Unlike sanitary sewer and water systems stormwater flow is naturally occurs by way of swales, creeks, and rivers, each of which contributes to a larger drainage area called watersheds. This means that the City cannot impair, and needs to proactively maintain the integrity and capacity of these naturally occurring features. While storm sewers and stormwater management will not limit the intensity of development, the allowance for appropriately sized facilities on each development is important. The creation of the Stormwater Master Plan and its recommendations for the 1997 Community Plan gave the City a strong base for managing stormwater.
The Stormwater Master Plan was created based on models of each stream that flows through the city to the Scioto River. The results of the 1997 modeling identified deficiencies in the system many of which have been addressed through the City’s Capitol Improvements Program. These projects have included two phases of storm sewer installation in Historic Dublin, channel improvements along Clover Court and Shier Rings Road, the Aryshire Drive culvert replacement, and bank stabilization of the North Fork Indian Run along Brand Road. An audit of the North Fork Indian Run watershed showed that the regulations are controlling the runoff from developed sites at rates so that stream levels have not increased since the initial model was performed.
Another result of the previous modeling and investigation efforts was the identification of the need to implement new stormwater management regulations. The initial version resulted in Chapter 53 of the Codified Ordinances passed by City Council in 1998. These regulations included the first codified requirements for control of both quantity and quality of stormwater runoff in Central Ohio. This practice has subsequently been incorporated into the Ohio Environmental Protection Agency’s (OEPA) General Construction Permit with some minor variations. To comply with the state regulations, City Council adopted a revised version of the Stormwater Regulations in 2005. This version of Chapter 53 also contains Stream Corridor Protection Zone regulations.
The regulations implemented since 1998 have required conservative allowable stormwater runoff from development sites. There were five watersheds where the significant development occurred: North Fork Indian Run, South Fork Indian Run, Cosgray Creek, Cramer Creek and Billingsley Creek. The Stormwater Master Plan contains predetermined release rates for each watershed. New modeling will aid in identifying any additional deficiencies for inclusion within the Capital Improvement Program.
The Stormwater Master Plan Update, completed in 2009, had three primary goals: (1) update the modeling for the watersheds that experienced the most significant development growth; (2) update the capital improvement program projects recommended by the 1999 plan; and (3) forecast future regulatory impacts on the City’s stormwater management program.
To update the modeling, stormwater management plans on file were reviewed for all previous developments that were not part of the initial modeling, field visits were made to verify the infrastructure, and the computer model was updated and the results analyzed. This review noted 165 new stormwater management facilities that were added to the system, only 30 of these were not constructed per the approved construction drawings. The analysis and findings of this portion of the update included:
- Wright’s Run (Billingsley Creek): no new locations of stream bank erosion, deficient storm sewers, culver overtoppings or structural flooding.
- Cosgray Creek: two new locations of stream bank erosion, no deficient storm sewers, and two culverts that overtop in the 100 year event (under Shier-Rings Road (previously identified) and a driveway near Wilcox Road).
- Creamer Creek: three new locations of stream bank erosion, a section of deficient storm sewer in the Heather Glen subdivision, and no new culvert overtoppings or structural flooding.
- North Fork Indian Run: three new locations of stream bank erosion, no new pipes identified as deficient, and no new culvert overtoppings or structural flooding.
- South Fork Indian Run: one new locations of stream bank erosion, no new pipes identified as deficient, and one culvert overtoppings was identified.
These model results confirm that the City’s current stormwater release rate policy provides consistent and accepted criteria throughout the city and has had a significant impact on minimizing effects of development to the receiving streams.
Three new capital improvement projects were identified through the modeling work: Hawk’s Nest Improvements (storm sewer installation to alleviate standing water), Heather Glen Improvements (increase pipe size or add detention), and Glencree Place Improvements (storm sewer installation to alleviate standing water).
The future of stormwater regulations will evolve to include more prescriptive requirements for specific watersheds, numeric effluent limits, minimum control measures, encouragement of low-impact development design and retrofits to restore urban hydrology. While Dublin has required stormwater controls for quantity and quality since 1998, the City should consider changes to promote retrofits and low impact developments and should continue to coordinate with the OEPA on proposed changes to the statewide regulations for stormwater and erosion control.
Stream Corridor Protection Zones have added a layer of protection for stream corridors that may have otherwise been adversely effected by development and where no other regulations provided for the preservation of the riparian buffers. These zones apply to streams within Dublin that do not have federally designated floodways or floodplains. These zones will also aid to protect residents from impacts of flooding and land loss through erosion. The map above depicts the locations where a Stream Corridor Protection Zone may apply. The exact location and width is determined by specific criteria in the Code.
Crossing of a Stream Corridor Protection Zone for roadways is restricted. Crossings can be permitted if alternative roadway locations are demonstrated to be infeasible and disturbances within the Stream Corridor Protection Zone will be minimized and mitigated.
A limited number of uses are allowed within a Stream Corridor Protection Zone. These include recreational activity, removal of damaged or diseased trees, and establishment of new vegetation or reforestation. Other projects or work can be considered where an environmental and public benefit is demonstrated. Disturbance of the Stream Corridor Protection Zone for these activities can be mitigated through re-vegetation or reforestation.
The following activities are prohibited in a Stream Corridor Protection Zone per the City Code: construction, dredging or dumping, disturbance of natural non-invasive vegetation, parking, new surface and/or subsurface sewage disposal or treatment areas, fences, walls, new agricultural activities, industrial or commercial businesses, ditching/diking, changes in topography, removal of topsoil or use of herbicides and pesticides.
The following facilities are prohibited in a Stream Corridor Protection Zone: buildings/structures, swimming pools, signs, billboards, utility lines or pipes (except as approved by the City), electric lines (with the exception of transmission lines), telecommunications lines (with the exception of transmission lines), cable TV lines and stormwater management facilities.
Analysis and Future Projections
Each state is required by Section 303(d) of the Clean Water Act (33 U.S.C. 1313), to submit a prioritized list of impaired waters to the U.S. Environmental Protection Agency (EPA) for approval. The list indicates the waters of Ohio that are currently impaired and may require total maximum daily load (TMDL) development in order to meet water quality standards.
TMDL reports identify and evaluate water quality problems in impaired water bodies and propose solutions to bring those waters to attain water quality standards. TMDLs are established for phosphorus, sediment, fecal coliform bacteria, dissolved oxygen, ammonia, floodplain capacity, bed load, and habitat. Some of the recommended solutions to address the impairments include storm water controls, point source controls, manure management, and habitat improvements. As part of the federal Clean Water Act, the U.S. EPA must review and approve each TMDL.
Ohio’s 2006 TMDL priority list was approved by the U.S. EPA on May 1, 2006. The list and schedule are contained in Appendix D.2 of the 2006 Integrated Water Quality Monitoring and Assessment Report and contains both the Scioto River and the Big Darby Creek. Prepared in accordance with federal guidance issued in July 2005, the Integrated Report satisfies the Clean Water Act requirements for both Section 305(b) water quality reports and Section 303(d) lists. The report describes the procedure that OEPA used to develop the list and indicates which areas have been selected for TMDL development during FFY 2007 through 2008. The Ohio EPA is moving forward on many TMDL projects, and a map of Ohio TMDLs in progress is also available from the Ohio EPA.
Currently, the land use planning boundary coincides with the limits of the watersheds that drain to the Scioto River. Development within the corporate limits of the city farther west or north of the current planning boundary could occur within the Big Darby and Little Darby Creek watersheds. Specifically, areas west of Dublin’s current service area drain to Sugar Run, which is a tributary to the Big Darby Creek.
The Big Darby Creek Watershed TMDL Report that was approved by the U.S. EPA on March 31, 2006, states:
“The Darby Creek watershed, including Big and Little Darby creeks, is an important water resource in Central Ohio. Natural resource professionals from private, public and academic institutions are unanimous in citing these streams as among the most biologically diverse streams of their size in the Midwest. Big and Little Darby creeks have been designated as State and National Scenic Rivers, and the watershed is known to provide habitat for several state and federally listed endangered species.”
The Ohio EPA has created specific regulations for stormwater management of this creek. Any regulations that are more stringent than Dublin’s municipal regulations must be adhered to by development projects in the future.
Water quality assessments were performed by the OEPA in 2010 for their two assessment units that cover the City of Dublin: Indian Run (North and South Fork) watershed and Hayden Run – Scioto River watershed. The assessment placed these watersheds in Reporting Category 5 which means that the water quality is impaired and a TMDL is needed. A technical support document (TSD) is scheduled to be available by the OEPA for viewing by late 2012 or early 2013. The TSD contains the results of the initial survey, including presentation of raw data, as well as some synthesis and interpretation of the results. A TMDL report is likely to be completed by the end of 2013 by the OEPA. This will report the results of a follow-up study to quantify the magnitude of the pollution problem from all of the relevant sources and prescriptions for a reduction in pollutant loading from those identified sources.
In 2008 and 2009, the OEPA issued renewal permits for both the General Construction Permit and the Small Municipal Separate Storm Sewer Systems, respectively. Dublin is required to adhere to the requirements of both of these permits. Fortunately, the renewals did not contain any new requirements that necessitated changes to our practices or regulations.
Bridge Street District
Existing modeling was used to determine the impact on the stormwater system from the proposed development of the Bridge Street District. The impacts to the system will be minimal and can be best managed with an integrated approach when development occurs. An integrated approach will include stormwater management within the site by way alternatives to traditional ponding of stormwater, and will include the use of green roofs, permeable pavement, bio-retention facilities, rain barrels, planter boxes, etc. These practices demonstrate the future of stormwater management and will allow for optimizing the land for creating the urban and walkable community desired. A revision to the Stormwater Design Manual has been completed to facilitate and guide the use of these types of stormwater management facilities.
Conclusions and Recommendations
Stormwater flow and management continues to be an important part of the City’s infrastructure system. Further investigation is recommended into a user fee to provide for maintenance and work that may be needed to meet state and federal regulations. Also, the City’s regulations regarding water quality, the management of stormwater, and the preservation of the natural stream corridors should be periodically reviewed and updated to comply with state and federal regulations as well as best management practices.