Erie County Engineer's Office

Storm Water Rules and Regulations (SWRR)
Version: December, 1994

Chapter Two

Stormwater Runoff Control

Section 2.00 Purpose

Stormwater Management Rules and Regulations have been adopted for the
purpose of regulation non-farm, earth-disturbing activities to control sediment
pollution caused by accelerated soil erosion. Stormwater management is premised on the fact that non-farm, earth-disturbing activities which increase the rate and/or volume of runoff will also increase the rate of erosion and volume of sedimentation. Therefore, earth-disturbing activities which increase the rate and/or volume of runoff shall be required to control the discharge rate of runoff prior to its release to off-site land. The purpose of controlling the release rate is as follows:
1. Permit development without increasing the flooding of the lands.
2. Reduce damage to receiving streams and impairment of their capacity.
3. Establish a basis for design of a stormwater drainage control system which
    will preserve the rights and options of both the dominant and servient
    property owners. These rules and regulations shall apply to all non-farm,
    earth-disturbing activities performed on the unincorporated lands of Erie
    County, Ohio; except those activities as outlined in Section 1.30 of this text.
 

Section 2.10 Calculating Stormwater Runoff

The amount of stormwater runoff depends on a great number of factors. Some
of these factors are reasonably fixed and subject to accurate determination, such as watershed size and shape, ground slope and natural ponding. Others are seasonably variable, such as frozen soil, soil moisture condition, evaporation, or transpiration.  Still others vary by land use, such as type of ground cover and impervious areas or method of cultivation. Finally, rainfall is extremely variable as to seasonal conditions and other variable factors. Despite the indeterminate nature of these factors, methods for obtaining useful information about stormwater runoff have been developed. One of the four methods described in Urban Hydrology for Small Watersheds, Technical Release Number 55, by the Soil Conservation Service of the United States Department of Agriculture and its Ohio Supplement can be used to determine stormwater runoff or The Rational Method, as shown on Appendix E, which shall be the minimum design.
 

Section 2.20 Stormwater Runoff Control Criteria

Stormwater runoff control addresses both peak rate and total volume of runoff.
1. The storm drainage system installed shall carry a minimum five year 24
    hour frequency storm. The design of which shall conform to Appendix E.
    The retention/detention area shall have a minimum storage capacity for a
    ten year 24 hour frequency storm.
2. The peak rate of discharge from the retention/detention area shall not
    exceed a five year 24 hour frequency storm based on predevelopment
    conditions.
3. Storage volume does not have to be provided for off-site upstream areas.
    Flow from such areas will be routed through the drainage system in the
    development under consideration at a rate determined in the same manner
    as the on-site system. Off-site land uses over the last year before the
    development shall be considered as the predevelopment condition for the
    purpose of calculating changes in runoff.
 

Section 2.30 Runoff Control Methods

The runoff control criteria of this section necessitates the use of stormwater
runoff control facilities in many development situations. While the success of
such facilities for accomplishing a desirable level of runoff control cannot be
denied, it is often found these same facilities have the potential for adding to
neighborhood blight or a threat to public health and safety.
It is not necessary that the “cure” be worse than the “disease.” Stormwater
storage facilities can be functional and wholly unobtrusive. Their presence can
offer an added amenity to the urban environment. This positive impact can be
achieved by adherence to four basic steps in the implementation of stormwater
runoff control facilities. These are:
1. Proper selection of runoff control mechanisms.
2. Proper design of facility.
3. Construction of facility in strict adherence to design.
4. Regular maintenance program and designated responsibility for
    maintenance.
 

Section 2.40 Maintenance of Stormwater Drainage Facilities and
Control Structures

When stormwater drainage facilities and control structures that benefit more than one property owner are of a permanent nature the County will assume
responsibility for said structures once they have been constructed and are
functioning according to approved plans and once a “Perpetual Maintenance
Agreement,” under Section 6131.63 of the Ohio Revised Code, has been filed
and approved. Ownership and/or easements for the purpose of maintenance shall be granted to the County for access to all structures and facilities for which the County is assuming permanent maintenance responsibility.
Financing of the permanent maintenance of the control structures and facilities
shall be handled through a “Perpetual Maintenance Agreement;” whereby all
benefiting property owners of the improvement will be assessed their
proportionate share of the maintenance costs. These assessments will be
certified in accordance with Section 6131.63 of the Ohio Revised Code.
 

Section 2.50 Preparing a Stormwater Management Plan

A Stormwater Management Plan is required on all developments. The plan
development process is one which provokes thought and consideration of
management alternatives relative to stormwater early in the overall site
development process.
 

Section 2.50.1 Data Collection

Inventory the existing site conditions to gather information which will help you
develop the most effective stormwater management plan. The information
obtained should be plotted on a map and included with the calculations portion of the plan.
a. Topography -
    A 200-scale topographic map of the site should be prepared to show the
    existing elevations at two foot (2’) intervals or other intervals as deemed
    necessary by the Erie County Engineer. When drainage areas are large and
    cover areas off-site, USGS maps may be used to show these off-site
    drainage areas.
b. Drainage Patterns -
    All existing drainage swales and patterns should be located and clearly
    marked on the topographic map.
c. Soils -
    Major soil type(s) on the site should be determined and shown on the
    topographic map. Soil information can be obtained from the Soil Survey of
    Erie County, issued September 1975. Soil information should be plotted
    directly onto the map or an overlay of the same scale for ease of
    interpretation.
d. Ground Cover -
    The existing vegetation on the site should be shown on the topographic
    map.  Such features as tree clusters, grassy areas and unique vegetation
    should be  located on the map. In addition, existing denuded or exposed
    soil areas  should be indicated on the map.
 

Section 2.50.2 Runoff Calculations Before Development

With the completion of the Data Collection activity the peak rate of runoff and
runoff volume for the pre-development situation can be determined for the five (5) year storm.
 

Section 2.50.3 Data Analysis

When all of the data collected has been considered together, a picture of the site potential and limitations should begin to emerge. The Drainage Engineer should be able to determine those areas of the site which have potentially critical drainage hazards. The following are some important points to consider in site analysis.
a. Topography -
    The primary topographic considerations are slope steepness and slope
    length. Because of the adverse effect of long and steep slope on runoff,
    special care should be used in these potentially critical areas.
b. Natural Drainage -
    Natural drainage patterns exist on the land and should be identified on the
    plan so they can be incorporated into the proposed drainage system. Where
    it is possible, natural drainageways should be used to convey the runoff to
    avoid the expense and problems of constructing artificial drainage systems.
    Care should also be taken to be sure that the existing natural drainage
    system is not overloaded.
c. Soils -
    The major soil consideration from a runoff control standpoint is rate of
    infiltration of rainwater. Soils of the County have been grouped into
    hydrologic soil classes, which can be used to help determine the areas where
    critical runoff will occur.
d. Ground Cover -
    The type of existing ground cover greatly affects the amount of existing
    runoff from any given area. By knowing the types of existing ground cover
    and the proposed types, critical areas of runoff can be determined.
 

Section 2.50.4 Drainage System Development

After analyzing the data and determining the site limitations, the Drainage
Engineer can then develop a drainage system. He should work with the site
planner and attempt to locate the buildings, roads and parking lots to exploit the strengths of the site and overcome the drainage limitations of the site. The
following are some points to consider in making these decisions:
a. Fit Drainage Systems to Terrain -
    The Drainage Engineer should attempt to tailor the drainage system to the
    existing site conditions. This will avoid unnecessary land disturbance and
    therefore help reduce the increase in runoff.
b. Confine Construction to Areas Not in Drainageways -
    Any land disturbance in drainageways will necessitate the installation of
    more costly control measured.
c. Cluster Building Sites Together -
    Clustering building sites together outside of natural drainageways minimizes
    the amount of disturbed cover and helps reduce the increase in runoff.
d. Minimize Impervious Areas -
    Keep paved areas such as parking lots and roads to a minimum. The more
    land that is kept in vegetative cover, the more water will have a chance to
    infiltrate, thus minimizing runoff.
 

Section 2.50.5 Plan for Runoff Control

When the general layout of the site has been decided upon, a plan to control
runoff from the site must be formulated.
a. Divide the Site Into Drainage Areas
    Determine how much and where the runoff will travel over the site. Consider
    how runoff can be controlled in each drainage area. Remember, in most
    cases it is easier to control runoff in smaller areas than to try to handle the
    entire site at some location downstream as it leaves the site.
b. Select Runoff Control Practices
    Runoff control practices can be divided into three broad categories:
    ● Vegetative Controls
    ● Structural Controls
    ● Management Measures
    Local or State handbooks should be used to select and design appropriate
    vegetative and structural practices. Management measures are common
    sense types of controls used to help minimize the need for physical practices.
    1. Vegetative Controls
        Keep in mind that the first line of defense is to prevent increase in volume
        or rate of runoff. This is accomplished by protecting the soil surface as
        much as possible and not decreasing the over-land flow time.
    2. Structural Controls
        Where large increases in runoff occur, structural practices are generally
        the only way to control runoff. It is very important that structural practices
        be selected, designed and constructed according to standards and
        specifications of the engineer of jurisdiction. Improper use of inadequate
        installation can create problems which are greater than the structure was
        designed to solve.
    3. Management Measures
        Good site design and construction management is as important as any
        physical practices used for runoff control. The following are only some
        management considerations:
        a. Design site to help reduce runoff in open areas and not increase it.
        b. Use stage construction.
        c. Use as few pipe systems as possible.
        d. Allow runoff to travel around within the site and not just straight
            through.
 

Section 2.50.6 Develop Design Details

Once a development plan and drainage system that meets the runoff criteria has been decided upon, the detail plans for the drainage facilities and control
structures should be developed. Detail design plans shall be developed
according to generally accepted engineering principles and approved by the
County Engineer or the Engineer of Jurisdiction. It is important at this point in
time to work closely with the County Engineer or Engineer of Jurisdiction to make sure that all facilities and structures are being designed according to standards and criteria that exist for these types of facilities and structures within that jurisdiction.
 

Section 2.60 Preparing a Drainage Plan

Smaller site developments can result in major increases in runoff, but the
alternatives for handling them are usually limited. Wherever possible, we would
encourage the developer to go through all of the steps under Section 2.50.
However, in the situation where there is only one alternative for surface
development on a small site and it is merely a matter of designing a drainage
system to meet the runoff criteria, we only require submission of sufficient
information to show that the criteria is being met and that the drainage facilities and control structures have been designed to standard.
 

Section 2.60.1 Data Collection

In order to analyze the before development condition, the same data that is
required for a management plan is required for a drainage plan. Follow Section
2.50.1.
 

Section 2.60.2 Runoff Calculations Before Development

With the completion of the Data Collection activity, the peak rate of runoff and
runoff volume for the pre-development situation can be determined for the five (5) year storm.
 

Section 2.60.3 Runoff Calculation and Control Criteria

In most cases for small sites, the developer will know how the surface of the site is to be developed. He can then go directly to calculation of increase of runoff and determination of runoff criteria following the steps in Section 2.50.6.
 

Section 2.60.4 Plan for Runoff Control

From the results of Section 2.60.3, the developer can determine the type and
magnitude of control practices he will need, in most cases being some type of
structural control. These controls should be located on the site plan and runoff
calculations checked.
 

Section 2.60.5 Develop Design Details

Once a development plan and drainage plan and drainage system that meets the runoff criteria has been decided upon, then detail design plans for the drainage facilities and structures should be developed. It is important at this point in time to work closely with the engineer or jurisdiction to make sure that all facilities and structures are being designed according to any standards and criteria that may exist for these types of structures within that jurisdiction.
 

Section 2.70 Submission of a Drainage Plan

The plan submission shall consist of two parts:
1. Site Plan
2. Engineering details
The site plan is a series of maps pictorially explaining the information in the
narrative. The engineering details are detailed drawings, calculations and
specifications on the drainage facilities and control structures to be constructed
as part of the development.

CHECKLIST
FOR STORMWATER CONTROL PLANS
_______________________________________________________

SITE PLAN

_________ Vicinity Map –
                   A small map locating the site in relation to the surrounding area.

_________ Existing Contours –
                   The existing contours of the site should be shown on a map.

_________ Existing Vegetation –
                   The existing tree lines, grassy areas or unique vegetation should
                   be shown on a map.

_________ Soils –
                   The boundaries of the different soil types should be shown on a
                   map.

_________ Indicate North –
                   The direction of north in relation to the site should be shown.

_________ Existing Drainage Patterns –
                   The dividing lines and the direction of flow for the different
                   drainage areas should be shown on a map.

_________ Development Plan –
                   Location and size of all areas to be rendered impervious.

_________ Limits of Clearing and Grading –
                   Areas which are to be cleared and graded should be outlined on
                   a map.

_________ Location of Drainage Facilities and Control Structures –
                   The location of the drainage facilities and control structures to
                   be used on the site should be shown on a map. Facilities or
                   structures subject to section 2.40 shall be delineated.

ENGINEERING DETAILS
The following shall be submitted for drainage facilities or control structures to be constructed.

_________ Design calculations        ________ Design drawings

_________ Specifications                 ________ Quantities