Broomes Island Flood Mitigation Plan

Transcription

1 CAtVERT COUNTY Broomes Island Flood Mitigation Plan Purpose and objectives of the plan: Identify flood and inundation issues specific to Broomes Island; Identify options to mitigate flooding and address safety concerns due to flooding; Make recommendations to mitigate flooding on Broomes Island; Make recommendations on mitigation measures, both short and long term, to address potential inundation impacts to Broomes Island; and Serve as a planning tool to address flood issues and emergency preparedness on Broomes Island. 3 Broomes Island Flood Mitigation Plan Participants: Broomes Island residents; Calvert County Department of Community Planning and Building, Environmental Section (ES CPB); Calvert County Department of Public Safety, Emergency Management Division (DPS EMD); Calvert County Department of Public Works (DPW); and State Highway Administration (SHA). 2

2 Broomes Island Flood Mitigation Plan Planning Process Timeline: Public meeting on May 17, 2014; 12 residents attended the meeting; Preparation of the draft plan occurred between July 2014 and December 2015; March 1, 2016 presentation to the BOCC to proceed with public review; March 2016 through May 2016 public participation process and State Clearinghouse review process and incorporation of comments; and October 25, 2016 Joint Public Hearing with the Planning Commission and the BOCC. Broomes Island Flood Mitigation Plan CpUNTY / r.e<eizw, Flood Vulnerability: Second most flood-prone community in the County; 71 structures are flood-vulnerable; Flooding comes from the Patuxent River and Island Creek; Land elevations are generally less than ten feet and where flooding occurs, generally less than six feet; Base flood elevations in the Special Flood Hazard Area (AE Zone) are five and six feet above mean high tide; and Base flood elevations in the High Velocity Flood Hazard Area (VE Zone) are seven feet above mean high tide. 6 3

3 Broomes Island Study Area & 100 Year-Floodplain'.- Elevation 7/ VE Zone Elevation 6/ AE Zone Elevation 5/ AE Zone Limit of Moderate Wave Action Study Area Based on ZIP Code C UNTY erwr Broomes Island Study Area 7 Broomes Island 100-Year Floodplain Broomes Island Flood Mitigation Plan Contributing Factors: Low land elevations; A high water table; Inadequate stormwater management; The building of homes prior to the County's 1984 initial implementation of flood regulations; and Sea level rise and land subsidence. 4

4 Contributing Factors: Low Land Elevations & A High Water Table Broomes Island's land elevation is generally less than ten feet, and flooding occurs at less than six feet. The AE Zone has a base flood elevation (anticipated flood level during a 100-year storm) of five and six feet above mean sea level. The water table is high, sitting just below the surface of storm drain openings under normal circumstances. 9 Contributing Factor: Stormwater Management & Nuisance Flooding Associated with Wetlands Sirr Vietlinds/Marshes Opening to the Patuxent River Broomes Island Road Causeway C UNTY Nuisance flooding occurs during heavy/prolonged rains and high tides. The low areas adjacent to wetlands are particularly prone to flooding. The Broomes Island Causeway floods. Properties on Songbird Lane, Broomes Island Road, and Oyster House Road flood, even during high tides with no rain. :t, r Approsimate location ' of enlverl: not In scale. Broomes Island Wellands/Marshes & Broomes Island Road Causeway Island Road Causeway 5

5 Contributing Factor: Stormwater Management/Culverts Culverts manage stormwater unless there is prolonged/heavy rain. Nuisance flooding is exacerbated by high tides. Eight culverts provide stormwater management to Broomes Island of which seven are maintained by the State Highway Administration or the County. One of the culverts is located on private property on Patuxent Avenue. UNTY Patuxent Avenue Songbird Ian Grapevine -lab Ka' Billows Island Cove Road CalISCW11 Penkert Lane Cr View Road oyster Road -7 of*, itf Ballard Ro rs ROatl# Cuh 01 b., fappro, location) Areas flooding occurs during heat'./prolonged rains and!or high tides ilpireomes island Flood Vulnerability Areas & Stormwater Management 11 lip.r Contributing Factor: Stonnwater Management: Ballard Rogers Road Patuxent River 74K" etta nds Area Al Pa tux eat River Wetlands Where Ballard Rogers Road/Penkert Lane/River View Road converge, tidal waters and stormwater backflow from the pipe on the Patuxent River through Area B and into Area A. Stormwater management of stormwater from County roads is the County's responsibility. :11.- o Approximate location oistorm drains and culvertni not to Ballard Rogers Road/Penkert Lane/River View Road Stormwater Management Conveyance 6

6 Contributing Factor: Homes Built Prior to the Implementation of Floodplain Regulations Many structures were built prior to the adoption of the County's floodplain regulations in In 2011 and 2014, Calvert County adopted new floodplain regulations. CALVE RT C UN TY /,W Over time floodplain regulations have become stricter. For example the law requires: increased elevation of structures (higher freeboard, the required elevation of the first floor above the base flood elevation; elevation of outside A/C units; anchoring of fuel tanks; increased venting requirements, etc. 13 Sea Level Rise Scenarios: 1.3-Foot Increase by 2050 & 3.4-Foot Increase by 2100 Broomes Island, MD Potential 100-Year Floodplain in 2050 with an Anticipated Rise of 1.3 Feet By 2050 sea level is projected to rise by 1.3 feet Areas south of Church Road could be impacted. An estimated 100 structures could be impacted. By 2100 sea level is projected to rise by 3.4 feet Areas south of Ash Hook Road could be impacted., An estimated 196 structures could be impacted. Cho IT h Ito; 1 `'' i*it River Vim Rood' Legend _Cy U NTY ////1/7.4,./..v., / I=Broomes Island Study Area :'.." =Existing 100-year floodplain _Base Flood Elevation Broomes Island Potential 1.3-Feet Increase in the 100-Year Floodplain by Source: Calvert County and DNR's Coastal Atlas 7

7 Wetland Migration by 2050 & 2100 Sea Level Rise Vulnerable Wetlands New Wetland Areas. Year 21 un Ness Wetland Areas III Current Estuarine Open Water Swamp Sea Level Rise Vulnerable Wetlands New Wetland Areas. Year 210u New Wetland Areas Estuarine Open Water 111 Current II Swamp Cypress Swamp Inland Fresh Marsh Cypress Swamp New Wetlands by 2100 circled/dark green 1111 Inland Fresh Marsh (assuming a 3.4-foot inundation increase) (Source: DNR Coastal Atlas) New Wetlands by 2050 circled/orange (assuming a 1.3-foot increase in sea level) 15 (Source: DNR Coastal Atlas) High Tide Vulnerability Currently, high tide tends to flood the properties along Oyster House Road, and even more so after heavy/prolonged rains. CpuNTY 1 7,-../x/ve-../.,- High Tide Vulnerability (Source: DNR Coastal Atlas) 16 8

8 fa. 10/3/2016 Current Storm Surge C. UNTY 1. iii iii ir. Category 1 hurricane events may flood the Broomes Island Road Causeway and the wetlands/marshes along Songbird Lane. Category 2 hurricane surges may flood Patuxent Avenue and Oyster House Road in their entirety. Category 3 and Category 4 hurricanes may flood the bottom two-thirds of the peninsula, generally south of Fish Hook Road to the southern tip, which generally coincides with the 2100 inundation scenario. Category 1 Hurricane: 5-7 feet I u ne: "feet I Category 3 Hurricane: feet I Category 4 Storm: feet Broomes Island Storm Surge Vulnerability (Source: DNR Coastal Atlas) Shoreline Erosion and Rates of Change Broomes Island experiences a slight rate of shoreline change and erosion. Broomes Island Erosion Rate Map (Source: DNR Coastal Atlas) Broomes Island Shoreline Rates of Change Map (Source: DNR Coastal Atlas)18 9

9 Broomes Island Flood Mitigation Plan Residents Ranked Concerns 11 Broomes Island Residents' Flooding Concerns - Ranked #1 Wetland/marsh management is needed during times of heavy rain, tropical storms and high tide. #2 Financial assistance is needed to elevate homes or grade yards to drain water away from homes. #3 Emergency response needs to be addressed at Broomes Island Road Causeway when flooding occurs. Points Given by Residents #4 Flood water on the roads needs to be addressed #5 Water quality is impacted by flooding and needs to be addressed. #6 Hurricanes and emergency preparedness need to be addressed #7 Flooding of businesses needs to be addressed r CALVE RT C. UN TY Broomes Island Flood Mitigation Plan Recommendations Under current conditions, raise 4,368 linear feet of Broomes Island Road and 1,558 linear feet of the Broomes Island Road Causeway by 4.5 feet, for a total of 5,926 linear feet. Funding options will need to be explored (estimated cost $1.5 million). Elevating the Broomes Island Road Causeway by 4.5 feet will alleviate flooding during heavy/prolonged rain events; however, it may not remain dry for more severe 4peori events such as a hurricane or nor'easter. Proposed 4.5 Foot Elevation of 20 Broomes Island Road Causeway 10

10 Broomes Island Flood Mitigation Plan Recommendations Under the scenario of a 1.3-foot sea level rise by 2050, an option is to elevate, demolish structures/acquire property or construct amphibious houses on impacted streets south of School Road. The recommended elevation for structures ranges from 7.9 feet to 10.1 feet. Resting Postion Flood event Ln traernr flroxi the house can rot orer23 meters IS.2 feet) Source: 21 Broomes Island Flood Mitigation Plan Recommendations Under the scenario of a 3.4-foot sea level rise by 2100, an option is to construct a boardwalk system serving structures elevated atop roadways that may be under water in In addition, homes should be elevated 9.1 feet to 13.7 feet and/or amphibious houses could be constructed. Source: Source: amphibious-houses-built-to-survive-thecoming-floods.htmln 22 11

11 --mmonni Broomes Island Flood Mitigation Plan Recommendations Work with the Federal Emergency Management Agency (FEMA) to secure grant funds to elevate structures and/or demolish structures/acquire properties. Conduct a stormwater management study where Ballard Rogers Road, Penkert Lane and River View Road converge. Work with Penkert Lane property owner to address stormwater conveyance issues and failing septic system issues Ensure culverts along Broomes Island Road remain unclogged and debris free. 23 Broomes Island Flood Mitigation Plan Recommendations On Patuxent Avenue, the property owner with the stormwater problem is encouraged to elevate the primary structure and conduct an elevation/drainage study. Where septic systems are failing, apply for Bay Restoration funds to upgrade septic systems. Plant trees in yards - apply for free trees through Calvert County's critical area reforestation program, for the purposes of flood control. Factor sea level rise scenarios into the Broomes Island flood protection elevation requirements

12 Broomes Island Flood - Mitigation Plan Recommend that the Planning Commission make a recommendation to the BOCC to approve the Broomes Island Flood Mitigation Plan. Recommend that the BOCC approve the Broomes Island Flood Mitigation Plan. UNTY 25 Broomes Island Flood Mitigation Plan Questions? Comments?.do Flooding Oyster House Road Flooding at The Point at Broomes Island COUNTY Flooding near the Broomes Island Causeway Jr 13