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dnrec.delaware.gov

Presentation

City of New Castle PresentationDelaware Bay Dikes Repair and Prevention ProjectPreliminary Design for New Castle DikesNew Castle Conservation DistrictDNRECAugust 22, 2012© 2012 O’Brien & Gere


AgendaProject BackgroundProject ObjectivesEngineering InvestigationsNew Castle Dikes Upgrade and RepairComments and QuestionsNext Steps2© 2012 O’Brien & Gere


Project Background Delaware Bay Dikes Repair and Prevention Project Authorized in Senate Bill 130 (FY 20120) - $3M appropriated› Authorized in House Bill 410 (FY 2013) - $2.5M appropriatedto DNREC for “dikes/dams” Priorities for improvements:1. Red Lion Dike2. New Castle City Dikes (from North to South - Buttonwood,Broad Marsh and Gambacorta)3. Army Creek Dike3© 2012 O’Brien & Gere


Engineering Investigations Scope of Engineering Investigations Visual Inspections Geotechnical Investigations Topographic Survey4© 2012 O’Brien & Gere


Engineering InvestigationsSite Location Map – City of New Castle Dikes5© 2012 O’Brien & Gere


Engineering InvestigationsNew Castle Dikes Inspection – Buttonwood Dike6© 2012 O’Brien & Gere


Engineering InvestigationsNew Castle Dikes Inspection – Broad Marsh Dike7© 2012 O’Brien & Gere


Engineering InvestigationsNew Castle Dikes Inspection – Gambacorta Dike8© 2012 O’Brien & Gere


Engineering InvestigationsNew Castle Dikes Geotechnical Investigation9© 2012 O’Brien & Gere


Engineering InvestigationsButtonwood Dike Plan10© 2012 O’Brien & Gere


Engineering InvestigationsButtonwood Dike Profile11© 2012 O’Brien & Gere


Engineering InvestigationsBroad Marsh Dike Plan12© 2012 O’Brien & Gere


Engineering InvestigationsBroad Marsh Dike Profile13© 2012 O’Brien & Gere


Engineering InvestigationsGambacorta Dike Plan14© 2012 O’Brien & Gere


Engineering InvestigationsGambacorta Dike Profile15© 2012 O’Brien & Gere


Engineering InvestigationsDike Elevation Design Criteria16© 2012 O’Brien & Gere


Engineering InvestigationsKey Dike Data from Topographic SurveysDikeApproximateDike Length (FT)Minimum CrestElevation(FT NAVD 88)Length-weightedAverage Elevation(FT NAVD 88)South End of DikeElevation(FT NAVD 88)North End ofDike Elevation(FT NAVD 88)Gambacorta 1,600 6.8 8.2 8.4 8.0Broad Marsh 1,350 5.2 7.8 6.7 8.2Buttonwood 1,800 5.8 7.5 >10.0 >10.0USACE RIP Minimum Elevation – 8.2’17© 2012 O’Brien & Gere


Engineering InvestigationsCity of New Castle – Buttonwood Dike Raising Up to 2.7 FeetRequired (1.0 feetAverage) Unwanted Vegetation18© 2012 O’Brien & Gere


Engineering InvestigationsCity of New Castle – Broad Marsh Dike Raising Up to 3.3 feetRequired (0.7 feetAverage) Extension Required atSouth End Unwanted Vegetation19© 2012 O’Brien & Gere


Engineering InvestigationsCity of New Castle – Gambacorta Dike Raising up to 1.7 FeetRequired Minimal onAverage Extensions Needed atNorth End Flood Side Erosion to beAddressed Unwanted Vegetation20© 2012 O’Brien & Gere


Engineering InvestigationsNew Castle Dike Findings Settlement Revetment Protection Loss Erosion Overtopping Seepage Unwanted Vegetation Tie-out Extensions Required21© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairRecommendations:• Raise Dikes to Elevation 8.5 Feet• Enlarge Dike in Portions (Raising andBroadening)• Supplement/Replace Flood Side Rip Rap• Remove Trees and Woody Vegetation• Construct Filters on Seepage Areas• Extend Dikes to Tie-Out as Required22© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairButtonwood Dike Improvements23© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairBroad Marsh Dike Improvements24© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairGambacorta Dike Improvements25© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairImprovements – All Dikes26© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairBroad Marsh Dike – South Extension27© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairGambacorta Dike – North Extension28© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairNew Castle Dikes Improvements – Estimated Construction CostsTOTAL COSTDescriptionGambacortaDikeBroadMarsh DikeButtonwoodDikeOverall Site Preparation, includes: Clearing/grubbing, common fillfor access roadway, topsoil and pavement strippingFlood (Bay) Side Improvements, includes: Rough grading, earthfill(where required), geotextile, cushion stone layer, riprapProtected (Land) Side Improvements, includes: Rough Grading,replenish riprap, earth fill (where required), geotextile, turfreinforcement matCrest Improvements, includes: Rough grading and compaction,new aggregate surfacing, geotextile, new paving (Gambacortaonly)Site Restoration, includes: Topsoil and seeding, fine-grading ofcrest/roadway, fine-grading of slopes$120,000 $130,000 $120,000$650,000 $570,000 $650,000$190,000 $170,000 $190,000$170,000 $140,000 $150,000$60,000 $60,000 $70,000Subtotal $1,190,000 $1,070,000 $1,180,000Contingency (35%) $420,000 $375,000 $415,000Total $1,610,000 $1,445,000 $1,595,00029© 2012 O’Brien & Gere


New Castle Dikes Upgrade and RepairPermit RequirementsUS Army Corps of Engineers (Section10 and Section 404)DNREC Wetlands and Sub-AqueousLandsNPDES Stormwater DischargeAssociated with Construction ActivityNew Castle County FloodplainNew Castle County Application for PlanReview30© 2012 O’Brien & Gere


Comments and Questions31© 2012 O’Brien & Gere


Next StepsComplete Detailed Design of SelectedDike ImprovementsPrepare and Submit Permit Applicationsfor Selected New Castle DikeAdvertise for Dike ConstructionConstruction of Selected New Castle DikeImprovements32© 2012 O’Brien & Gere


New Castle Conservation DistrictDNREC33© 2012 O’Brien & Gere

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