Low Impact Development Design

Evaluate the effectiveness of Low Impact Development (LID), green infrastructure and other best management practices for reducing wet weather pollutant loadings. LIDs are integral to new development design and are also being widely retrofitted into existing developments.

Low Impact Development (LID) is an increasingly popular alternative to "end of pipe" solutions. LIDs are designed to intercept, store and/or infiltrate precipitation before it reaches the conveyance system. LIDs are becoming an integral part of new development design and are also being retrofit into existing developments in order to promote infiltration, reduce storm water runoff and improve receiving water quality.

PCSWMM streamlines the modeling of LIDs on either a detailed, lot-level scale, or on a subwatershed or watershed scale for planning studies. The deterministic approach models physical processes within various LID control devices.

Supported LIDs include:

permeable pavements,
bio-retention areas and rain gardens,
green roofs,
rain barrels, cisterns with water reuse,
vegetative swales and buffer strips,
infiltration trenches, and more...

PCSWMM's capabilities for LID analysis include:

detailed, physically-based, lot-level LID design and evaluation,
master planning type studies, with quick assignment of multiple LIDs and treatment areas,
evaluation of the long-term performance of LIDs with clogging (reduction of infiltration capacity),
comparison of the continuous hydrologic and water quality benefits of various LID implementations with scenario comparison tools,
use of Sensitivity-based Radio Tuning Calibration (SRTC) tool to determine sensitivity of different LID practices and parameters under different conditions,
determination of effectiveness of LIDs for precipitation events of different types and timing using PCSWMM’s time series analysis/management tools (to evaluate reduction in peak runoff, total flow volume, pollutant load etc.),
analyzation and comparison of results with flow-duration-exceedance curves, and more...

Spotlight Projects

LID vs SWM for the Upper Thames River

Date:

February 2016

Location:

London, Ontario, Canada

Client:

Upper Thames River Conservation Authority

Consultant:

University of Western Ontario

For more information:

Visit the Upper Thames River LID page

Discussion

The new Watershed Conservation Centre (WCC) of the Upper Thames River Conservation Authority (UTRCA) is situated next to Fanshawe Reservoir on the north branch of the Thames River in the City of London, Ontario. It's important to consider the quality of the runoff discharging from the WCC site due to its proximity to the reservoir.

Low Impact Development (LID) and conventional stormwater management (SWM) were both considered for this site to minimize the effects of stormwater runoff on downstream water quality. LID techniques can minimize the effects of urban development and alleviate the pressure on a stormwater sewer system.

In fact, LIDs eliminated the use of storm sewers on this site. PCSWMM modeling techniques for various storm events and rainfall duration were used to analyze and compare the performance of the SWM LID techniques used in the two WCC parking lots to the conventional SWM techniques used.

PCSWMM analysis indicated that the LID techniques increased infiltration by approximately 64% and reduced runoff for the various storm events and durations considered in the study. The rate of peak computed runoff in the pervious parking lot was reduced by approximately 78% compared with the impervious parking lot. In addition, PCSWMM modeling results showed the time to peak was delayed in the pervious parking lot.

This project has led to a significant reduction in the amount of stormwater going into the Thames River, and has been useful in improving water quality and watershed health in the surrounding area. The insight gained by the UTRCA throughout this study is being utilized to continue enhancing solutions to infiltrate, filter, store and evaporate stormwater runoff in London, Ontario.

LID Modeling to Assess Flood Reduction in Thailand

Date:

February 2012

Location:

Bangkok, Thailand

Client:

Asian Institute of Technology

Consultants:

For more information:

Read the JWMM paper

Discussion

Bangkok’s annual monsoon cycle and flat, low-lying topography increase the likelihood of higher and longer flooding within the City. The 2011 flood was one of the largest and most catastrophic on record, impacting 2.3 million people and creating $25 billion USD in damage.

To avoid and minimize future flooding impacts and implement a sustainable approach to solving urban drainage and water quality problems in Bangkok, local urban methods were integrated with watershed-wide planning efforts.

PCSWMM was used to model single and multiple Low Impact Development (LID) technologies in a case study of the Rattanakosin village – a peri-urban community near Bangkok – as a preliminary exploration of LID benefits to stormwater quantity and quality. A 2-year design storm for Thailand was used in the modeling, and the design plans of LID technologies were visualized through PCSWMM’s support for Google Earth.

Five common types of LIDs (bioretention cells, vegetative swales, rain barrels, porous pavement and infiltration trenches) were studied. While all LID scenarios reduced Combined Sewer Overflow (CSO) volume, CSO pollutant loadings and the durations of surface flooding, the combined rain barrel and bioretention cell scenarios offered the greatest control in reducing CSO discharges.

In comparison with the current conditions, the hybrid scenario reduced CSO volume by 41% and CSO pollutant load by 34% to 40% – and surface flooding was virtually eliminated.

This project was successful in introducing students at the Asian Institute of Technology to model use, and acted as a demonstration of model utility to government personnel. Exploring various LID options throughout the study has helped to promote cost-effective applications for minimizing devastation from flooding within Thailand in the future.

Sustainable Neighbourhood Retrofit Action Plan (SNAP)

Date:

March 2010

Location:

Brampton, Ontario, Canada

Clients:

Consultant:

Computational Hydraulics Int. (CHI)

For more information:

Visit the SNAP page

Discussion

As part of an effort to prepare Brampton, Ontario's County Court neighborhood of 5,800 people for climate change and help the community become more environmentally friendly, greener streetscapes were sought.

Referred to as the Sustainable Neighbourhood Retrofit Action Plan (SNAP), this project involved using PCSWMM to evaluate a variety of Low Impact Development (LID) scenarios to determine which ones lead to the greatest improvement in stormwater quality and quantity. Flow monitoring data collected from two storm sewer locations was used for model calibration, and water quantity was continuously tracked.

PCSWMM was utilized to create the SWMM5 model as it has a number of built-in tools that assisted in project management, assembly, calibration and inference; including its physically-based LID/GI modeling approach, topological tools for fast parameterization, and the Sensitivity-based Radio Tuning Calibration (SRTC) tool that reduced the time required for calibration.

Since the completion of this project, the City of Brampton has since successfully installed its first bio-filter swale and identified a multi-objective solution, addressing irrigation and untreated stormwater.