ABSTRACT
An Innovative Approach to Development of a Regional Stormwater Management Facility
The paper will provide an overview of an innovative approach to the development of a regional stormwater management facility. The City of Edmonton is improving Whitemud Drive between 34 Street and Highway 14, and Associated Engineering was retained to design and oversee construction of the stormwater management system. Rather than simply design a system that accommodated the increased runoff from the improved freeway, it was designed to incorporate runoff from future developments in the upstream basin and reduce flooding downstream, and thus become a regional stormwater management facility for the City.

The land surrounding the Whitemud Drive site is largely undeveloped at this time. The Fulton Creek drainage course runs through the site, and was incorporated into the design. The stormwater management facility was designed to accommodate existing upstream runoff in the Fulton Creek basin, and also to mitigate flooding potential in the downstream basin due to future increases in runoff from the Free improvements and anticipated development. Environmental enhancement of the Fulton Creek drainage course was included in the design, and the new retention pond has been designed as an extensive wetland area for wildlife. The facility was designed to minimize operation and maintenance costs for the City. Material excavated for the wetlands area was utilized as borrow material for the freeway construction work.

KEYWORDS
Wetlands, Stormwater Management, Flood Protection.

INTRODUCTION
The City of Edmonton and Province of Alberta required large quantities of suitable earth fill material for the easterly extension of Whitemud Drive, a 4-lane (ultimate 6 lane) freeway with grade separations at a Highway (No. 14), CNR track and an arterial roadway. The project team seized the opportunity to use the excavation of borrow material to create a major regional stormwater management facility to serve a future 240 hectare (10,000 people) residential area with stormwater management. In addition, the regional stormwater management facility provides immediate flood control for existing developments downstream, reduces the size and cost of future downstream flood control works and removes a constraint to proposed developments.

Associated Engineering was engaged to develop the Fulton Creek Regional Stormwater Management Facility for the City of Edmonton. Through innovative and creative application of engineering principles, the above was satisfied as well as creating:

INTRODUCTION
Background
The City of Edmonton continues to grow and develop. Facilitating growth and development requires expanding the infrastructure necessary to serve this growth. The City has a responsibility to minimize the adverse social, economic and environmental impact of growth and to use limited resources efficiently and effectively and develop reliable and safe infrastructure systems.

The Fulton Creek watershed includes approximately 2,000 hectares of land upstream of the City boundary, and 1,300 hectares in the City of Edmonton. As development occurs storm drainage capacity constraints have increased the risk of flooding during major storm and snowmelt events in Fulton Creek.

Associated Engineering was engaged by the City of Edmonton to develop a Drainage Master Plan for the Mill Creek and Fulton Creek Basins in 1994. This Master Plan developed and assessed a number of solutions and recommended the strategic placement of stormwater management facilities along Fulton Creek to manage the flows and reduce the risk to life and property. Included was one or more facilities upstream of Whitemud Drive.

A key element in the planning for the basin was a recognition of the limited capacity of the creek and the high value that our society places on the environment.

With the extension of Whitemud Drive to Highway 14, there was an immediate need for borrow to construct three overpasses together with the need to control runoff from the freeway. The City and the design team recognized the potential to meet these immediate needs by constructing a regional facility that would provide a significant environmental resource and would also serve the long term stormwater management needs identified earlier.

Objectives
The objective of the Fulton Creek Regional Wetlands Facility was to create an environmentally enhanced recreational facility that would:

• provide a source of fill material for the freeway construction
• reduce the potential of Fulton Creek flooding lands downstream within the City of Edmonton
• control runoff from future residential and industrial developments.

The Solution
Engineering and environmental design principles were applied to create a 22 hectare regional stormwater management facility and wetland area. Approximately 700,000 m_ of excavated material was used to construct the freeway embankment plus two overpasses. In addition, 810,000 m_ of storage was created for stormwater management purposes.

The wetland was designed to:

• encourage diversity of natural habitats,
• serve as a regional recreational and wildlife viewing area
• enhance the quality of stormwater runoff released from the wetland
• control releases into Fulton Creek so as to reduce the risk of downstream flooding.

PRELIMINARY DESIGN
Regional Stormwater Management Pond Concept
The 1994 Drainage Master Plan for Fulton Creek identified a number of major drainage facilities required to reduce the flooding downstream as a result of a major storm event. Due to limited resources, the implementation of these facilities was not immediately possible.

In the fall of 1996, Associated Engineering was engaged to carry out the preliminary and detailed design of the storm drainage component of the Whitemud Freeway extension project.

The concept of a Regional stormwater management facility began to develop as the needs of the project’s participants were identified. They were:

• The Province of Alberta needed borrow to construct an overpass.
• The City of Edmonton’s Street Engineering Branch needed borrow to construct two overpasses.
• The City of Edmonton’s Drainage Services Branch needed to provide stormwater management for the freeway storm sewer system.

As the concept was further refined, additional benefits were identified including;

• The flood reduction facilities proposed further downstream on Fulton Creek could be relocated upstream saving significant dollars ($1.5 Million).
• The size of the facility lent itself to providing future stormwater management to service a residential population of 10,000 people.
• A major recreation and wildlife viewing facility could be constructed.
• Having a significant borrow source immediately adjacent the Whitemud Freeway also saved significant dollars ($1.5 Million).

A Value Engineering process was applied to the Regional Stormwater Management Pond project and it confirmed overall project savings in the order of $3.0 Million.

Pond Design Basis
The preliminary level hydraulic analysis of the proposed drainage system was performed using OTTHYMO.95 for runoff generation and routing through the pipe system, culverts and ponds.

The design of the stormwater management facility consisted of laying out and developing the various system components, (pond shorelines, pond cross-sections, pond sideslopes, inlet structures, weir structures, outlet structure and the receiving streamcourse). Sizing the various components to convey the anticipated flows, was confirmed by computer simulation.

During the hydraulic simulations, each of the system components were evaluated and sized to meet all of the criteria, standards, assumptions and requirements of the project and the City of Edmonton.

The hydraulic simulations also confirmed the ponds ability to relieve the downstream flooding potential. The inlet structure was designed to accommodate the maximum flow rates while the outlet structure was developed to control outflow from the pond to well below the predevelopment rates or drawdown rates.

A summary of the flow conditions for the Regional Stormwater Management Pond are given in the Table below.

In addition to the City design storms, historical storm events (1937, 1978 and 1988) and the 1:100 year, 6, 12 and 24 hour storms were analyzed to ensure the pond has the capacity and the capability to contain these highly unlikely events. The resulting time to peak and normal drawdown is given in figure 4.

The outlet structure for the pond was also designed with a rapid drawdown capability in the event of highly unlikely storms or two or more large events occurring in rapid succession. The rapid drawdown can be initiated by opening a 1200 mm slide gate, however, the maximum outflows during rapid drawdown are still less than the current predevelopment release rates.

Wetlands Concept
The facility is a radical departure from the traditional stormwater management pond in the City of Edmonton in terms of its size, scope, performance and intended use. The pond is substantially larger than any similar facility in the City and is unique in the intent to create a natural wetland ecosystem instead of a more traditional, manicured pond. The challenge was to design and build an engineered facility that would incorporate all the best features of a natural area within an urban environment with minimal maintenance required. Current City criteria for stormwater ponds provided little guidance as they were developed for a more traditional approach. Consequently, the "natural" area had to be "engineered" from "the ground up".

Specific components considered in the innovative design of the stormwater pond, to create a more naturalized environment are:

• the shoreline and slopes varied in consistency, size and configuration to create separate habitat zones.
• a terrace was located above the frequent flood elevation to allow future residents access to the facility, yet separate the people from the nesting and waterfowl areas.
• key plantings of specific plant species were proposed to enhance the variety of plant life and waterfowl (see figure 6).

• islands were created to provide naturalized nesting areas away from predators.?extensive low and high marsh areas were developed to promote opportunities for submerged plant life to propagate.
• shore planting was selected to reflect the potential frequency of flooding, for example:
  • less than 5 year flood event, willows and other marsh vegetation
  • above the 25 year flood event, spruce and deciduous trees.

The outfall from the stormwater management facility was also constructed in a manner that enhanced the natural characteristics of the facility. The existing Fulton Creek was lowered and realigned to accommodate the new wetlands facility. The alignment was field selected to create a natural, meandering streambed with varying sideslopes and channel widths. The channel alignment meandered between tree belts to minimize the disruption to the indigenous vegetation and leave the channel as natural as possible. In addition, wetlands were created along the way to enhance vegetation and wildlife varieties.

In addition to the emphasis that was placed on creating a natural environmental preserve, the facility had to be designed in a practical manner to accommodate the stormwater management requirements of the project. The facility had to accommodate major storm runoff from future residential areas, as they developed over the next 20 to 30 years. In addition, the facility had to contain major flood events within Fulton Creek to minimize the downstream risk of damage, flooding and loss of developable land. An outlet structure was specifically designed to provide a slow natural release, while providing an emergency drawdown capability for extreme storm events. The normal 30-day drawdown after a major event (in excess of a 1:100 year) can be shortened to 10 days, depending on rainfall conditions.

PROJECT IMPLEMENTATION
Implementation
The implementation of this project was difficult due to a variety of competing (sometimes conflicting) objectives and project needs. All of these had to be balanced at all times, while keeping the critical objectives of this facility in focus. The objectives in order of priority are:

• provide construction materials for the extension of the Whitemud Drive project
• construct a regional stormwater management facility
• create a wetlands and environmentally sensitive design that will enhance future use of this facility
• reduce operation and maintenance costs
• provide all of the above in the most cost-effective manner.

Another difficult challenge occurred in that the design for the facility changed frequently due to the changing perspectives of the related roadway projects as they evolved through preliminary design to construction, especially due to significant changes in the volume of borrow required for the roadway.

When the stormwater management facility was originally tendered, a total volume of excavation of 1,200,000 m_ was expected. By the time the project was complete, however, these volumes had decreased by almost half to approximately 700,000 m_.

The pond was completely re-designed three times to accommodate the significant changes in earthworks volumes. Yet at all times, the primary objectives could not change. Care was taken to ensure that the environmental objectives were not lost and that the facilities could still provide sufficient capacity for stormwater management. Refinements included:

• a reduction in deep water areas
• significant increases in marsh land areas
• a creation of additional islands which were both functional and compatible with the stormwater management and environmental objectives.

All of these issues were managed to create an effective, efficient, safe and reliable facility.

Project Management
Project Management was key to the success of the project to control the changing scope while maintaining objectives, schedules and costs. The project scope changed from two largely independent roadway projects to a highly integrated project including the regional stormwater management facility.

The project was fast-tracked to meet schedule deadlines. The Value Engineering process provided the confirmation of the design concept which allowed the project to proceed quickly though predesign, design and into construction.

The integration of the project and the significant scope revisions increased the risks to the project. Additional approving authority requirements, land acquisition requirements, expansion of the Environmental Screening Report and increased coordination with many agencies, departments and stakeholders were needed for the project to proceed. Due to the cooperation and work of all stakeholders, the additional tasks were overcome very quickly allowing the project to proceed.

CONCLUSION
The Fulton Creek Regional Stormwater Management Facility is the first facility of its kind in Edmonton. Intended initially as a source of earth fill for roadway construction, it evolved into a regional stormwater management pond that will be virtually indistinguishable from a natural wetland. It provides:

• 22 hectares of habitat for nesting waterfowl, birds, and wildlife.
• 700,000 m_ of borrow material for the eastward extension of Whitemud Drive.
• 810,000 m_ of storage for stormwater management to serve a future residential population of approximately 10,000 people.
• a naturalized method of enhancing the quality of runoff from the future urban area.
• a major recreational and wildlife viewing area of regional significance.
• reduced risk of flooding in Fulton Creek downstream.
• an overall cost saving to the City of Edmonton in the order of $3 million dollars.

The ability to integrate a number of different projects, coordinate between various City departments, levels of Government and stakeholders, fast-tracked the entire concept development, predesign, design and approval process to within 10 months while developing the first major facility of its kind in Edmonton is a tribute to all involved.