Stormwater Design Manual Executive Summary

Chapter 1. Design Manual Overview

This chapter serves as an executive summary of the design manual. It summarizes the manual’s purpose, background, goals and provides chapter descriptions. It also provides information about additional permitting issues related to the construction of stormwater management facilities beyond the requirements of the County.

Chapter 2. Stormwater Plan and Permit Requirements

This chapter provides an overview of the various development processes and the required information for plan and permit submittals. This includes the expectations for each type of plan sheet or calculation Boone County Road & Bridge requires for the approval of stormwater management facilities and associated pollution prevention in subdivisions, planned developments and commercial site development. Plan review checklists corresponding to these requirements can be found in Appendix B.

Chapter 3. Hydrology and Hydraulics

This chapter provides a brief review of the hydrologic and hydraulic calculations and formulas for determining runoff quantities, velocities and system capacities. This chapter is not intended as a substitute for formal hydrology and hydraulics training and may also be supplemented by extensive information available in industry accepted computer software for hydrologic and hydraulic modeling. Various charts and figures to assist with these calculations are included at the end of the chapter (Chapter tables and figures).

Information on determining water quality and channel protection volumes is also included in this chapter. However, specific design guidance for sizing individual post-construction best management practices can be found in the Mid-America Regional Council’s (MARC) Manual for Best Management Practices for Stormwater Quality dated March 2008.

Chapter 4. Enclosed Systems

This chapter provides specific design criteria for the locations and sizing of storm sewer systems. This includes protection from flooding for various classifications of streets. Energy dissipation at the outlet of an enclosed system is discussed both here and in Chapter 8 – Erosion and Sediment Control. The chapter also includes guidance for reviewing the overflow from the enclosed system. Various charts and figures to assist with these calculations are included at the end of the chapter.

Chapter 5. Open Channels

This chapter provides guidance in natural stream protection and design criteria for the locations and sizing of engineered open channel stormwater conveyance systems. Natural stream protection is partially addressed in the zoning code through the stream buffer regulations. However, it is recognized that occasionally it is necessary to enter the streamside zone or the stream for utility and road crossings. This chapter provides guidance for limited stream assessments to minimize the impacts of the construction activities and the location of stormwater outfalls. Various charts and figures to assist with these calculations are included at the end of the chapter.

Chapter 6. Stormwater Management

The traditional stormwater management goals for quantity management have centered on storing peak volumes of runoff from large rainfall events and discharging it at a slower (typically pre-development) rate. While traditional storage practices can reduce the peak runoff flows from urban development and provide some level of flood protection, the increase in runoff volume and frequency of peak flows is not reduced and very little improvement in stormwater quality is accomplished unless the water is retained in the basin for more than six (6) months. This chapter provides design criteria for the design of facilities to address quantity management. Design methodologies for sizing these facilities may be supplemented by Hydrologic and Hydraulic information found in Chapter 3. This chapter also discusses a wider variety of alternatives to traditional pond storage. Discussion of operation and maintenance plans is also presented.

Although management of the quantity of stormwater runoff reduces impacts to natural channel systems, it does not sufficiently address treatment of pollutants introduced in the developed environment. This chapter further discusses typical pollutants generated by different types of land treatments and the BMPs that can address these pollutants. Stormwater management plans, as required by the Stormwater Management Ordinance, will address both the quantity and quality of the stormwater runoff from developments.

Chapter 7. Protection of Environmentally Sensitive Areas

This chapter highlights the additional issues presented by the development of land near environmentally sensitive areas such as Karst sinkholes, caves, springs, losing streams, wetlands, and outstanding state resource waters. Per the Stormwater Management Ordinance, developments near these areas will require additional measures be taken to reduce the risk of any surface or groundwater contamination. Additional information related to the identification of these areas is provided in Appendix C.

Chapter 8. Erosion and Sediment Control

This chapter provides a menu of various construction site related best management practices for erosion control, stormwater runoff management, sediment control, tracking control and general good housekeeping for pollution prevention. Both the erosion and sediment control plan sheets and narrative (Stormwater Pollution Prevention Plan – SWPPP) should utilize options within this chapter to describe how the contractor will attempt to prevent the discharge of pollutants during construction activities.

As noted in this chapter, this is not intended as an exhaustive list of BMPs and specifically did not attempt to address the growing variety of proprietary products on the market for these purposes. The County encourages the introduction of various alternatives to the plans if the ultimate objective of pollution prevention can be achieved.

This chapter is significantly based on guidance developed by the City of Springfield. We appreciate their sharing of their draft erosion prevention and sediment control guidelines.

Appendix A. Definitions

Occasionally the vernacular used to describe land development planning and zoning issues does not correlate with the combined stormwater quality and quantity goals set forth in this manual. This appendix provides definitions to better serve the user of this manual.

Appendix B. Checklists and Worksheets

This appendix provides the user copies of the plan review checklists that will be utilized in the review and approval of all plans and reports required by the Stormwater Management Ordinance and further detailed within this manual. It is recommended that the developer’s engineers utilize these checklists to minimize the comments received from staff and expedite the approval and permitting process. These checklists correspond to plan requirements in Chapter 2. Worksheets have also been designed to aid with understanding and concept clarification. Several of the workshops are mandatory, and will help speed the plan approval process.

Appendix C. Environmentally Sensitive Areas

This appendix provides a list of specific environmentally sensitive areas as identified in the Code of State Regulations. This information may be supplemented by GIS databases.