HYDROTECHNICAL STUDIES OF PETERS RIVER

Peter's River in central Newfoundland supplies water to the town of Bo twood from an intake located at a point just upstream of a right-angle d bend. The pumphouse is situated on the outer bank of the river and i s constructed on a foundation of sandy silt. In 1983, a large flood er oded part of the bank and removed vegetation which had provided a prot ective cover. Progressive erosion then threatened the pumphouse and fo rced an engineering assessment of the situation. This was conducted in the winter of 1984-1985 and included the prediction of the 50- and 10 0-year floods from the minimal data (4 years of records) which were th en available. Estimates were made of velocities and flood levels, and various protection schemes were considered. The installation of a reve tment in 1986 stabilized the bank, but icing on the intake had always caused problems and these continued unabated. In winter, frazil ice ad hered to the submerged intake structure and was drawn into the pumps c ausing frequent shutdowns. Various solutions, including electrical hea ting, were considered. However, in 1991, a decision was made to instal l infiltration pipes below the stream bed, to raise water levels with a small broad crested weir and to disconnect the existing intake. Flow estimates were again required, both for construction purposes and for responding to the Department of Fisheries requirement that there woul d be no immediate or long-term harm to fish habitat. This paper provid es a brief description of the general problems, but focuses primarily on the methods used, 8 years apart, to estimate flood data. These meth ods were intended to be relatively unsophisticated, but were consisten t with the magnitude of the river and the relatively small scale of th e proposed works. In the study conducted in 1984-1985, only 4 years of records were available and the estimation of the 50- and 100-year flo ods relied strongly on the use of regional equations, the development of unit hydrographs, and one large recorded flood. The more extensive record available in 1991 permitted some more sophisticated statistical techniques. However, the large flood which occurred in 1983 still cau sed considerable difficulty, and the results of the analysis varied ac cording to how this flood was included. Despite these difficulties, it was shown that the estimates made in 1984 were not unreasonable.