Innovative Integration of Stormwater and Pump Station Systems for Advanced Stormwater Management
Overview
An innovative stormwater management solution for the Menifee Riverwalk Residential Development project sought to efficiently handle stormwater runoff in a space and power constrained environment. Working alongside the engineering team, Santa Fe Water System’s primary aim was to develop cost-effective, manageable stormwater infrastructure without compromising land use and system efficiency.
Stormwater Goals
The initial stormwater design, while straightforward, had significant land use implications. It involved allocating two acres for a biofiltration basin to handle a flow of 1.2 cfs for stormwater treatment. Recognizing the potential for land conservation, Santa Fe Water Systems proposed a more efficient alternative. This revised plan aimed not only to preserve valuable land but also to optimize the stormwater management process, offering benefits to both the community and various stakeholders. Central to the project’s goals was this dual focus on land conservation and enhancing system efficiency.
First, the objective was to mitigate a peak flow of 32.4 cfs entering from a combined site storm drain system to a manageable level of which 1.2 cfs would pump to a biobasin and 31.2 cfs would pump to an offsite drain. Due to the site’s elevation combined with the flow rate demand, a substantial pumping station would have been necessary to handle the volume and elevate the stormwater offsite.
Additionally, the electrical supply was limited to 208 V single phase, restricting available pump motor sizes. This, along with the mandate for effective stormwater management for varied storm events (notably the 85th percentile storm) and the need to optimize space and budgets, set the stage for a demanding project, and the need for a system that could balance efficiency, conserve acreage for recreational use, and work within a budget.
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Stormwater Solutions
A double-pronged approach was developed to address these challenges.
First, a comprehensive analysis of a 100-year storm hydrograph was conducted to understand the volume of water to be managed. This analysis led to the redesign of the storage solution, proposing an underground cistern to hold 65,000 cu. ft. of water to attenuate the peak 100-year flow, thereby reducing the pumped peak flow to 4 cfs. Furthermore, a proposed transition from a flow-based design to a volume-based treatment system reduced the treatment flow rate from 1.2 cfs to 25 gpm.
Second, in support of the volume-based design strategy, Santa Fe Water Systems introduced the use of a Modular Wetland System (passive flow biofiltration). This creative stormwater management approach presented a number of unique advantages:
- The volume-based proposal in combination with the biofiltration system, allowed for a reduction of the original required treatment flow rate of 1.2 cfs to 0.054 cfs.
- Reduced the size of the treatment area from a 2-acre footprint down to 81 square feet.
- Offered a reduction in the treatment and overflow pump sizes, saving on equipment and electrical demand. (The proposed smaller 1/2 HP treatment pump system would now be able to manage the 85th percentile DCV of 14091 cubic feet with a drawdown time of 72 hours, and the overflow pumps were reduced to 5 HP to handle 4 cfs versus the original 32.4 cfs.
- Allowed the site to still reach the volume and treatment mandates of the 85th percentile storm.
This optimized plan not only addressed the power and space limitations but also reduced the equipment and operational long-term costs. The utilization of smaller pump stations and a productive application of the Modular Wetland unit illustrated significant cost and space-saving while maintaining the efficiency and effectiveness of on-site stormwater management.
Results
The design followed a strategic methodology that included an initial design phase, a feedback-informed reevaluation, and a final design adjustment to factor in the electrical limitations and treatment volume requirements.
The outcome was a stormwater and pump system that seamlessly met electrical specifications and was both cost-effective and optimized. The changes now accommodate the electrical supply limitation as well as significantly decreasing the cost and space consumed at finish grade.
From a community perspective, there are now endless benefits and potential for the area above the cisterns, amenities like sports fields, parks, pickle ball courts, and more. For the stakeholders, from developers, engineers, to municipalities, the project delivered tangible benefits; saving land and system costs, while delivering a tailor-made solution that catered to site limitations.
The Menifee Stormwater and Pump System project stands as a showcase of adaptability, engineering acumen, and dedication to both community and environmental wellness.
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