et al. 2017), including the Blindman River (Jason Cooper pers. comm. November 20, 2017). There is considerable concern regarding the potential introduction of Prussian Carp to Gull Lake due to their ability to outcompete native species and associated impacts to fish, benthic species and their habitat (Elgin et al. 2014; Ruppert et al. 2017).
AEP retained ISL Engineering and Land Services Ltd. (ISL) of Red Deer to study possible ways to continue pumping without risking the introduction of carp into the Lake. ISL’s brief “desktop” study concluded there was no reliable way to do so. It looked at a number of esoteric deterrent methods but did not consider filtration. On October 31st, 2018, the AEP set a 5 year suspension of pumping for lake stabilization just as the lake reached the trigger level where pumping would have resumed.
AEP forwarded the ISL report to the GLWS. Our review indicated that filtration was not evaluated, although it appeared to be a potentially reliable and economical approach that we felt should be considered. The GLWS decided to evaluate filtration and came up with two potentially viable methods to manage the substantial sediments present in the Blindman River and reliably remove carp fry/eggs from Blindman water before transfer. The methods were the Geotube and the Forsta backwash filter.
From Executive Summary and Recommendations
The Forsta filter was better able to handle the sediment load of the river water due to the higher operating pressure and backwash capability