1OO-YEAR FLOOD Due to the lack of periodic maintenance dredging, significant shoaling has occurred within the 3-mile long Flood Risk Management Channel since the construction of the inlet. The hydraulic analysis report1 by the Army Corp of Engineers (ACE) identifies that; the existing condition of accumulated sedimentation has reduced 70 percent of the flood channel’s capacity to contain a 100-year flood. Under this current condition, the number of properties falling within the revised flood boundaries has increased by 44 percent, encompassing buildings not constructed to meet flood elevation standards for the 100-year flood zone.

1 US Army Corps of Engineers, Buffalo District (2011). Hydraulic Analysis and Impact of Long Term Shoaling for Flood Risk Management Project, Cayuga

PROPERTIES TO BE AFFECTED Total property damages, for the three dredging scenarios proposed are analyzed below: If existing flood channel conditions are maintained:

Total Properties Affected = 899 𝐑𝐞𝐬𝐢𝐝𝐞𝐧𝐭𝐢𝐚𝐥 = 𝟒𝟗𝟒 𝐂𝐨𝐦𝐦𝐞𝐫𝐜𝐢𝐚𝐥 = 𝟑𝟎𝟖

Total Property Value= $420,725,201 Residential Property Value= $68,840,000 Commercial Property Value= $245,357,300

With the above baseline figures, the cost benefit effects of the proposed dredging alternatives can then be identified. Alternative 1:- Lower Channel Dredging Dredging is limited to the lower portion of the channel to reduce flooding along the Cayuga Inlet. Expected reduction will occur around the floodplain areas of

• Fall Creek • Cascadilla Creek and the

• Lower Channel of Cayuga Inlet

Total Properties Affected= 541 𝐑𝐞𝐬 = 𝟐𝟐𝟏 𝐂𝐨𝐦𝐦 = 𝟐𝟎𝟕

(40.5% reduction in number of affected properties)

Property Value=$332,305,201 Residential Property Value=$27,760,000 Commercial Property Value=$222,675,300

PROPERTY TAX ASSESMENT 100 & 500 YEAR FLOOD ZONES

Prepared by: Elizabeth Agyeman-Budu

City of Ithaca

1981 FEMA Measured Flood Boundary

(623 properties affected)

2011Army Corps Measured Flood Boundary (899 properties affected)

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Alternative 2:- Lower & Middle Channel Dredging Dredging is limited to only the lower and middle portions of the flood channel. Reduces the number of properties affected along: • Fall Creek • Cascadilla Creek • Lower & Middle Channel of the Cayuga inlet • Some properties along Six Mile Creek

Total Properties Affected= 276 𝐑𝐞𝐬 = 𝟗𝟑 𝐂𝐨𝐦𝐦 = 𝟏𝟎𝟕

(69.7% reduction in the total number of affected properties) Property Value=$260,267,909 Residential Property Value=$11,810,000 Commercial Property Value=$170,978,300 Alternative 3:- Complete Channel Dredging Under this alternative, the entire flood channel (including Old Cayuga inlet and Six mile Creek) is dredged to its original design specifications. Flooding will largely be contained within the flood channel with minor over toppings in the areas lying between the right bank of the Cayuga inlet and the railroad. The number of affected properties is reduced by an estimated 95 percent.

500-YEAR FLOOD The 500-year flood data is not as up-to-date as the 100-year flood data. Therefore under the existing conditions of the flood channel, documented flood boundaries may have extended, with more properties being affected than the estimates being presented.

PROPERTIES AFFECTED

Total Properties Affected =1667 𝐑𝐞𝐬 = 𝟏𝟐𝟎𝟖𝐂𝐨𝐦𝐦 = 𝟐𝟖𝟔

Total Property Value= $561,911,131 Residential Property Value= $207,484,000 Commercial Property Value= $174,498,000 2

TOTAL PHYSICAL PROPERTY DAMAGE Under the existing flood channel conditions, a 100-year flood event can have a flooding depth ranging between 0 to 10 feet, has the potential of damaging $421 million worth of property and displacing an estimated number of 610 families. The City Government could also incur a loss of $37 million worth of city owned property damage. In the case of a 500-year flood event, there is an estimated $62 million worth of property damage. Even though the percentage damage in both flood events is highest among private owned property within the city, the municipal government is also at risk of incurring an estimated $37 million worth of damage in a 100-year flood event and a $29 million worth of damage in a 500-year event3 to city owned property. Given the current condition of the flood channel, the city is advised to start dredging to reduce the potential damage to lives and properties within the city. The city is also recommended to revise and update its 500-year flood data to reflect the existing conditions of the flood channel.

REFERENCES

1. US Army Corps of Engineers, Buffalo District (2011). Hydraulic Analysis and Impact of Long Term Shoaling for Flood Risk Management Project, Cayuga Inlet, Ithaca, New York

2. 2013 Parcel Shapefile, Department of Public Works—GIS Program, City of Ithaca

3. 2013 Parcel Shapefile, Cornell University Geospatial Information Repository

4. 2013 Property and Land Value Data. Tompkins County Assessment Office

2 Estimates are based on the 1981 FEMA 500-year flood data. However under the current conditions of the flood channel, the estimated damages could increase up to 44 percent 3 The 500-year flood estimate is expected to go up if existing conditions of the flood channel is taken into account

1981 FEMA 500-Year Flood Boundary

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