the salmon river watershed - Learning Centre

Two isolated aquifers have been identified in the northern portion of the valley, a smaller
surface and a larger deeper one below. The lower aquifer is thought to be isolated by
geological formation from the upper one and the upper aquifer may exchange relatively freely
with surface flows in the river above (Pers. comm., A. Kohut, BCE, Victoria). Maps of these
aquifers have been developed based on available groundwater records (well logs) and may
soon become available to the SRWR in hard copy or perhaps in digital format (M. Wei, BCE,
Victoria, pers. comm.). Similar information is not available for headward portions of the valley
at the present time. Information collected by BCE indicates that there is no significant long
term decline in groundwater flow based on sample sites located at the south end of the
Salmon Arm Valley physiographic subdivision (Pers. comm., A. Kohut, BCE, Victoria).
Surface flow varies along the river in relation to geology, inflow sources and outflow sources.
Important outflow components include natural losses and human use withdrawals. Obedkoff
(1976) presented an insightful assessment in 1976 of the streamflow regime of the river
including perspectives on the relative bearing of groundwater and surface water inputs, losses
and withdrawal demands on fisheries resource requirements at low flow. This study
documented significant interaction between ground and surface water indicating a need to
consider both as a single resource. This was reiterated by A. Kohut, BCE at a public meeting
presentation given at Falkland in 1995 (SRWR).
2.4.2 Water Demand
Under the Obedkoff (1976) study (Figure 16) high irrigation demand periods (July-August)
were shown to correspond with low flow periods and critical time windows for salmon migration
and spawning activities. Aquametrix (1995) noted that 30-50% of the in-stream flow reduction
experienced during low flow periods in the Salmon River which are critical to spawning and
rearing life stages of salmon can be accounted for by surface water withdrawal for irrigation
and domestic purposes. Further to a 1954 (anon, DFO, 1954) realization that low flow period
water availability conflicts existed between irrigation demand and minimum fisheries
requirements, Obedkoff (1976) reiterated a need to manage water extraction to maintain
minimum flow requirements for sustaining salmon reproduction requirements. Two key
recommendations of Obedkoff et al. (1976) which remain unresolved are to:
• conduct a field survey of licensed water withdrawals to determine or estimate the quantity
of water withdrawn from the system
• establish a licensing system for groundwater, similar to surface water licensing
Present day hydrologic flow regimes are thought to have been affected by several key land
and resource use practices which have occurred in the watershed as a result of European
settlement. These especially include forest harvesting methods and agricultural practices of
the past 100-150 years (Fraser River Environmentally Sustainable Task Force, 1991; NW
Hydraulics, 1992; Aquametrix, 1995; Burt and Wallis, 1995; Miles 1995; Vadas, in prep). Mean
monthly discharge data collected by Water Surveys Canada for the period of record are
provided in Figure 17. Breakdowns of this data by Miles (1995) for three segments of the river
length from the uppermost station (Salmon River above Salmon Lake ) to monitoring stations
further downstream (at Falkland and near Salmon Arm) show an increase in mean annual
discharge (MAD) in a pattern from upper to lower watershed. A corresponding comparison
shows lower mean annual discharge per unit of drainage area in lower versus upper
watershed. A combination of natural and human related factors including elevation, snowpack,
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