Kohnen, Eric

Eric has 6 years of experience working as a Water Resources Engineer in Jacobs' Toronto office after completing his master's degree at Stanford University. During his time in Jacobs Eric has been involved in the conceptualization and development of both 1D and 2D hydraulic and hydrologic models for a variety of applications across Canada and globally.

Titles from this speaker

2D or Not 2D: That is the Question

Abstract

The Fairbank Silverthorn Storm Trunk Sewer System (FSSTSS) project is one of the Basement Flooding Protection Program which began in 2005 implemented by the City of Toronto. The program separates the City into study areas investigated through individual Environmental Assessments to develop 1D dual drainage models to evaluate potential flood reduction measures. Solutions identified are required to meet specified level of service criteria during the 100-year design storm event comprising a minimum freeboard of 1.8 m in storm and combined sewers and a maximum surface water depth of less than 150 mm within the road right of way (ROW) with reverse sloped driveways (RSDs) or 300 mm otherwise. The FSSTSS project focuses on reducing overland and primarily combined sewer system flooding in a dense suburban neighbourhood. The primary scope is to separate or reduce stormwater into the combined sewers and to construct a 4.5 m diameter storm storage tunnel which discharges into Black Creek. Other flood reduction measures are proposed where it was not cost effective for a direct connection to the storm tunnel, including one local storm storage facility adjacent to Woodborough Park, a small City-owned green space located within a commercial/industrial neighbourhood. Based on field observations and photographs taken during recent extreme storm events in 2018 and 2020, significant overland flooding was observed within the park causing visible damage to the local playground, and ponding depths of approximately 0.5 meters at low points within the park illustrated in Figure 1. The design developed using the 1D dual-drainage model where the overland system is represented using 1D links between nodes recommended a large underground storage facility consisting of a 190 m long 3.6 wide x 3.0 m high concrete box culvert to store about 1210 m3 of storm runoff collected via 10 high-capacity inlet (HCI) catch basins. This design alternative presented a significant constructability challenge as locating the large storage facility within the park would limit the park and baseball field use by local residents, and fitting this storage facility within the local road ROW would create substantial conflicts with other utilities and disruption along a busy road. To validate the observed flooding within the park, gain a better understanding of existing flood pathways and ponding areas, and optimize the size and location of the storage facility, it was decided that a small scale 2D surface model (39 ha) would be integrated within the existing 1D model, illustrated in Figure 2. The 2D model was completed using high resolution digital terrain model data to develop a 2D flexible mesh for the catchment area draining to Woodborough Park. The domain includes a full representation of surface roughness and a higher mesh resolution within the road ROW where most surface flow is being captured. Through the implementation of the small 2D domain it was possible to validate flooding conditions within the park using observed rainfall data and confirm primary flow paths for the storm runoff to the park. Additionally, it was confirmed that the original 1D model implicitly introduces conservatism due to the significantly faster routing time for overland flows to low points in the topography, as they do not provide sufficient resolution for capturing local depressions, flow paths, and obstacles for overland flow. This is best shown through a comparison of the hydrographs for the overland flow captured by the HCIs at the entrance to the park between the 1D and integrated 2D models shown in Figure 3. The attenuation and better routing of flows by the 2D domain enabled the design to be optimized by reducing the overall size of the underground storage and capturing storm runoff in the road ROW more effectively at locations where runoff was observed to pond and enter the park on the refined 2D domain. The additional understanding and resolution on flow path gained through the 2D model allowed the park to be utilized better for overland storage through minor topographic refinements in the park to redirect flow to the natural low point during extreme storm events thus avoid damaging to the existing playground as historically observed. Figure 4 and 5 shows the optimised solution using the integrated 2D model and the corresponding 100-year design storm performance which meets the City's freeboard and ROW overland requirements. A summary of the final design relative to the original design is provided in Table 1. This project demonstrates how innovation and digital technology advancement in modelling can be used to mitigate flood risk using real time evidence of increased storm severity and frequency in an ever-changing climate. It also demonstrates how the utilization of the latest 2D modelling technology through an additional CA$30,00 spend can support nature-based and green infrastructure solutions while providing economic savings of about CA$2.5 million. In this paper, we will discuss the approach and techniques used to integrate the 2D model with the 1D model and corresponding learnings from sensitivity analysis of various 2D modelling elements. The comparison of solutions derived using the full 1D model versus the integrated 2D and the corresponding benefits and limitations of using the two different models for solution development will allow us to conclude on that question. 2D or Not 2D?

This paper discusses the benefit of implementing a small 2D domain within an existing 1D dual drainage model to optimize the size of a proposed storage facility and reduce overland flooding in a dense suburban neighborhood in the City of Toronto. This paper documents the approach used to optimize the solution using a combination of green and grey infrastructure, including a comparison of the 1D vs. 2D solutions as well as conclusions and limitations of this approach identified during deisgn.

SpeakerKohnen, Eric

Presentation time

08:30:00

08:45:00

Session time

08:30:00

10:00:00

SessionPlanning Techniques to Support I/I Mitigation, Master Plans and Design

Session number302

Session locationRoom 356

TopicAsset Management, Collection Systems, CSO & SSO Planning and Mitigation, Intermediate Level

Author(s)

Kohnen, Eric, Hon, Amanda, Santaella, Ricardo, Li, Allen

Author(s)E. Kohnen1, A. Hon1, R.A. Santaella2, A. Li3

Author affiliation(s)1Jacobs, ON, 1, 2Jacobs Engineering, Ontario, 3City of Toronto

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159640

Volume / Issue

Content sourceWEFTEC

Word count9

Peterborough Integrated Flood Model: A Comprehensive Approach to Managing Flood Risk

Abstract

This presentation will highlight the development of an Integrated Flood Model (IFM) for the City of Peterborough, Ontario. The City-wide IFM was built in MIKE+ and divided into 5 models which include 350 km of storm sewers, 41 km of 1D riverine system, 40 storm water management ponds, and approximately 55 km2 of two-dimensional mesh to represent the existing terrain. The fully dynamic 1D/2D IFM model provides the City with an effective tool to assess, forecast, plan, and mitigate against the risk of urban and riverine flooding events. This tool will act as a data-driven and evidence-based tool to support the City's decision-making, planning and prioritizing of future flood mitigation projects, and to inform asset management efforts for both existing and future conditions. The impetus for this project was a severe urban storm in the City of Peterborough in 2004, which resulted in over $100M in damages, and the likelihood of hybrid (urban-riverine) flooding due to the rivers traversing the city and increasing urbanization. To address the City's resilience to flooding events, a cross-collaborative effort was undertaken to develop performance scenarios including the City's planned growth and urbanization, climate change forecasts, and evaluate the impact (positive or negative) of adding the City's planned flood reduction and Low Impact Development (LID) projects. This process involved the complete model build-out using GIS information provided by the City and discretizing of the model's catchments to a catch basin level. Additionally, the project used master plan information to identify locations of planned City expansion and densification to develop a high-level schematization to evaluate potential impacts to the existing collection system and watercourses. The model also included a high level representation of LIDs to assess its impact in terms of both flood mitigation through attenuation of overland flows, and potential water quality benefits through increased infiltration potential. The approach used to develop the IFM was selected to provide a balance between providing a high level of detail and minimizing simulation run times. For example, rather than providing a fully 'rain-on-grid' schematization, a hybrid approach was selected by using delineated subcatchments to perform the hydrologic simulation which are coupled to the two-dimensional mesh via one dimensional elements. This approach allows for entirely 1D simulations to be performed for smaller storm events where it is safe to assume the collection system will capture a majority of runoff. Additionally, since rain on grid simulation by nature will activate the entire two dimensional mesh during simulations, the level of refinement that is required to avoid localized areas causing a model instability can be significant. Particularly in the case of the IFM where schedule was a major driver for the approach for the model build, using a hybrid approach can greatly reduce troubleshooting while performing simulation of larger storm events. A full suite of storm events was used to evaluate each performance scenario to help identify flood risk associated with both volume- (historical) and intensity- (design storms) based events. Intensity, Duration and Frequency (IDF) Curves were adjusted using the tool developed by the Institute of Catastrophic Loss Reduction (ICLR) and Western University to calculate projected rainfall intensity which incorporates the effects of climate change. An IFM model of this scale generates multitudes of data that must be post-processed to create the tools and products to support the City's decision making. To effectively communicate and illustrate results and analyses, an innovative approach was required to compile GIS data into a single geodatabase and automate the processing of model results. The IFM results were used to facilitate a comprehensive GIS analysis for each scenario to evaluate a variety of different metrics related to the extent and severity of flooding for the entire city, which included the number of impacted 'critical' sites and buildings, deficiencies in the storm sewer system, and locations of excessive overland flooding. Dynamic flood maps and dashboards were also developed using ArcGIS Online to give the City the ability to review, compare and/or share results with stakeholders for each performance scenario effectively, considering the large scale of the project. Training sessions with City staff on how to operate, modify and maintain the completed models as well as the master GIS database were also completed to ensure that the integrated flood model will be a useful tool for this City in the years to come.

This presentation will highlight an Integrated Flood Model (IFM) for the City of Peterborough, Ontario. The City-wide model includes the storm sewers, riverine system, 2D overland mesh, and provides the City with an effective tool to assess, forecast, plan, and mitigate against the risk of urban and riverine flooding events. T he IFM generates multitudes of data that must be post-processed to create a GIS portal to effectively communicate results and spatial analyses.

SpeakerSantaella, Ricardo

Presentation time

15:30:00

16:00:00

Session time

15:30:00

17:00:00

SessionModeling for Inland Flood Resilience

Session number429

Session locationRoom 350

TopicIntermediate Level, Resilience, Safety, and Disaster Planning, Stormwater and Green Infrastructure, Sustainability and Climate Change, Watershed Management, Water Quality, and Groundwater

Author(s)