Urban Flood Mitigation and Stormwater Management

James C Y Guo

• Publisher: CRC Press
• Year: 2017
• Print ISBN: 9781138198142
• eBook ISBN: 9781351980494
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

Effective urban drainage to manage stormwater and control flooding depends on good engineering, especially when an environmentally sustainable approach is being applied. This new text focuses on green methods and modelling techniques. It covers the principles of hydrology and drainage, low-impact-development (LID) designs, computer modelling techniques, the evaluation of existing systems, and planning for both new development and urban renewal. It outlines design procedures using examples, spreadsheet models, photos, and real-world design examples.

Unlike other books, which focus on extreme events, this book covers hydrologic designs for both extreme and frequent events, and reflects the latest revolution in stormwater LID management, and takes a quantitative as well as a qualitative approach.

PowerPoint® presentations and Excel® computer models are provided to follow and build on the exercises in the book. It is written especially for students on urban watershed courses, and also for those studying urban planning, landscaping, water resources, hydrology and hydraulics.

Chapter 1

Urban stormwater planning

One of the major tasks in urban development is to provide adequate stormwater drainage systems to preserve the water environment and to promote the public health and economic well-being of the region. Driven by the gravity, stormwater does not follow any man-made jurisdictional boundaries and regulations of water rights as it flows through depressions, gullies, and washes, seeking an ultimate terminus such as rivers, lakes, or oceans. An engineered design is an attempt to control the drainage of stormwater while at the same time maintaining the integrity of natural flow paths and existing legal and liability relationships arising from land ownerships. It takes a joint effort to achieve such a goal, starting from the local and heading to the regional. Stormwater planning for a region can affect all governmental jurisdictions and all parcels of property in the watershed. The major characteristics of stormwater require coordination among all entities involved and cooperation from both the public and the private sectors. Regional Master Drainage Planning (RMDP) is an approach that integrates both local and regional efforts to identify drainage conveyance and storage facilities based on hydrological optimization and cost minimization individually and collectively.

1.1 Drainage plan

An RMDP incorporates, insofar as possible, planning completed or undertaken by the local government or land developers. It sets forth the most currently effective structural and regulatory means for improving the existing flooding conditions within an area, taking into account the possible effects under future development conditions. An RMDP shall provide basic drainage information including

1. Locations of regional drainage facilities
2. Inflow and outflow information at all design points
3. Flooding problems and future improvements
4. Estimated costs for various alternatives

An RMDP can be modified and/or revised from time to time to reflect the changes desired by the local entities as long as the intent and integrity of the RMDP are not compromised.

Under the guidance of an RMDP, a set of Local Drainage Plans (LDPs) can be developed as elements to the RMDP required to preserve and to promote the general health, welfare, and economic well-being of the area. An LDP sets forth the site requirements for new developments and identifies the required local public improvements. All local flood mitigation facilities must be designed in a manner to collectively achieve the regional goals stated in the RMDP. If a local flood mitigation facility impacts other entities and/or regional flood-control facilities, then the local drainage planning must be coordinated with the affected entities.

When planning urban drainage facilities, certain underlying principles and design criteria provide directions for this effort. These principles are made operational through a set of policy statements stated in the local stormwater and urban drainage design criteria. The design criteria are developed with the support of local field data and facilitated by technical reviews, permitting approvals and construction inspections for all proposed designs and constructions within the watershed. Using a comprehensive approach by involving public and private sectors, all local and regional drainage facilities are provided as the watershed is being developed in such a manner that the entire watershed is protected from the preselected flood risk.

1.2 Doctrines for surface water drainage

Under the common enemy rule, all property owners may protect themselves from flood water, but they cannot make flood water more dangerous to their neighbors. Basically, the rule includes the concepts as follows:

1. Drainage problems should not be transferred from one location to another.
2. An upstream landowner can request a drainage easement over the downstream properties, but shall not unreasonably burden the downstream properties with increased flow rates or unreasonable changes to the natural waterway from upstream properties.
3. The downstream properties cannot block natural runoff through their site and must accept runoff from upstream properties.

In an urban area, the development process alters the historic or natural drainage paths and sets the possibilities to violate the aforementioned regulations. As a result, strict compliance with the abovementioned rules can produce drainage systems that become impractical or very costly to the general public. Therefore, the concept of Reasonable Use of Drainage was developed to design economic and efficient drainage systems within the limits of drainage laws. The concept of Reasonable Use of Drainage is defined for planning purposes to provide an economically and hydraulically efficient drainage system that is demonstrated by not adversely affecting downstream properties. Under the concept of Reasonable Use of Drainage, new developments are allowed to occur while preserving the rights of adjacent property owners. A stormwater drainage system is an integral part of the total urbanization process. The RMDP shall be included in the regional and local land use plans with the following considerations:

1. Multiple purpose land uses
   Drainage systems require space to accommodate their conveyance and storage functions. When the space requirements are considered, the provision for adequate drainage becomes a competing use for space along with other land uses. If adequate provision is not made in a land use plan for the drainage requirements, stormwater runoff will conflict with other land uses and may result in water damage and may impair or even disrupt the functioning of other urban systems. Therefore, often a stormwater detention system is designed with public access for picnic or sports.
2. Multiple purpose resources
   Stormwater runoff is a resource that has the potential of being utilized for different beneficial uses. These uses, however, must be compatible with adjacent land uses and applicable water laws.
3. Water rights
   A drainage design must be planned and constructed taking into consideration the existing water rights and applicable water laws. When the drainage system interferes with existing water rights, the value and use of the water rights are affected.
4. Jurisdictional cooperation
   Because drainage considerations and problems are regional in nature and do not respect jurisdictional boundaries, drainage planning must emphasize regional jurisdictional cooperation, unified standards, and similar drainage requirements in accomplishing the goals.

1.3 Design risk and consistency

The risk-based approach applies to the selection of design storm events, based on public perception, federal regulations, watershed physical characteristics, economics, and safety. Typically, the public perceives three types o...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Preface
• Acknowledgments
• Author
• 1 Urban stormwater planning
• 2 Rainfall analysis
• 3 Watershed hydrology
• 4 Hydrologic frequency analysis
• 5 Rational method
• 6 Watershed modeling
• 7 Flood channel design
• 8 High-gradient concrete channel
• 9 Street hydraulic capacity
• 10 Street inlet hydraulics
• 11 Culvert hydraulics
• 12 Storm sewer system design
• 13 Detention basin design
• 14 Flow diversion
• 15 Grate and rack hydraulics
• 16 Stormwater quality capture volume
• 17 Low-impact development facilities
• 18 Design of infiltration basin
• 19 Hydraulic routing
• 20 Hydrologic routing
• Index