The Pitt Meadows/Maple Ridge Diking District is located in the south central part of Pitt Meadows and southwestern corner of Maple Ridge. The Diking District includes 3546 hectares of land; 3136 hectares in Pitt Meadows and 410 hectares in Maple Ridge. The total drainage basin which contributes storm water runoff into the Diking District is 4062 hectares; 3535 hectares from Pitt Meadows and 527 hectares in Maple Ridge.
The Diking District is defined by the Fraser, Pitt and Alouette River dikes on the south, west and north boundaries respectively. The east Diking District boundary is defined by the rise of land in Maple Ridge at approximately 201 Street and the Canadian Pacific Railway alignment.
The 1970 Agreement between Maple Ridge and Pitt Meadows defined the boundary of the Diking District. This boundary was approximated by the floodplain definition of the day. The District of Maple Ridge has since refined the floodplain boundary. The adjustment includes that some properties that have been flood protected. The new floodplain boundary is defined by an elevation of 5.33 m. We assume this value originated from the 200-year floodplain mapping by the Provincial Government. This elevation defines the level of protection afforded by the Fraser, Pitt and Alouette River dikes. Figure 2 also defines 573 lots in Maple Ridge which are below 5.33 m elevation.
Floodproofing properties is a practise by various means typically protects habitable areas from floodwaters. Specific flood protection measures include; raising land; raising buildings, unique pumping arrangements, local dikes etc. These measures can successfully reduce the chance of flooding but are not substitutes for river dikes, regional pump stations and major slough and ditch storage areas.
Catchment boundaries are typically defined by topographic contour. Areas which naturally drain into downstream subcatchments are considered to be contributing flow to the downstream drainage area. These areas may or may not be in the floodplain. These areas may not directly require lowland drainage works such as dikes and pump stations to protect their lands from flooding. These areas do need a stormwater outlet. They do rely on lowland areas for part of their drainage solutions.
Typically, the drainage catchment area is larger than the floodplain area. These upland areas often contribute to the lowland flooding problems. The solution for lowland flooding often involves transfer of upland water through lowland areas to a suitable outlet such as the Fraser River. We will discuss the direct and indirect benefits of the Diking District works further in section 4 of this report.
The Maple Ridge/Pitt Meadows Diking District is comprised of four subcatchment areas. These catchments are the McKechnie, Cranberry, Kennedy Road and Baynes Road areas. The McKechnie Drainage Study defines this areas in detail.
The following summarizes the subcatchment drainage areas:
|Subcatchment Area||Total Area (ha.)||Major Outlet|
|McKechnie||792||Alouette River dike
McKechnie Pump Station
|Kennedy Road||2150 (301 from Maple Ridge)||Katzie Slough
Kennedy Road Pump Station and Floodbox
|Cranberry||441||Cranberry Slough Floodbox|
(226 from Maple Ridge)
|South Katzie Slough
Baynes Road Pump Station and Floodbox
Each community has various land use designations for properties in the Diking District catchment. The Official Community Plan for both Pitt Meadows and Maple Ridge suggest changes in land use in the buildout scenario. It is important to recognize that changes in land use can have a significant affect on the amount of stormwater runoff into the Diking District. As stated in the R.F. Binnie report a change of land use from agriculture to light industrial in the McKechnie drainage area will theoretically increase runoff flows by 19%. This may result in the need for upgrading the lowland drainage system in the McKechnie area. In other words, lowland drainage works are not always directly related to just area but must consider the various land uses to accurately assess the runoff rates and volume of stormwater. This will be further discussed in section five on alternative cost sharing strategies.