680 Storm Water Disposal Comprehensive Plan Section 680

Transcription

1 Comprehensive Plan Section 680 STORM WATER FACILITIES PLANS Since 1975 there have been four storm water studies completed: A Storm Water Facilities Plan for the Owensboro Metro Area, by G. Reynolds Watkins in The Owensboro Flood Abatement Study, by Johnson, Depp, and Quisenberry (JDQ) in The Owensboro-Daviess County Drainage Implementation Plan, by JDQ in Storm Water Master Plan, by Quest Engineers, Inc. in 1999 for the City of Owensboro. The 1975 study evaluated the major drainage systems which convey runoff from the urbanized area, but did not include the storm evaluated problem areas, proposed specific capital improvements for ten projects totaling $2,270,000 in 1975 dollars, and recommended storm water controls on new development. It also recommended the creation of a City- County Drainage District. The 1979 study was more limited in scope and focused on recommendations and improvements to the Scherm, York, and Devins ditches. The purpose was to increase the capacity of the ditches to convey a 25-year design storm and was estimated to cost $1,176,000 in 1979 dollars. The JDQ study in 1980 evaluated drainage problems in six separate watersheds (Devins, Carter, Tamarack, Fairgrounds, Harsh, and Scherm). Costs were estimated at $11,369,400 in 1980 and would have increased the capacity of the drainage areas to convey a 25-year design storm. The remainder of this section will focus on the most recently completed plan. Although the proposals are for the City of Owensboro, it is important to note that doing the evaluation of the various watersheds, two of the four considerations used were aimed at not exacerbating the existing drainage problems in the County. The two considerations were: Detention facilities are recommended at the downstream end of each watershed to mitigate the increased runoff rate resulting from construction of proposed storm water facility improvements. Runoff rates into the County will be the same or less than what now exists. Where existing channels in the County are inadequate to convey the 25-year storm event, a recommended channel widening or detention volume is provided that enables the runoff to stay within the channel banks. STORMS AND FLOODING According to A Storm Water Facilities Plan for the Owensboro Metro Area, storm water in the relatively flat Owensboro metro area falls into three major drainage basins: The Ohio River, Panther Creek, and the Green River, as shown by Exhibit 683- M1. Within the Owensboro urban area, most storm water is carried to the Ohio River by underground pipes. In the Green River and Panther Creek basins, however, surface channels originally constructed as agricultural ditches carry the storm water. These channels run through land that has very little slope. Therefore, the velocity of storm water flow is restricted, and the low velocities, in turn, are unable to scour the banks of trees and brush which further impede water flow. The maintenance of these surface channels presents an unusual and extreme burden for local government. Contrary to popular belief, Panther Creek generally has very little effect on flooding within the Owensboro urban area. Flooding in the Panther Creek area most often is the result of winter or spring storms of low intensity, but high duration -- maybe 4 or 5 inches for 1 or 2 days. This brings Panther Creek to a high stage, which, in turn, produces a backwater effect on other streams within a mile or so of Panther Creek. To alleviate flooding of this type, all of Panther Creek would have to be improved, as well as the many surface channels serving Owensboro. In the summer and early fall, a different type of storm usually occurs. Before the storm, the ground is dry and channels empty, but the rainfall is so intense and of such short duration that flash flooding takes place. This type of flooding presents the most pressing problems to the Owensboro urban area -- and its alleviation requires localized surface drainage improvements. THE 1999 STORM WATER MASTER PLAN Objectives of the plan include: Develop a plan that would be used on a day-to-day basis as a practical guide for storm water management. Maximize the use of existing data. Establish an expected level of protection. Achieve a substantial reduction in flooding. Develop a prioritized list of storm water improvements. Communicate effectively during the plan preparation through a storm water advisory committee. ADVISORY COMMITTEE During plan preparation information was shared with and input received from the Storm Water Advisory Committee. Members included representatives from: Mayor s Office City Manager s Office City Engineer s staff County Engineer s staff Regional Water Resource Agency Planning staff Interested citizens Local engineering firms Quest/CDP engineers The committee provided invaluable assistance in discussing and reaching consensus on the level of protection, prioritization methodology, implementation and other primary issues. STUDY AREA Drainage systems conveying storm water within, away from, and into the city limits of Owensboro were addressed in the Storm Water Master Plan. Major systems consisted of drainage facilities greater than or equal to an equivalent 36-inch pipe. Drainage facilities less than an equivalent 36-inch pipe are designated minor systems in the plan. Minor systems were included only where required to evaluate any of the 30 specific locations identified by city staff as flood prone. The 13 major systems and related watersheds include: Persimmon Ditch Goetz Ditch Gilles Ditch Target Ditch Devins Ditch Harsh Ditch Rhodes/York Ditch Horse Fork Carter Road Ditch Yellow Creek Scherm Ditch Middle School Tamarack Ditch

2 DATA AND EVALUATION Existing data used in the plan included a number of maps and related text that provided information on the existing boundaries of the watersheds; zoning, topography, soil, & floodplain areas; and storm, sanitary, and combined sewer systems. City staff also provided information on 30 specific areas that had been identified as flood-prone (shown on Exhibit 683-M1). New data also had to be developed. The determination of which design storm event -- 2, 10, 25 year, etc. -- for which to plan would dictate the needed data and analyses. To decide this, two typical systems were thoroughly studied: an urban closed-conduit (Scherm) and a rural open-conduit (Persimmon). The results were extrapolated to the overall drainage system to estimate the costs for improvements for the respective storm events. To effectively handle a 25-year storm would not cost significantly more than for a 10-year storm, which the Advisory Committee deemed to be the minimum design objective. Therefore, the consensus of the Advisory Committee for the design storm (level of protection) on which the plan would be based was the 25-year event. Inventory data for the 13 major systems was then gathered, including horizontal and vertical control. FEMA s model was available, so compatible software was used to study hydrology, hydraulics, and culverts. Models are necessary to quantify the runoff from a watershed and the routing of the storm water through the existing storm water drainage facilities. Due to the size of the Harsh and Horse Fork watersheds, they were subdivided into their main channel and tributaries. This resulted in evaluation of 21 watersheds (see Exhibit 683-M1). The models calculated the amount of runoff, the route through the existing system, where existing facilities were inadequate to convey the 25-year event, and recommended improvements. Detention facilities and diversion channels were incorporated to maximize the use of existing facilities and minimize the magnitude of proposed facilities. The Horse Fork #2 watershed was the only one of the 21 sheds evaluated that did not require any improvements to convey the 25-year storm. Improvements to the other 20 watersheds were combined into 71 separate projects at an estimated total 1999 cost of approximately $64 million. PRIORITIZATION AND IMPLEMENTATION The 71 projects are recommended for implementation over an extended time frame, therefore, the projects were prioritized. City staff and the Advisory Committee developed twelve criteria that were applied to each of the 71 projects. Next, the priority of each watershed was made using downstream improvements as a basis to determine importance. Finally the staff, consultants, and Advisory Committee evaluated each watershed by focusing on the critical issues of flooding, accessibility and health/safety. Exhibit 682-T1 provides the resulting priorities. Exhibit 682-T1: Watershed Priorities 1. Harsh JR Miller 8. Persimmon Ditch 15. Horse Fk Main 2. Scherm Ditch 9. Harsh Ditch West 16. Horse Fork #3 3. Devins Ditch 10. Rhodes/York Ditch 17. Horse Fork #1 4. Goetz Ditch 11. Horse Fork #4 18. Middle School 5. Harsh Ditch Main 12. Carter Road Ditch 19. Gilles Ditch 6. Tamarack Ditch 13. Yellow Creek 20. Target Ditch 7. Harsh Ditch E. 14. Horse Fork #5 The first seven projects, indicated in bold type in the exhibit, were deemed the most critical and should be implemented first. Following completion of the initial projects in the first seven watersheds, it becomes more important to complete the remaining projects in these watersheds based on their evaluation score and their designation as a downstream project. This methodology yielded the following results: Completion of the initial group of projects in the top seven watersheds and the resulting visible improvements will assist in gaining public support for the storm water program. Random or subjective project selection will be eliminated and with it the potential for negative impacts and political influences. Downstream projects will be completed first. Implementation Implementation is dependent on the level of funding that is available. Regardless of where the funds come from, it was assumed that $4 million would be available annually. This funding was never realized. However, through the Your Community Vision funds, approximately $1,000,000 has been earmarked annually for these projects. The following is a list of projects to be completed: Exhibit 682-T2: Project Implementation Project Name Description Goetz Phase 3 Texas Gas to Placid Place (G-52~G- 58ax Harsh Phase 1C Daviess St to St Ann (HJR-120~HJR- 155) Goetz Phase 4 Texas Gas to College Drive Harsh Phase 1D St Ann St to Newton Parrish School to Byers Ave (HJR-155~HJR-132) Harsh Phase 1E Byers from Adams St to Frederica St Harsh Phase 1F Newton Parrish School to Hawthorne Design Scherm Design of Scherm Phases I & III Scherm Phase 1A 75 acre foot Detention Basin Scherm Phase 3 Christie Place to South Griffith (S-56~ S ) Design Devins Design of Basin and Pipe System Devins Phase 1 Detention Basin and line to Persimmon Ditch Design Harsh Design Horse fork and Harsh 2A~2C Horse Fork Phase 1 Detention Basin Harsh Phase 2A Bypass to 2 nd Veach Crossing (HM- 2~HM-14) Harsh Phase 2B 2 nd Veach Crossing to North End of Live Oaks (HM-14~HM-269 Harsh Phase 2C North End of Live Oaks to Owensboro Christian Church (HM-26~ HM42) Scherm Ditch Start design and construction of Windsor Ave Leg of Sherm

3 Exhibit 683-M1: Storm Water Facilities

4 URBAN STORM WATER MANAGEMENT ADMINISTRATIVE AGENCIES Within the City of Owensboro, storm water facilities are a city responsibility -- but for the remainder of Daviess County, responsibility lies with the Daviess County Fiscal Court. Unfortunately, storm water flow recognizes only gravity, and not political boundaries. Due to the pattern of drainage systems in the Owensboro Urban Service Area, a storm water problem and the proposals for its alleviation often relate to both political jurisdictions. Corrective action depends upon the joint and cooperative efforts of both City and County. The 1980 Drainage Implementation Plan as well as the 1975 Storm Water Facilities Plan recommended the formation a Joint City-County Drainage Commission. This commission would employ its own staff who would concentrate on storm water problems. It would be funded by the City, County, and/or other sources. In the mid-1990s, when the Regional Water Resource Agency was being formed as the city-county sanitary sewer agency, the City and County considered including a storm water utility as part of RWRA s responsibilities. Ultimately, this did not come about. CONTROLS ON NEW DEVELOPMENT The high cost of correcting past mistakes or oversights should provide additional incentive to ensure that similar mistakes are not made as future development occurs. To this end, the 1975 Storm Water Facilities Plan also recommended several actions to be taken in regard to new development that remain valid and viable. These recommendations included: Full review of storm water needs for new development prior to approval by the City, County, or Planning Commission. Note: This is currently implemented through regulatory review and approval of development plans and subdivision plats. Use of detention facilities wherever possible to accommodate excess floodwaters on-site, rather than simply pushing them further downstream and providing for their proper long-term maintenance. Note: Currently, detention basins are required for most new, urban development. Responsibility for long-term maintenance varies basin to basin; most basins are privately maintained, but some, newer basins have been accepted for maintenance by the City. Giving proper consideration to the entire drainage basin affected, rather than only to the area of the property under development. Note: Currently, this is possible only rarely. With federal assistance, securing a more detailed definition of the 100-year flood plain, and developing appropriate mechanisms for protecting the area from inappropriate development. Note: There have been two flood studies conducted by the Federal Emergency Management Agency since As a result, flood plain maps and zoning regulations were first adopted in the fall of The current Flood Insurance Rate Maps became effective March 3, RURAL DRAINAGE IMPROVEMENTS CREEK AND DITCH CLEANING For fiscal year 2000, the Daviess County Fiscal Court budgeted $250,000 to address drainage issues in the unincorporated areas of Daviess County. Under the 50/50 Program, the County will split the costs half-and-half with rural property owners who propose qualifying drainage improvement projects. Most of the FY 2000 funds have been used to perform major clearing and cleaning projects for several drainage ways including, among others, Blackford Creek along the Hancock County line in northeastern Daviess County, Fulkerson Ditch near Stanley, and sections of Panther Creek. These projects involve the use of a 60-foot excavator machine to remove trees, beaver dams, sandbars, and other obstructions to the free flow of water. The County Engineer has prepared an inventory of all rural drainage channels, including their conditions and other characteristics, which should allow a priority list to be prepared for an ongoing, clearing and cleaning program. In 2003, the County Engineer prepared a priority list for some thirty channels and ditches of high importance to Daviess County over all of the drainage systems. Since that time, Daviess County has been on a regular basis cleaning and clearing those channels in addition to others that are not on the list but deemed necessary for the overall drainage. PANTHER CREEK IMPROVEMENTS Panther Creek and its tributaries drain 371 square miles of land. Floods in this basin inundate residential and agricultural portions of a large part of central Daviess County. The 100-year flood plain extends into the Owensboro urban area at several locations (see Exhibit 743-M1). As noted in the 1997 Flood Insurance Study, the U.S. Army Corps of Engineers, in 1968, completed a clearing and snagging project for the main stem of Panther Creek and its major tributaries. In FY 2000, the County is repeating a clearing and snagging effort. Such efforts can improve the rate of flow of storm water, thereby reducing the magnitude of flooding for a given storm event, especially for smaller storm events. In 1997, the Corps investigated the costs vs. benefits of constructing numerous, high-volume detention basins at strategic points along Panther Creek. During storm events, water would be detained in holding basins along Panther Creek, then released slowly downstream. This technique might reduce the frequency of localized and lesser flood events that aggravate particular areas each year. However, the larger and more widespread that storm events become, the less effective this system of basins would become. For example, in a widespread 10-year storm, the backwaters of the Green River impact Panther Creek 13 miles upstream from the Green to around KY 279 South. This slows the rate of flow on Panther Creek further upstream. Because there is no capacity downstream, water spreads out over a large, relatively flat area.

5 FLOOD CONTROL DETENTION BASINS The Daviess County Fiscal Court aggressively took on another approach to improve the overall drainge by building flood control detention basins distributed in key and important flood potential areas across the county. Those basins were financed through local and federal funds and constructed in locations as recommended by the most recent study, the 1999 Storm Water Master Plan by Quest Engineers. The following projects have been built by the county in the past several years: Gilles Basin on Gilles Ditch Horse Fork Basin on a tributary of Horse Fork Creek Harsh Basin on Harsh Ditch