Lower Duncan River Water Quality Monitoring (DDMMON-7). Year 2 Report. Report prepared for BC Hydro, Castlegar

Author: A.M.E.C. , Poisson

This report provides a two-year synthesis of the DDMMON-7 water quality monitoring program. The study aimed to address flow management issues including water temperature and total gas pressure (TGP) in the Lower Duncan River. Discharge and temperature data were entered into a Bayesian state-space polynomial proportional mixing model to assess the influence of reservoir operations on water temperature in the Lower Duncan River. Impacts of water temperature on three fish species of interest (kokanee, rainbow trout, and mountain whitefish) were also discussed.

– TGP concentrations exceeded 110% at spill discharges greater than ~60 m3/s during the 2010 and 2011 monitoring periods. TGP concentrations exceeded 115% at spill discharges greater than ~100 m3/s during the 2010 monitoring period and ~110 m3/s during the 2011 monitoring period.
– Modeling of mixing at a point in the LDR at km 2.55 below the zone where DDM and Lardeau River discharges meet, indicates that at DDM discharges 175 m3/s), but when the Lardeau River is between these two levels, there is some mixing predicted (20-40%). At DDM discharge >225 m3/s with mid-range Lardeau River discharges, 40-60% mixing is predicted.
– The influence of the LDR water temperature regime on kokanee (Onchorhynchus nerka) may affect the abundance of spawners present, spawning distribution, as well as timing of peak spawn and fry emergence.
– Water temperature was one environmental variable that potentially decreased rainbow trout (Onchorhynchus mykiss) egg survival during periods of dewatering in the DDM tailout spawning area, but observed temperatures were not outside optimal preferences for other life history stages of this species.
– The influence of DDM operations on water temperatures in the LDR may affect mountain whitefish (Prosopium williamsoni) spawn and emergence timing, since water temperatures were observed to be higher than optimal at the commencement of the observed spawning and incubation period.

– TGP concentrations exceeded 110% at spill discharges greater than ~60 m3/s during the 2010 and 2011 monitoring periods. TGP concentrations exceeded 115% at spill discharges greater than ~100 m3/s during the 2010 monitoring period and ~110 m3/s during the 2011 monitoring period.
– Modeling of mixing at a point in the LDR at km 2.55 below the zone where DDM and Lardeau River discharges meet, indicates that at DDM discharges 175 m3/s), but when the Lardeau River is between these two levels, there is some mixing predicted (20-40%). At DDM discharge >225 m3/s with mid-range Lardeau River discharges, 40-60% mixing is predicted.
– The influence of the LDR water temperature regime on kokanee (Onchorhynchus nerka) may affect the abundance of spawners present, spawning distribution, as well as timing of peak spawn and fry emergence.
– Water temperature was one environmental variable that potentially decreased rainbow trout (Onchorhynchus mykiss) egg survival during periods of dewatering in the DDM tailout spawning area, but observed temperatures were not outside optimal preferences for other life history stages of this species.
– The influence of DDM operations on water temperatures in the LDR may affect mountain whitefish (Prosopium williamsoni) spawn and emergence timing, since water temperatures were observed to be higher than optimal at the commencement of the observed spawning and incubation period.