Agenda - Council - 12/08/2015 - Laserfiche WebLink

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Results Erosion Most of the shoreline inventoried had only limited erosion. About 93% of the shoreline inventoried was rated either slight or moderate erosion (0.0 - 0.2 ft/yr). 3.5% of the shoreline was rated severe (0.3 - 0.5 ft/yr) and another 3.5% was rated very severe (>0.5 ft/yr). Most of the badly eroding shoreline is located on public property. Although only 26% of the shoreline is public property, it contains 59% of the severe erosion and 93% of the very severe erosion. As a result, public land accounts for 78% of the total sediment loss from this section of river. Erosion Summary Erosion Severity Length (miles) % Slight 11.46 70.5% Moderate 3.65 22.5% Severe 0.58 3.5% Very Severe 0.57 3.5% Total 16.26 100% Erosion on Public Land Severe Very Severe Estimated Soil Loss Miles % Miles % Tons/Year 49.1% Public Land 0.34 59% 0.53 93% 4081 78% Private Land 0.23 41% 0.04 7% 1139 22% Shoreline Structures A slim majority of the shoreline had no shoreline structures to protect the bank from erosion (59.4%). Around 20% of the shoreline was protected by a retaining wall, along with another 20% protected by rip rap. Less than 1% of the shoreline was identified as a constructed beach. There was again a large difference between public and private property. Nearly 90% of public land had no shoreline structure whatsoever. This isn't surprising given that most of the public land is park land, but it does help explain why so much of the public shoreline is eroding. 5 Shoreline Structures Summary Structure Type Material Private Public Total None Vegetation/Bare 49.1% 87.8% 59.4% Boulder 10.4% 7.6% Concrete 1.9% 0.1% 1.4% Gabion 0.5% 0.4% Retaining Wall Landscape Block 2.2% 1.6% Rail Road Ties 12.1% 8.9% Sheet Piling 0.5% 0.4% Wood 0.1% 0.0% Subtotal 27.7% 0.1% 20.4% Concrete 0.8% 3.1% 1.4% Rip Rap Rock 21.7% 8.5% 18.2% Subtotal 22.5% 11.6% 19.6% Sand Beach Sand 0.7% 0.4% 0.6% 100.0% 100.0% 100.0%