With the continued need to protect human life, property, and natural resources, development projects in Texas need to change how storm water is integrated into the planning and design process. The predominant approach to storm water management in North Texas has been quantity based to address peak runoff from new development. Storm water regulations, quality of life issues, and environmental stewardship are driving municipalities and other entities to use better practices for management of storm water.
In simple terms, iSWM™ is a new way of managing storm water in North Central Texas. The iSWM™ program is intended to help communities within NCTCOG’s planning region move toward a comprehensive approach to storm water management planning and design that integrates storm water quantity and quality objectives. The goal of iSWM™ is to develop an effective methodology for storm water management that provides consistency and uniformity across jurisdictional boundaries. This goal complements NCTCOG’s vision to provide sustainable environmental excellence through water resources and green space planning which will create safe, clean and green regional environmental corridors.
The three fundamental objectives of the iSWM™ management approach are to address storm water quality, streambank protection, and flood control in an integrated approach through the planning and design of a project. By implementing a development process that places an emphasis on storm water at the earliest phases of development, the three fundamental goals can be addressed in an integrated approach. This paper will focus on the iSWM™ Site Plan, the iSWM™ Development Process, and the iSWM™ Planning and Design Approach. The iSWM™ Site Plan includes the use of the integrated Site Design Practices and integrated Storm Water Controls being recommended for North Texas. This paper discusses the core of the iSWM™ Design Manual for Site Development that has been released in North Texas, effective March 2006.
The integrated Storm Water Management (iSWM ™tm) program has been developed by the North Central Texas Council of Governments (NCTCOG) to provide guidance for all development and redevelopment related storm water initiatives in North Central Texas. A consultant team led by Freese and Nichols, Inc. is developing the program, funded by 55 municipalities in 9 counties of the North Texas region. The 2006 Edition of the iSWM ™ Design Manual for Site Development has been used as the basis for this paper. (available at http://iswm.nctcog.org)
The three fundamental goals of storm water quality, streambank protection and flood control are proposed to address the negative impacts of development. This is accomplished by integrating the management of storm water quality and quantity into the earliest stages of the development and site planning process. The benefits of an integrated approach include minimized flood risks and pollution of water resources, protection of natural drainage systems, and an alternative to End-of-Pipe treatment.
Purpose of iSWM ™
In order to effectively and efficiently manage storm water on new development and redevelopment sites, consideration of storm water runoff needs to be fully integrated into the site planning and design process. This involves a more comprehensive approach to site planning and a thorough understanding of the physical characteristics and natural resources of the site. In addition, the management of the quantity and the quality of storm water should be addressed in an integrated approach. The purpose of iSWM ™ is to provide design guidance and a framework for incorporating effective and environmentally sensitive storm water management into the site development process, and to encourage a greater uniformity in developing plans for storm water management systems that meet the following goals:
- Control conveyance of runoff within and from the site to minimize flood risk to people and properties;
- Regulate discharge from the site to minimize downstream bank and channel erosion; and
- Reduce pollutants in storm water runoff to protect water quality;
When designing the storm water management system for a site, a number of questions need to be answered by the site planners and design engineers, including:
- How can the storm water management system be designed to address most effectively the quality of runoff from the site, protect against increased streambank erosion, and meet flood control objectives?
- What are the opportunities for utilizing site design practices to minimize the need for and the size of structural storm water controls?
- What are the development site constraints that preclude the use of certain structural controls?
- What structural controls are most suitable and cost-effective for the site?