Session 05B: Stormwater
1:15pm - 2:00pm
Characterization and Application of Hydraulic Modeling to Assess Instream Enhancement
Clean Water Services, United States of America;
The Oregon Department of Environmental Quality (DEQ) implements the stormwater management programs under a permit officially known as “Phase I National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) Discharge Permit”. Reducing or eliminating the impact of hydromodification on natural stream functions has become a stormwater permit condition for Oregon MS4 Phase 1 permittees. In general, permittees must promote infiltration of stormwater to alleviate hydromodification effects in nearby water bodies, such as increased water volume and increased water velocity in streams neighboring urbanized (or in development) areas. Some of the common detention facilities such as ponds, tanks and vaults are not suitable to achieve the proposed MS4 measured because there is not available space to allow their construction and development. For these scenarios, Clean Water Services (CWS) have considered the enhancement of stream corridors in lieu of detention facilities. This approach allows repairing degraded channels by reducing the velocity to which surface runoff reaches the main stream, allowing a reduction of the local and system-wide velocity, reducing erosion of channel beds and banks and allowing infiltration on designated flood plains. CWS have designed several project sites and designated them as informal field “laboratories” to test and evaluate the effectiveness of this approach. Stream corridor enhancement is made up of several components and instream features (such as large wood structures) is one of them. Commonly, the instream features require design analysis in urban streams to manage the potential for conflicts with existing infrastructure. Due to the complexity of these systems, modeling their effects on flow, velocity and stream depth is challenging. The proper characterization and simulation of instream features is very valuable, because we can estimate and quantify the interactions of a series of them, facilitating their design and the understanding of their field effectiveness. In this work, we present a series of three different techniques that support the simulation of the instream structures using a 2D model for one of our informal field laboratories. Our goal is to be able to demonstrate differences between the techniques and select that one that may represent better the instream structures.
2:00pm - 2:45pm
Rapid and Efficient Modeling of Citywide Urban Flooding for Extreme Storms
Brown and Caldwell, United States of America;
As the magnitude and frequency of extreme storms increase, cities seek to understand the potential risks and possible impacts of a large and intense rainfall event. This type of extreme event produces runoff that far exceeds the design capacity of combined sewers and drainage systems, which generally results in multidirectional surface flows and flow paths are not readily apparent. Coupled 1-dimensional/2-dimensional modeling can simulate extreme flooding conditions in urban settings; however, the time and effort required to do so at a city scale is often impractical. This presentation will discuss a rapid and efficient approach to urban flood modeling implemented by Seattle Public Utilities (SPU) as part of the utility’s long-range planning to improve the resilience of local communities. The modeling approach reduces the problem to focus on surface flows and simplifies the 2-dimensional computations using the CADDIES tools developed by the University of Exeter. In addition, simulations were accelerated using parallel processing run through cloud computing resources. As a result of this work, SPU has prepared citywide flood risk area mapping and established a better understanding of the community’s vulnerable areas.