Elnora Stormwater Management Plan
PROJECT. Stormwater Management Plan
LOCATION. Village of Elnora, AB
OWNER. Village of Elnora
Michelle White, CAO
START DATE. May 2012
COMPLETION DATE. Dec 2012
TAGISH’S ROLE. Prime Consultant
The Village of Elnora was faced with major problems in regards to their stormwater. The first portion of the report deals with the land directly west of the Village on the site of the decommissioned waste water management facility (WWMF), stormwater accumulates until the adjacent sewers backup and the lift station floods. The flooded area had no defined outlet and would continue to be problematic in all wet seasons. This flooding affects the existing infrastructure and future development as the land surrounding the decommissioned WWMF is slated for residential development.
The second portion of the report deals with minor stormwater issues identified by the Village. The first was a problematic water course that ran through the backyards of private homeowners. The second was a back alley that was flooding due to stormwater directed from an adjacent field.
In order to identify an adequate outlet, analysis of, LIDAR data, detailed surveys, historical photos and Village records were required. Researching the history of the Village was the key in finding out the historical outlet route, which in turn influenced the recommendation for the proposed outlet.
During operation of the waste water management facility there was no flooding around the facility. Prior to commissioning and after decommissioning there is always standing water. It is reasonable to assume that water infiltrated into the waste water treatment facility and was draining into ghost pine creek when the lagoons were released. Prior to the development of the lagoons the stormwater would have been trapped; but without any development adjacent to the pond area no damage would have been caused.
There was also an expansion area to the North that is slated for development and required hydraulic analysis to obtain the pre-development outlet rate. This area is riddled with natural attenuation influencing the pre-development outlet rate.
The pre-development rate calculated for the Annexed land to the North was applied to the land locked area on the decommissioned waste water treatment facility. Historical photos were used to identify a normal water level and the historical outlet; a new outlet was recommended just to the south of the flooding area under the CN Railway tracks, which is where it ultimately releases when in a flooded condition.
Utilizing the new outlet rate, the normal water level from the historical photos and the existing storage calculated from the contours. It was possible to route the 1:100 year 24 hour storm hydrograph through the pond to calculate the required storage and set a high water level for the pond. With the outlet in place the pond will only need to raise 0.30 m above the normal water level during the 100 year storm event.
The decommissioned waste water treatment facility will now be the stormwater management facility for a portion of the existing Village and the annexed land to the West. The annexed land to the north will be required to use some of its natural attenuation for the purpose of stormwater management and continue to release at 2.7 liters per second per hectare post development.
Problem Area 1 is located at the development between Queen Street and Main Street north of 6th Avenue. The recommended solution is for the Village to acquire a Right of Way through the affected properties and install a storm sewer to intercept the flows.
Problem Area 2 is located west of Queen Street and north of 6th Avenue. The recommended solution is to construct a channel through the open field from directly west of the Queen Street intersection to the large pond to the south (Decommissioned Wastewater Treatment Facility).
Conceptual Engineering Design
Conceptual Drafting and Design