Joint Flood Mitigation Plan
Genesee & Wyoming Counties Joint Flood Mitigation Plan
(Tonawanda & Oatka Creek Watersheds)
Executive Summary
The communities along the Tonawanda and Oatka Creek in Genesee and Wyoming Counties have experienced several floods in the past, resulting in severe damage to residential, commercial, and public property as well as risks to the safety of residents and others. In 2000 Genesee and Wyoming Counties Emergency Management Offices, as lead agencies on behalf of the towns, villages, and city applied for, and was awarded a Federal Emergency Management Agency (FEMA) Flood Mitigation Assistance - Planning Grant from the New York State Emergency Management Office for the Joint Flood Mitigation Plan Project.
The goals of the Project were to develop a watershed-wide and municipal approach for mitigating and reducing flood hazards along the Oatka and Tonawanda Creek in Genesee and Wyoming Counties and to adopt plans for participating communities that identify the most effective means of implementing measures to eliminate or reduce the impacts of flood hazards.
Beginning in November 2002, the Joint Flood Mitigation Planning Committee was formed. It initially included representatives from each county’s Emergency Management Office, Planning Department and Soil and Water Conservation District. The Committee expanded its membership to include a representative from each participating municipality to review flood risks and hazards, encourage public involvement, develop mitigation activities, and recommend action steps to alleviate flood-related problems. The Flood Mitigation Plan for each county and municipality describes and summarizes the Committee’s process, findings, and recommendations.
In order to meet the project goals the following objectives were met:
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Application of a planning process that insured a cooperative effort between all interested parties, public and private.
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Identification of the flood hazards and an assessment of the risks associated with those hazards.
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Involvement of the public to create awareness and understanding of local flood hazards and their associated risks and build public support for actions to mitigate those risks.
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Development and evaluation of appropriate mitigation activities to reduce or eliminate the long-term risk of flood damage to buildings, manufactured homes, and other structures insurable under the National Flood Insurance Program (NFIP).
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Development and evaluation of appropriate mitigation activities to reduce or eliminate the long-term risk of flood damage to natural resources.
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Identification and evaluation of alternative incentives and resources available to encourage flood mitigation activities by the affected municipalities.
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Adoption of implementation-ready flood mitigation plans for participating communities and counties.
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Assistance in securing state and federal approval for each of the municipal flood mitigation plans.
The benefits of adopting the Flood Mitigation Plan at the municipal and county level include the following:
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Opportunities for future funding for planning and implementation from state and federal sources.
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Opportunities for communities to participate in the Community Rating System and be eligible for reductions in NFIP premiums.
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Encourages watershed-wide inter-municipal cooperation.
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Ability to coordinate with watershed management planning efforts.
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Flood damage and hazard reduction to property and safety.
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Identify areas where erosion and sediment control projects are appropriate.
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Identification of critical facilities/structures.
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Increased public awareness of risks associated with flooding.
A flood hazard and risk assessment was completed for each community in 2003. General hazards, in the communities along the Tonawanda and Oatka Creeks in Genesee and Wyoming Counties, include structural damage, floodplain development and impervious surfaces, in-stream debris, stream-bank erosion and associated siltation, culvert maintenance and sizing, and issues associated with existing dams.
Several factors related to flooding may cause structural damage. Structures such as homes and businesses may be swept off their foundations and carried downstream by fast-moving flood waters. Structures such as bridges and houses may also be damaged by impacts from debris carried in fast-moving flood waters. Flood waters also erode and undercut stream-banks, threatening foundations of nearby structures. Wood structures that are flooded for long periods of time may develop dry rot as a result of water-logging.
Flood plains and associated wetlands have a critical role in maintaining the overall flow regime in riverine systems. A river overflows into the flood plain when it exceeds bankfull discharge. Vegetation and organic litter, such as fallen leaves and branches, trap precipitation and release the water slowly into streams after a storm event. However, impervious surfaces such as pavement, building roof tops, and other hard surfaces immediately shed the water which falls on them. Rainfall moves more quickly into streams when land is cleared of vegetative cover and organic litter, and when impervious surface increase in a watershed. As this occurs, the frequency and height of floodplain overflow both increases, often significantly affecting land uses in or near the floodplain.
The accumulation of large woody debris in the channels of Tonawanda Creek and Oatka Creek was cited as the single most significant cause of localized flooding in both study areas. Woody debris accumulates in the stream channels mainly due to water flow undercutting the stream bank. Live trees fall into the channel if their root bases are eroded away. Trees with large trunks and root masses partially obstruct flow in the channel, causing more small debris to accumulate around the larger masses. Other sources of woody debris include beaver activity along the banks, and timber harvesting operations that leave small woody debris scattered in a flood prone area.
Siltation is a general term referring to fluvial (river-transported or deposited) sediment. Siltation results when stream banks are eroded and sediments are transported and deposited downstream in the channel. Siltation results when upland areas are farmed, and soil erodes from field surfaces. Other land uses such as timber harvesting, road building and other land development activities cause silt to be deposited in stream channels when it is not properly contained.
Inadequate culvert maintenance and sizing was identified as being an important cause of localized flooding. Problems result when gravel and soil is washed into roadside drainage ditches and deposited in culverts. If culverts are not cleaned regularly, sediment accumulations reduce the capacity of the culvert to carry channel flows during storm events.
Several dams are located within the stream channels of Oatka and Tonawanda Creeks. In some cases there are problems with abandoned, inactive, and/or unmaintainted dams.
The flood mitigation action items presented in each Flood Mitigation Plan are measures that meet the flood mitigation goals. The action items are based on the risk assessment and/or attempt to build upon efforts and projects previously undertaken or currently underway. The action items are divided into six categories: Public Awareness and Information, Preventive Measures, Natural Resource Protection, Property Protection, Structural Measures, Emergency Services.
General flood mitigation action items and recommendations include the following:
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The Flood Mitigation Plan be used as the first phase in the development of a All Hazard Mitigation Plan so that Hazard Mitigation Grant Program funds can be accessed for additional implementation. Each municipality is required to adopt an All-Hazard Mitigation Plan by November 2004.
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The participating municipalities along the Oatka and Tonawanda Creek take advantage of the development of a Flood Mitigation Plan and any subsequent implementation by participating in the Community Rating System and thereby lowering NFIP premiums.
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Every community that participates in the NFIP has a Flood Plain Administrator identified in their local Flood Prevention Ordinance. That person should be trained by attending training sessions provided by the New York State Department of Environmental Conservation (NYSDEC).
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While all municipalities have their floodplains mapped with the exception of Middlebury and a portion of the Town of Stafford, not all municipalities have a detailed base flood elevation mapped. Therefore, all communities should be mapped so that there is a defined base flood elevation (A Zone). If there is no defined base flood elevation an engineer should be used, along with design standards for siting of new development in the floodplain.
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It is recommended that Tonawanda and Oatka Creeks be classified using the Rosgen Stream Classification System. Classification of the creeks, particularly at priority sites identified by this study will provide a means to understand the existing conditions of the stretch of the stream. Based on the classification of the stream, appropriate stream management technologies can be evaluated and recommended for the specific stream type and concern at the location. Additionally, The following streambank mitigation measures are recommended: maintain riparian buffers on stream channels; discourage agricultural practices within 50 to 100 feet of stream; and vegetate and maintain road ditches
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Debris removal should be a high priority for implementation. All communities should work cooperatively with county agencies, Soil and Water Conservation District, NYSDEC, U.S. Army Corps of Engineers (ACE), and neighboring counties and municipalities on inventory and prioritization of sites, permitting issues with NYSDEC and ACE, acquisition of land owner cooperation/partnerships, including easements and development of a mechanism/model for funding debris removal.
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In general all municipalities should consider the impact of impervious surfaces for stormwater management and facilities should be designed accordingly to meet current flood plain and stormwater regulations. An initial recommendation would be to incorporate associated recommendations into municipal local laws and ordinances.
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Culvert maintenance should be a high priority for implementation. This should include an aggressive program of monitoring, cleaning, and partnering with NYSDOT (state and federal roads). Additionally, sizing of culverts associated with private driveways crossing roads or streams should be installed using a hydraulic analysis that is handled by an engineer or qualified professional. Little used and/or abandoned railroads are also a major issue associated with flooding along the Oatka and Tonawanda Creeks. It is recommended that ownership and responsibility be established, existing problems be inventoried, and that owners be involved to make them aware of the problem and, if necessary, enforce drainage laws
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In a few cases dams are failing. In all cases dams need regular inspection and maintenance. The process should include improvement to the existing inventory that would establish ownership and establish which dams could be repaired, removed or replaced where appropriate.
50
West Main Street, Suite 8107
Rochester, New York 14614
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Last Modified: May 02, 2007