Knowledge CentreTechnical Resources SearchConference PapersENVIRONMENTAL MANAGEMENT OF AGED BRIDGE STRUCTURES IN PEI



Prince Edward Island (PEI) is located in Eastern Canada and comprises one of the four Atlantic Provinces. It has a population of 130,000 with a land area of 5,660 sq. km and boasts highly productive river systems and brackish estuaries fed from a network of stream and creeks flowing almost exclusively from ground water. In the early to mid-1950’s, the Province embarked on a new era of structure replacement, that included the then-popular creation of man-made fresh water lakes. At several watercourse crossing locations, aged large open-span bridge structures were replaced by constructing earthen road bed berms (i.e. causeways) complete with engineered hydraulic control structures which measured approximately 6.0 metres in span. This was the preferred method of structure replacement at that time since infilling was by far cheaper than replacing entire structural members. Coincident with the timing of this replacement program, land-based applications of fertilizers and pesticides to assist in farm crop production began to increase significantly. Approximately two or three decades following their installation, water quality issues began to emerge in the impoundments and waterways located upstream of most these control structures. In the worst cases, eutrophic conditions emerged in the upstream water bodies. The Province has recognized te need to consider removal of the control structures, and restoration of full tidal passage at these locations in conjunction with their Structure Replacement Program. Restoration of tidal passage at these locations has been accomplished successfully by a number of engineered methods including AASHTO girder bridges, pre-cast box span, steel box girders, etc. The Province has been replacing these structures on an ongoing basis since the mid 1980’s with significant, and surprisingly quick, beneficial effects on water quality and associated environmental components including socioeconomic and fishery resources. Today, a few such structures remain, with one of these slated for replacement this Fall of 2003. As part of their Structure Replacement Program, the Department assesses tidal passage requirements at structure replacement locations and also develops Environmental Effects Monitoring Programs to assess associated environmental criteria, such as Total Suspended Solids (TSS), before, during and after construction project to monitor and confirm the effects of the new structures. The integration of environmental management and design into the Department’s Structure Replacement Program has been a natural progression; one which has been very well received by regulatory agencies and the public

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Evans, D