Loading...
HomeMy WebLinkAbout1997-11-13 Work Session NEW HANOVER COUNTY BOARD OF COMMISSIONERS WORK SESSION, NOVEMBER 13, 1997 BOOK 26 PAGE 204 ASSEMBLY The New Hanover County Board of Commissioners held a Work Session on Thursday, November 13, 1997, at 10:15 AM. in the Conference Room of the New Hanover County Administration Building, 320 Chestnut Street, Wilmington, North Carolina. Members present were: Commissioners Buzz Birzenieks; Ted Davis, Jr.; Charles R. Howell; Vice-Chairman William A Caster; Chairman Robert G. Greer; County Manager, Allen O'Neal; County Attorney, Wanda M. Copley; and Clerk to the Board, Lucie F. Harrell. Chairman Greer called the meeting to order and reported the purpose of the Work Session was to hear a presentation by Mr. Dan Dawson, of Dawson Engineering, on the status of the storm water management study being performed on the Pages Creek Watershed. Mr. Dan Dawson expressed appreciation to the Commissioners for the confidence placed in Dawson Engineering to perform the study. The study team consisted of Herb Fox, who is retired from Soil and Conservation Service with 30 years of experience in hydrology work; Charlie Hollis, Chief of the Regulatory Branch of the Corps of Engineers; Roy Tyndall, Floodplain Management Branch of the Corps of Engineers; Applied Technology and Management; and Dawson Engineering. Mr. Dawson reminded the Board that the concept of the study was to basically study the hydrology of the watershed and the runoff of rainfall events. From an analytical assessment, findings can be used to address drainage issues throughout the County. He reported the objectives of the study are to assess the watershed condition, to predict the outcome of any future developments, and to identify ways of improving water quality. Although storm water runoff has always been a major concern for the Commissioners and citizens of the County, last year's hurricanes have focused more attention on flooding than water quality. The public is demanding help for those who are suffering from the flooding conditions caused by channel blockages or culverts of inadequate size. Because of budgetary constraints and UNCW's study efforts in water quality for the past three years, it was decided that the Pages Creek Watershed Study would focus on hydrology. However, UNCW Center for Marine Science and Research has provided a base line of the area's water quality and will continue their investigations. The hydrology study assessed the watershed to establish current and future predictions of undeveloped area impacts and to evaluate alternatives to improve drainage. The next step in the process is to receive public comments. The study team will need to know who has drainage problems or water quality concerns in the Pages Creek area. However, general concerns from those in other parts of the County will be considered in developing a drainage policy. Mr. Dawson announced the public meeting is scheduled for December 4, 1997, at Ogden Elementary School. Commissioner Birzenieks asked ifUNCW will be at the public meeting to discuss the water quality research since Mr. Dawson will be dealing with hydrology? Mr. Dawson responded that UNCW has not been asked to participate, but it may be helpful. His intent would be to give a summary of the findings and receive comments from the public on what they perceive as the main issues. These opinions will be an integral part in developing a policy on what needs to be done about flooding and water quality concerns. Mr. Dawson pointed out Pages Creek in the aerial photograph and noted the limited amount of undeveloped land in the watershed. Most of the undeveloped lands are floodplain or wetland soils, where State and Federal regulations will prevent further development. The hydrologic study used data of two, five, ten, twenty-five, fifty, and one hundred-year rainfall events to determine the impact of drainage in the area. In adopting a storm water management policy, the Commissioners can consider the analysis on pre- and post-development NEW HANOVER COUNTY BOARD OF COMMISSIONERS WORK SESSION, NOVEMBER 13, 1997 BOOK 26 PAGE 205 based on the more frequent events, as well as the extreme events. The rainfall in a twenty-four-hour period ofa two-year storm is estimated at 4.5 inches of rainfall. However, in a hundred-year event, a twenty-four-hour storm is estimated to have 10 inches of rainfall. During a hurricane, most of the flooding in Pages Creek is the result of wind setup and storm surge from Mason's Inlet and not from storm-water runoff. Mr. Dawson explained the precipitation rates used in the analysis were based on weather records and are the accepted way to predict storm-water runoff. Furthermore, the impacts of the tides on drainage of culverts were considered in the analysis. To evaluate the six-square-mile drainage basin, the study divided the area into twelve sub- basins. The tidal marsh was treated as a receiving pond or stream because of the flat level. Topography, land use, soils, flood zones, and current State regulations were considered in making the evaluation. In predicting discharges on future development areas, a conservative approach or "worse-case scenario" was applied. The current State rules reduced runoff by 50%. When properly enforced, State regulations have a fair amount of protection on the volume of runoff. The Technical Release 20 Program (TR-20) was used to model the watershed area. Additionally, an inventory of all 24-inch drainage culverts and channels was taken and analyzed to determine how they were functioning. Mr. Dawson reported large metropolitan areas, such as Greensboro and Charlotte, have already been required to analyze runoff as part of the NPDES storm water permitting process. In 1999, the EP A will decide whether counties or cities will lead the work of separate storm water sewage system programs. Eventually, the work being performed in Pages Creek will need to be done for the entire county as part of the on-going Clean Water Act of 1972. This will be an unfunded mandate by the Federal government. As part of the inventory process, the study team found twenty culverts that were causing flooding problems; but the cost to remove and replace these culverts is $290,000 to $300,000. In storm-surge flooding, the size of the culvert will not make a difference. But in the more frequent events, ten years or less, the correct culvert size makes a difference. To clean and dredge the channels and streams that connect to the culverts from the upper reaches of the watershed to the creek will cost $4.6 to $5 million. The State will need to approve any land disturbances and the Corps will not want 404 Wetlands affected. Ultimately, constructed wetlands will need to be built near outlets of the channels before the State will allow dredging of the creek. The water must flow through the constructed wetlands and the natural wetlands before entering the creeks. In the final analysis, the cost of the environmental permitting issues may prohibit the project. Mr. Dawson gave the following suggestions to consider: 1. In addressing drainage from a watershed point of view and not a site-by-site basis, some of the County's watershed areas are partially located in the city limits. The County may want to coordinate with the City on how these watershed areas will be managed. 2. County departments, such as Planning and Engineering, may not have adequate staff support for additional projects. Planners, hydrologist, and engineers will be needed. In reviewing the maps and charts of Pages Creek Watershed, Mr. Dawson pointed out the factors considered in the analysis: 1. The maximum density predicted on undeveloped land was based on regulations ofthe Land Use Plan, Zoning Ordinances, and State regulations. NEW HANOVER COUNTY BOARD OF COMMISSIONERS WORK SESSION, NOVEMBER 13, 1997 BOOK 26 PAGE 206 2. In calculating the peak discharge in cubic feet per second for water moving through a channel or pipe at one foot per second velocity, the total volume of runoff in acre feet was based on an acre being 200 feet by 200 feet by one foot deep. (Acre = 200' x 200' xI') 3. The predicted runoffis based on the most extensive development allowed by Zoning, Land Use, and State regulations, and will give an estimate of what needs to be done to keep drainage from getting worse. Mr. Dawson explained the total creek runoff discharge for a two-year event if the land is completely developed, will be 20% more in volume. In a 100-year event, the increase is less than 10%. This information can be used to decide if something more should be done from a land use or regulatory point of view that will protect the creek. Without State controls, the increase would be 30% for two-year events and 25% on 100-year events. He further pointed out that if development was stopped, it would prevent a 10% increase in runoff volume for the 100-year event or a 20% increase for the two-year event. Mr. Dawson recommended watershed planning needs to be included in future drainage programs so that areas like NorthChase could have better managed drainage. The County's current regulations should have consistent standards. In getting a permit for a shopping center, the State's storm-water and erosion control rules are being used. Yet no one checks the hydrologic capacity of the internal drainage pipes that collect the water from the parking lots of the shopping centers going to the storm-water ponds. The State checks the pond for adequate surface area and holding capacity. The County's Erosion Control officer determines if soil erosion is managed on site, but not at the long-term culvert capacity in the parking lot. Currently, the County depends on private engineers to design projects properly. He recommended the County perform a detailed study on culvert sizing similar to the City's drainage program. At this time, NCDOT does not have a maintenance program on undersized culverts. Because there has been so much development in the last twenty years, the County may want to ask NCDOT to replace the undersized pipe. To continue the initiative that has been taken, Mr. Dawson suggested the Commissioners budget funds for drainage programs. Ten or 12 constructive wetlands will cost $32 million; but the County could start with a $1-$2 million constructed wetland project. The Corps and the State will allow constructed wetlands to handle drainage for future developments in a watershed area instead of a pond. Instead of a developer using 10-12% of his property for a pond, he could pay a watershed assessment or something similar that could be used for constructing wetlands. He suggested to start a pilot program for constructed wetlands in the Pages Creek area. By working with the Center of Marine Science Research, EP A, the Corps of Engineer, and the State, the County could determine if less land is needed to treat water before entering the tidal marsh. If so, the land requirement for constructed wetlands may significantly decrease. In conclusion, Mr. Dawson advised the County's current regulations on drainage have inconsistent outcomes because they have not been uniformly enforced. Drainage standards are very important and should be formalized, as well as integrating watershed plans. The EP A's NPDES program will be mandated in a couple of years. Mr. Dawson urged the Commissioners to expand the Pages Creek project to other areas in order to protect water quality in the county. The County may want to work with the City to deal with the watershed in the newly annexed area around Howe Creek. A joint storm water management program may be needed because of the overlapping of political boundaries. Mr. Dawson reported the Pages Creek Watershed Study should help the Commissioners make an informed decision. Although all the problems of water quality and drainage cannot be solved, the public will need to understand the issues facing the Commissioners. After the public input is received, a final report will be submitted to the Commissioners in January consisting of the proposed storm water ordinance and storm water design manual. NEW HANOVER COUNTY BOARD OF COMMISSIONERS WORK SESSION, NOVEMBER 13, 1997 BOOK 26 PAGE 207 Vice Chairman Caster asked if the public meeting will address drainage concerns of other areas besides Pages Creek? Mr. Dawson responded an aerial photograph of Pages Creek will be on display. The public will be asked to mark their area of concern on the map and write their concerns on a card. People from others areas will be given the same opportunity to write down their concerns, which may be similar to those of Pages Creek. The public will need to convey which is more important, water quality or hydrologic capacity. With the public input, the study group will determine where specifically to address a flooding problem. The study may surmise that constructed wetlands should be tested near a certain location that has drainage problems. Assistant County Manager, Dave Weaver, emphasized the importance of understanding that the process and standards initiated in the Pages Creek Watershed Study should be transferrable to other watershed areas in the County. Discussion was held on the estimated cost of $3 7 million for completion of the Pages Creek Watershed project. Commissioner Birzenieks asked if that cost would be similar for other watershed areas in the County. Mr. Dawson estimated the cost for the six square mile watershed would be $6 million per square mile. The expectation from the public is to fix drainage problems. Even if money is available, the environmental regulations that protect water quality may prevent using some of the solutions. The established data taken from the watershed area can calculate the predicted runoff of a wooded area being changed to a single family or commercial development. If a database of storm water runoff was collected from all over the county, a model could predict the outcome of a proposed development. As part of the public policy, the Commissioners can decide that before a property can be developed, it must correct the hydrologic capacity downstream. Until a uniform database of existing conditions is made, resolving issues between property owners may be difficult. Chairman Greer asked Mr. Dawson if he was aware of the American Heritage Rivers Program, and if so, would the program protect watersheds? Mr. Dawson responded the American Heritage Rivers Program would integrate with programs, such as the Cape Fear River Corridor Study. The program would apply to communities on the larger type rivers such as the Mississippi. Chairman Greer requested Mr. Dawson to find out what he could about the program and report to him before the next Board meeting scheduled for November 17, 1997. ADJOURNMENT Chairman Greer expressed appreciation for the informative presentation. The meeting was adjourned at 11 :35 AM. Respectfully submitted, Lucie F. Harrell Clerk to the Board