Dual Drainage System Design

Design, model and analyze dual drainage systems for flood control in new, existing or combined developments. Surface flows routed overland (major systems such as roads, swales, street sags, storage areas) can easily and accurately be combined with underground flows (minor system, such as sewer infrastructure).

PCSWMM provides innovative tools for fast, accurate major/minor system modeling, analysis and design. This means that the program can be used for the design and analysis of (i) new, (ii) existing and (iii) combined new and old, urban drainage systems where surface flows are routed over the land surface (major system, such as roads, swales, street sags and storage areas) while part of the runoff simultaneously flows in the underground conveyances (minor system, such as sewer pipes and associated infrastructure). Our users tell us that the PCSWMM dual drainage tools are incredibly easy-to-use, almost too much so. The tools automatically dovetail with any or all SWMM5 engines, and with an extraordinarily wide array of established, included design storms (from 1:100 and larger to 1:1 and smaller) and long-term continuous rain data. Especially useful is the ability to simultaneously plot on one or more screens the longitudinal profile and dynamic energy and hydraulic grade profiles for all parts of the dual drainage system.

Unlimited network sizes and unlimited time steps are allowed, and the dual drainage systems need not be parallel (they may flow in arbitrary directions). Unlimited numbers and sizes of control devices and storages are allowed on both systems. Sensitivity, optimization/calibration and error analysis tools are provided for optimal design. Time-steps are semi-infinitely variable, and the usual infiltration and runoff-generating options, such as triangular unit hydrographs, are optionally available. The program will also automatically determine the minimum conveyance sizes required, including estimation of required minimum storage.

If your application includes simultaneous surface ponding, street flooding and surcharged pipes, you should step up to dynamic analysis of dual systems, with dynamic wave routing allowing for flexible inlet control, catchbasin flooding and reverse flow, street/gutter flow and overland routing, accurate surcharge and pressure flow pipe modeling, inlet/outlet controls, flooded and ponded areas, trap-lows, and much more.

Automate the creation of your major system with the Dual Drainage Creator
Easily develop detailed street cross-sections with the Street Designer
Efficiently assign inlet control (based on rating curves or capacity) for individual catchbasins or aggregated inlets
Automatically adjust junction inverts to meet minimum slope criteria
Accurately model manhole drops and account for varying energy losses at junctions
Assess the impact of multiple Low Impact Development (LID) practices
Create design storms for both major and minor events with the comprehensive storm distribution library in the Design Storm Creator tool, including standard SCS, Huff, AES, Chicago, etc. as well as locally-required design storm distributions
Automatically size pipes based on computed peak flows
Quickly tweak and test design parameters (diameters, inverts, etc.) directly in the profile view for computed HGL
Easily check for design criteria such as depth of cover, minimum slope, etc.
Perform long term, continuous modeling verification of dual drainage performance
Compare design alternatives with comprehensive scenario analysis graphs, profiles and reports

Spotlight Projects

City of Guelph Dual Drainage Reconstruction

Date:

January 2018

Location:

Guelph, Ontario, Canada

Client:

City of Guelph

Consultant:

Wood Environment & Infrastructure Solutions

For more information:

Read the JWMM paper

Discussion

Challenged with aging infrastructure, the City of Guelph retained Amec Foster Wheeler for the reconstruction of a section of roadway. The roadway is located in an older area of the city, close to the downtown core. As a result, no environmental approvals existed for the existing sub-surface utilities, and no stormwater quantity or quality measures were in place. This section of the system was serviced by small diameter storm sewers which discharged to the Eramosa River. The proposed re-construction was to include a revised surface layout, which provided dedicated bike lanes and on-street parking areas.

PCSWMM was used to develop the dual drainage hydrologic/hydraulic models for both pre-construction and post-construction conditions. The models were used to assess expected changes in flows and performance of both the major and minor drainage systems. The PCSWMM model was used to verify the proposed design and develop a stormwater management strategy.

Previous work completed in 2012 by Amec Foster Wheeler involved the use of PCSWMM for developing a Stormwater Management Master Plan (SWMP) for the City of Guelph including the creation of both storm sewer and dual drainage models for a total of 59 different sewersheds. This previous work was useful for the development of the 2016 model which includes 22 subcatchments in a 14-hectare (35 acre) drainage area and uses the Green-Ampt method for the simulation of infiltration, consistent with the approach used for the SWMP. In total, the model is comprised of 66 conduits, which includes both minor (storm sewer) and major (roadway) links. This dual drainage model also included detailed catchbasin and inlet restriction modeling for the major-minor system connections.

Following the approval of the stormwater management strategy and associated PCSWMM models, the roadway was successfully reconstructed over the course of July 2016 to June 2017.

eQuinelle Golf Course Subdivision Master Plan

Date:

January 1990 - Ongoing

Location:

Kemptville, Ontario, Canada

Client:

The Regional Group

Consultant:

Novatech Engineers, Planners and Landscape Architects

Discussion

Kemptville’s eQuinelle Golf Course features a number of interconnected ponds that serve as irrigation reservoirs and stormwater management facilities. The facilities (or wet ponds) were designed to provide water quality and quantity control for the surrounding residential community.

EPA SWMM was initially used to develop the master drainage plan, and because of PCSWMM’s advanced functionality (GIS integration, easy-to-use GUI, etc.) the software is now being used to design and evaluate the stormwater management strategy for future phases of development within the community. For this project, the pipe network (minor system) and ground surface (major system) were created in Autodesk Civil 3D.

The pipe network was then imported into Autodesk Storm and Sanitary Analysis (SSA) as a LandXML file, exported as a EPA SWMM 5.x file, and imported into PCSWMM. The road network was imported into PCSWMM by creating cross-sections (transects) in Autodesk Civil 3D, exporting them to HEC-RAS and then importing the HEC-RAS model into PCSWMM.

Due to the size and complexity of the development, it would be very time-consuming to manually input and update all the information in the model to reflect ongoing changes to the design. As such, it was important to develop a methodology for creating and updating the model while maintaining georeferencing and accuracy.

The methodology developed provides a time- and cost-saving approach to creating and updating existing and proposed PCSWMM models. Using PCSWMM and the GIS capabilities it provides also helps the approval agencies with their modeling reviews - reducing the amount of comments that originate from misinterpretations.

Residential Subdivision Flood Control in Ottawa, Ontario

Date:

January 2013 - July 2016

Location:

Stittsville (Ottawa), Ontario, Canada

Clients:

Consultant:

Novatech Engineers, Planners and Landscape Architects

Discussion

The upstream development of Area 6 – an existing residential subdivision located within Ottawa, Ontario in Stittsville’s South End – recently had inlet control devices installed in the catchbasins in order to restrict the flow from getting into the storm sewer system. As a means of analyzing the overland flow depths and velocities of the major system flow through the subdivision, a 2D PCSWMM model was developed.

It was important that the major system be safely conveyed overland to the nearby watercourse, Faulkner Drain. Inevitably, this led to increased discharge into the neighbouring properties that were slated for development in Area 6.

Autodesk Civil 3D was used to complete the grading design for the proposed subdivision, and the proposed ground surface was exported as a Digital Elevation Model (DEM) for input into PCSWMM. The final grading design showed that the major system flow can be safely conveyed from the discharge point upstream the site, through the site and to the outlet.

The resulting 2D model was based on the DEM, and the major system hydrograph (provided by the City of Ottawa) was inputted into the model. Indicating spill areas where the grading design needs updating, the 2D model helps to ensure that the surface is upgraded so the major system can be safely contained/conveyed to the Faulkner Drain.

Integrated Dual Drainage Model for the City of Ottawa

Date:

2015

Location:

Ottawa, Ontario, Canada

Client:

City of Ottawa

Consultant:

Parsons

For more information:

Read the ICWMM abstract

Discussion

Faced with the risk of surcharging and surface flooding, the City of Ottawa conducted an Integrated Dual Drainage Study. The study supports city-wide comprehensive asset and wet weather infrastructure management plans by characterizing existing drainage conditions, identifying existing levels of service and defining constraints and opportunities within the study area.

PCSWMM was used to develop and evaluate a pipe-by-pipe model, and GIS and spreadsheet analysis were used to prepare input data, perform complex analyses and render results. Sewer hydraulic grade line and percent pipe full capacity were used to characterize the minor system performance. Major system classification was based on ponding depths/extents, conveyance system, private property crossing points and level of service within Collector roads.

Input rainfall was based on the City’s design storms (various return periods), while impacts of climate change were simulated by increasing storm intensities by 20%. To qualitatively validate the PCSWMM model, simulations of historical storms were run and the results were tested against flooding reports documented by the City.

The results indicated the minor and major systems had average levels of service of 1:5 and 1:100 years, respectively. A systematic approach was used to evaluate various alternatives to improve system performance, starting with those most basic and cost-effective and then gradually increasing the cost and complexity until the desired balance was achieved.

By restricting flows to the minor system with inlet control devices, average inlet capture rates could be reduced by 40 - 70%, significantly reducing the risk of sewer surcharging conditions during a 1:100-year storm. Reduced inlet capture translated into increases in surface flows and ponding duration, although these were effectively accommodated within the existing capacity of the major system.

Cooksville Creek Dual Drainage Model

Date:

June 2014

Location:

Mississauga, Ontario, Canada

Clients:

Consultant:

Computational Hydraulics Int. (CHI)

For more information:

Read the ICWMM abstract

Discussion

Located entirely within the City of Mississauga, the Cooksville Creek watershed has been under increasing urban development pressure since the 1940’s and has experienced flooding during recent large storms.

In response, working closely with the Credit Valley Conservation Authority and the City of Mississauga, CHI developed a detailed hydrologic/hydraulic dual drainage (i.e. minor/major system) model for the watershed using PCSWMM.

The objective was to determine overland flow routes (major system), hydraulic grade lines and the capacity of existing storm sewers (minor system), as well as to assist with master planning and historical event analysis.

PCSWMM was utilized because of its ability to efficiently process and calibrate the highly detailed 33 km² dual-drainage watershed model, which included more than 4,000 subcatchments, 8,000 conduits and 500 km of drainage network.

Model calibration success was measured using Nash–Sutcliffe efficiency coefficient for maximum and total event flows, indicating a very good calibration at the flow gauge location. The model continues to be instrumental in helping the City of Mississauga understand the effect of drainage infrastructure improvements on reducing the extent and frequency of flooding.