| Abstract/Description or Keywords |
To assist in determining the factors which are affecting the recovery of the Tsolum Rivers once abundant Pink Salmon, changes in land use and river channel morphology from the 1930s through to the present were studied on the full airphoto record, from 1938 BC airphotos to 2005 Google Earth photos A field channel assessment from the Puntledge up to the Tsolums midelevation tributaries was done during late summer 2009 to determine current channel conditions. Water Survey Canada (WSC) flow data for the Tsolum River near Courtenay, as well as the neighboring Puntledge, were examined to determine if variations in yearly extremes of low and high flows were affecting spawning and in-river survival rates. Airphoto studies showed the first cut of forest development nearly done by the late 1960s. In the late 1950s and early 1960s the channel morphology underwent large changes, with mid-elevation boulder line morphology breaking down, in Murex Creek and the Upper Tsolum (Blue Grouse) tributaries most severely, to a lesser extent in Dove and Headquarters Creeks. High levels of aggradation, with channel widening, occurred in the lower Murex and Upper Tsolum above Murex in the early 1960s, with a huge fan at the Murex confluence. The timing of these channel changes coincides with the major drop in Pink salmon escapements. This wave of bed and bar material moved down the Tsolum during the 1960s and 70s, visible as deposits and widening nearly to Headquarters Confluence. A similar smaller wave of bedload entered the Tsolum from Dove Creek in the late 1960s. Lower Headquarters Creek, due to Wolf Lake, did not experience this pulse of bedload from its upper tributary. While re-vegetation of gravel bars has increased stability of some of the mobile bedload, higher average flows of the last two decades have slowed recovery. With the additional factor of ongoing bank erosion on the lower floodplain, pool depths are generally reduced through most of the system, from the estuary to upper tributaries, with the exception of a few noted locations. Spawner access to the upper system is slowed by aggraded lower reaches, and still nearly completely blocked to Murex and the Upper Tsolum by the deposits at the Murex confluence. Analysis of WSC flow records, and their relationship to escapements, shows a strong inverse relationship between the number of days of high flows and returns two years later, indicating the frequent movement of the unstable bedload affects the survival rates to out migration of incubating eggs. There appears to be a much weaker relationship between the average low flow, from Aug 15 to Sep 15, and the Pinks counted in that year, indicating some returning Pinks may go up the Puntledge if extreme flow conditions prevent access up the Tsolum. Recommendations include continuing lower floodplain bank stabilization and low flow enhancement, access improvement on a yearly basis by stream keepers, and some options for assisting in stabilization, revegetation, or reduction of mobile aggraded bars in the lower reaches of some of the tributaries and parts of the mainstem. It is recommended that channels of the Murex and Upper Tsolum to well below Murex be treated as highly peak flow sensitive. This project was co-funded by Living Rivers-Georgia Basin/Vancouver Island (2006-11), a program of the BC Living Rivers Trust Fund. |
