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MWH Soft Enhances SSO Communities with New Tool for State-of-the-Art Rainfall Dependent Inflow and Infiltration Planning and Analysis


Revolutionary RDII Analyst Extension Addresses Critical Wastewater
Utilities’ Need to Mitigate Pollution from SSOs

Broomfield, Colorado USA, April 2008 — MWH Soft, a leading global provider of environmental and water resources applications software, once again moved the wastewater industry to the head of the line for key new modeling capabilities with the release of RDII Analyst Extension for InfoSWMM and H2OMAP SWMM executive suites. The new extension offers invaluable risk management capabilities for planning and designing high-cost Sanitary Sewer Overflow (SSO) control.

RDII Analyst directly addresses industry challenges to develop sound capital improvement programs and the need for SSO mitigation plans that safeguard against hazards and limit liabilities by greatly accelerating accurate analysis of sanitary sewer systems capacity and helping to ensure reliable and effective SSO control plans. The introduction sets new benchmarks in sanitary sewer overflow analysis, planning and management.

Excessive Rainfall Dependent Inflow and Infiltration (RDII) can reduce sanitary sewer carrying capacity, causing sewer surcharge and overflows to basements, streets, or nearby streams. It can also cause serious operational problems at wastewater treatment plants. Together, the nation’s 19,500+ sanitary sewer collection systems, serving an estimated 150 million people, report about 40,000 SSO events each year.

The ability to accurately predict RDII flows is critical to performing sound capacity analysis of sanitary sewer systems and determining effective and economical remedial measures. The industry standard and most accurate RDII prediction method is the USEPA RTK synthetic unit hydrograph. This method uses up to three triangular unit hydrographs to estimate fast, medium, and slow RDII responses. The R parameter is the fraction of rainfall volume entering the sewer system as RDII, T is the time to peak, and K is the ratio of time of recession to T.

These parameters are normally computed through a tedious and inexact trial-and-error process in which they are adjusted to closely match wet-weather flow data. Since there are a vast number of possible combinations of RTK values, evaluating all options this way is unfeasible, and even knowledgeable modelers often fail to obtain good results. As the size of the sewer system and number of flow datasets increase, the trial-and-error approach may not be effective or reliable, or even manageable — especially with the added factor of time and cost constraints. The result is inefficient performance at a greater cost.

The new RDII Analyst extension greatly improves the reliability of RDII flow prediction and eliminates the need for trial-and-error parameter estimations. The program performs rigorous QA/QC of rainfall and meter data and decomposes flow data into dry-weather flow (DWF) and wet-weather flow (RDII) components. The DWF component is further analyzed to construct a DWF pattern. This pattern is then assigned to the source nodes that contribute flow to the meter location, proportional to sewershed areas or based on any other user-defined criteria.

Using advanced Genetic Algorithm optimization, RDII Analyst then quickly and automatically determines the RTK parameters that best match the RDII time series generated by decomposing the measured flow data. The resulting inflow hydrograph (RDII + DWF) is then used by InfoSWMM or H2OMAP SWMM to carry out detailed dynamic flow routing through the sewer system and evaluate system response to support development of an optimal capital improvement program.

Powerful, comprehensive and engineer-friendly, RDII Analyst reflects MWH Soft’s time-honored practice of continually adding value to its world-class software and bringing critical new design and optimization capabilities to the wastewater industry. It allows engineering professionals to quickly and efficiently complete complex SSO projects and develop sound mitigation plans. The program’s intuitive interface, easy-to-use functionality and rich graphing and reporting capabilities save modelers hours, if not days, of manual calculation time, making it simple to predict, analyze and optimize RDII flows for capacity analysis and SSO planning.

“The operational simplicity, power, speed and flexibility of RDII Analyst eliminate the obstacles that make RDII planning and analysis overly complicated and inefficient,” commented Paul F. Boulos, Ph.D, President and COO of MWH Soft. “Civil and environmental engineers’ SSO projects are very complex, but their tools shouldn’t be. These professionals have long needed a versatile, engineer-friendly product that can quickly and accurately predict RDII flows and speed up project completion, and that’s exactly what RDII Analyst gives them. The software’s comprehensive capabilities will greatly assist wastewater modelers in making informed decisions that ensure optimal sewer system performance. With this introduction, we now offer the best in sanitary sewer collection system modeling and design, integrated with the best in engineering.”

Pricing and Availability
RDII Analyst is now available worldwide by subscription to the InfoSWMM or H2OMAP SWMM Executive Program. Subscription members can immediately download RDII Analyst free of charge directly from For the latest information on the MWH Soft Subscription Program, including availability and purchase requirements, visit or contact your local MWH Soft Certified Representative.


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