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RICHMOND – The flood plain mapping for the Van Gaal drain north of Perth Street in Richmond has been washed away – for now.
At its meeting on Thursday, Dec. 17, the Board of Directors of the Rideau Valley Conservation Authority went against a staff recommendation to approve the flood plain mapping and voted to defer the matter to its January meeting.
This was done to provide more time to consider concerns expressed by a representative of Mattamy Homes, the housing firm which hopes to develop land adjacent to the Van Gaal drain. It may also help meet a request from city of Ottawa Rideau/Goulbourn ward councillor that revised mapping showing the impact on the flood plain of recently constructed earthworks along the Van Gaal drain be provided.
At the meeting, councillor Brooks said that he wanted to see a map showing the impact of the new earthwork berms on the flood plain mapping, claiming that consideration of the earthworks has to change the mapping. The flood plain mapping as presented by staff at the meeting addressed the situation along the Van Gaal drain without any earthworks present. The earthwork berms were built after the RVCA had done its flood plain mapping field work.
Councillor Brooks argued that the property owners of the land being impacted by the flood plain mapping are going to want to see what impact the earthwork berms will have on the proposed flood plain mapping.
“It has to have some,” councillor Brooks said.
Bruce Reid, director of watershed science and engineering services for the RVCA, admitted that there would be changes to the flood plain mapping north of Perth Street if the berms remain in place but said that no such revised mapping existed at present. Flood plain mapping for the Van Gaal drain south of Perth Street is already in force although there is one area of revision that the new flood plain mapping was going to address.
Councillor Brooks said that there was an understanding that besides the basic flood plain mapping, there would be a second step taken regarding the berms and their impact on the flood plain mapping. This view was backed up by Gisele Moore, secretary of the Richmond Village Plan steering committee, who confirmed to the Board of Directors that there was certainly reference to two maps, one showing the impact of the new berms, when the matter was discussed at the steering committee.
Mattamy Homes believes that the RVCA staff has been too conservative with some of its modeling parameters related to the new flood plain mapping.
One concern involves how the RVCA model addresses the flow coming from the wetlands which form the headwaters of the drain. Another concern involves the RVCA model’s approach regarding the ability of the adjacent land to absorb runoff. The RVCA model assumes corn as the crop on the adjacent agricultural land but crop rotation means that corn is the crop only once every three years. Other crops encourage less runoff and so the peak flow calculation should be adjusted for this.