the salmon river watershed - Learning Centre
the salmon river watershed - Learning Centre
the salmon river watershed - Learning Centre
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Two isolated aquifers have been identified in <strong>the</strong> nor<strong>the</strong>rn portion of <strong>the</strong> valley, a smaller<br />
surface and a larger deeper one below. The lower aquifer is thought to be isolated by<br />
geological formation from <strong>the</strong> upper one and <strong>the</strong> upper aquifer may exchange relatively freely<br />
with surface flows in <strong>the</strong> <strong>river</strong> above (Pers. comm., A. Kohut, BCE, Victoria). Maps of <strong>the</strong>se<br />
aquifers have been developed based on available groundwater records (well logs) and may<br />
soon become available to <strong>the</strong> SRWR in hard copy or perhaps in digital format (M. Wei, BCE,<br />
Victoria, pers. comm.). Similar information is not available for headward portions of <strong>the</strong> valley<br />
at <strong>the</strong> present time. Information collected by BCE indicates that <strong>the</strong>re is no significant long<br />
term decline in groundwater flow based on sample sites located at <strong>the</strong> south end of <strong>the</strong><br />
Salmon Arm Valley physiographic subdivision (Pers. comm., A. Kohut, BCE, Victoria).<br />
Surface flow varies along <strong>the</strong> <strong>river</strong> in relation to geology, inflow sources and outflow sources.<br />
Important outflow components include natural losses and human use withdrawals. Obedkoff<br />
(1976) presented an insightful assessment in 1976 of <strong>the</strong> streamflow regime of <strong>the</strong> <strong>river</strong><br />
including perspectives on <strong>the</strong> relative bearing of groundwater and surface water inputs, losses<br />
and withdrawal demands on fisheries resource requirements at low flow. This study<br />
documented significant interaction between ground and surface water indicating a need to<br />
consider both as a single resource. This was reiterated by A. Kohut, BCE at a public meeting<br />
presentation given at Falkland in 1995 (SRWR).<br />
2.4.2 Water Demand<br />
Under <strong>the</strong> Obedkoff (1976) study (Figure 16) high irrigation demand periods (July-August)<br />
were shown to correspond with low flow periods and critical time windows for <strong>salmon</strong> migration<br />
and spawning activities. Aquametrix (1995) noted that 30-50% of <strong>the</strong> in-stream flow reduction<br />
experienced during low flow periods in <strong>the</strong> Salmon River which are critical to spawning and<br />
rearing life stages of <strong>salmon</strong> can be accounted for by surface water withdrawal for irrigation<br />
and domestic purposes. Fur<strong>the</strong>r to a 1954 (anon, DFO, 1954) realization that low flow period<br />
water availability conflicts existed between irrigation demand and minimum fisheries<br />
requirements, Obedkoff (1976) reiterated a need to manage water extraction to maintain<br />
minimum flow requirements for sustaining <strong>salmon</strong> reproduction requirements. Two key<br />
recommendations of Obedkoff et al. (1976) which remain unresolved are to:<br />
• conduct a field survey of licensed water withdrawals to determine or estimate <strong>the</strong> quantity<br />
of water withdrawn from <strong>the</strong> system<br />
• establish a licensing system for groundwater, similar to surface water licensing<br />
Present day hydrologic flow regimes are thought to have been affected by several key land<br />
and resource use practices which have occurred in <strong>the</strong> <strong>watershed</strong> as a result of European<br />
settlement. These especially include forest harvesting methods and agricultural practices of<br />
<strong>the</strong> past 100-150 years (Fraser River Environmentally Sustainable Task Force, 1991; NW<br />
Hydraulics, 1992; Aquametrix, 1995; Burt and Wallis, 1995; Miles 1995; Vadas, in prep). Mean<br />
monthly discharge data collected by Water Surveys Canada for <strong>the</strong> period of record are<br />
provided in Figure 17. Breakdowns of this data by Miles (1995) for three segments of <strong>the</strong> <strong>river</strong><br />
length from <strong>the</strong> uppermost station (Salmon River above Salmon Lake ) to monitoring stations<br />
fur<strong>the</strong>r downstream (at Falkland and near Salmon Arm) show an increase in mean annual<br />
discharge (MAD) in a pattern from upper to lower <strong>watershed</strong>. A corresponding comparison<br />
shows lower mean annual discharge per unit of drainage area in lower versus upper<br />
<strong>watershed</strong>. A combination of natural and human related factors including elevation, snowpack,<br />
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