This is essentially a visual tour of a small 25 km2 watershed, last glaciated some 10,000 years ago, as seen from the perspective of an engineer charged with the responsibility for bringing about a reasonable degree of protection for residents of the alluvial fan traversed by the lower reaches of Cascade Creek. The principle focus is on aspects which impact significantly on the residential area.
Cascade Creek is situated at the northerly end of the agricultural Hatzic Valley, some 70 km east of Vancouver, B.C., and ranges in elevation from 1,360 m down to 100 m GSC where it discharges into Slave Lake. The watershed is comprised of two characteristically different areas: the Upper Watershed and the Lower Watershed.
Between 1950, when logging of the Upper Watershed commenced, and 1983, some 56% of this area was logged, in addition to which a wide transmission line R/W was cleared and an extensive network of logging and hydro access roads constructed. During clearing of the Hydro R/W in 1974, a slash burning operation got out of control and burnt a further 13% of the Upper Watershed. These various activities together have resulted in effective clearing of about 75% of the area.
Problems in the watershed first became significant in 1977 (Nov. 1) following moderately heavy rains (76 mm/24 hr. at Aggasiz): but during a period when the Nov.-Jan. total precipitation was 55% higher than the 57-year average. The total runoff for the adjacent Norrish Creek was also 55% above its 21- year average during this period.
Many instances of mass wasting, debris torrents and surface scour in the upper areas resulted in massive deposition of gravel and wood debris in the mainstem channel, causing severe damage in the lower, inhabited reach where the channel, choked with gravel at various locations, overflowed its shallow banks.
Subsequent storms during 1982 (Dec.), 1983 (Jan.) and particularly 1984 (Jan.) when 114 mm of precipitation fell in 24 hours at Aggasiz, resulted in recurrences of these problems to varying degrees.