Small Wonder: Big on Dam Safety

Jeremy Young, PE Dave Twing, PE Jason Arndt, PEMay 13, 2015

Presentation Outline

Evolution of Dam Safety in DE DNREC/DelDOT Partnership DelDOT Dam Prioritization DE Dam Preservation Program Data Review CFD Pilot Project Recommended Modeling Approaches

#49!

1974

First Comprehensive Statewide Inventory by DNREC and University of Delaware

1978-1981

USACE Developed Initial DE NID Dataset

Conducted Phase I Inspections

State Dam Safety Legislation Introduced Never Passed

Dam Safety in DE

In the Beginning…

1998 FEMA NDSP Participation

1999UDWRA Formed

2000DNRECDam Safety Guidance Committee Formed

2000Dam Safety Law Introduced

Dam Safety Rumblings

Law Not Passed Due to Objections from Private Owners

2003 Revised Law Introduced

2004Dam Safety Law Passed!

2006Dam Safety Regulatory Advisory Committee Formed

2009Dam Safety Regulations Adopted!

Back to the Drawing Board

2003Records Pond Upgrading Design

2006 Evaluation of Haven and Silver Lake Dams

1999 Initial Inspections

of 10 High Hazard Dams

2008Update Statewide Inventory of Dams

Let’s Get to Work!Keep up the Good Work!

2009-2012 DNREC Contracts

4 Prime Consultants

42 Dams

Dam Inspections

37 Dams

Bathymetric Surveys

42 Dams

Sunny Day DBAs

11 Dams

H&H/IFAs

Abbotts Pond Dam Griffith Lake Dam

Emergency Dam Repairs

DNREC/DelDOT Partnership

2010

DelDOT began assisting with dam inspections

2011

First MOA between DNREC and DelDOT to share resources

Updated prioritization ranking for state-owned dams

DelDOT Dam Prioritization

Deficiency Point Formula and Index Factors

Deficiency Points

Risk Index Factors (55%)• Dam Characteristics• PAR

Conditional Index Factors (30%)• Physical Condition

Functional Importance Factors (15%)• Road Type• Avg Daily Traffic • Evacuation Route

Deficiency Point Index Factors

Embankment and Spillway

Condition Ratings

Annual Inspection

Spillway Capacity

PAR

Desktop Review/Update

Data Entry/Spreadsheet

Higher Score = Higher RiskResults Ranked

DelDOT Dam Prioritization Process

Planned Upgrading Projects

Hearns Pond Dam

Overtopped 2001/2006

Est. Constr. 2015

Records Pond Dam

High PAR

Est. Constr. 2017

Gated Spillway Improvements

Griffith Lake

Portsville Mill Pond

2013-2014: Program developed through 2nd MOA between DNREC and DelDOT

2014: DelDOT awarded 5-yr contract Evaluate 39 Dams Build upon work completed under 2009 DNREC

Contracts Dam Breach Analyses Incremental Flooding Analyses Inundation Mapping

Dam Preservation Program

2009-2012 DNREC Contracts

4 Prime Consultants

42 Dams

Dam Inspections

37 Dams

Bathymetric Surveys

42 Dams

Sunny Day DBAs

11 Dams

H&H/IFAs

Compiled/ReviewedReports/Data/Models/Etc.

Established 63 Unique H&H Related Fields

Developed Spreadsheet Database

Developed Summary Sheets for Each Dam

Assess Accuracy/Completeness of

Available DataAvoid Duplication of Effort

Critical First Step!

Data Review

Sample Summary Sheet

Sample Summary Sheet

Sample Summary Sheet

Sample Summary Sheet

Sample Summary Sheet

GIS Mapping Tool

Various H&H Models Hydrology: HEC-1 vs. HEC-HMS Spillway Modeling: HEC-1 SS/ST Cards, Rating

Curves, HEC-RAS Dam Breach Modeling: HEC-1 vs. HEC-RAS Flood Routing: HEC-RAS Unsteady

Data Acceptable for FY 2015 Dams

Data Review Findings

DELMARVA Unit Hydrograph Paxson & Welle (2006) Lag Time Method

Challenges with H&H Modeling in DE

Flatland Hydrology

Challenges with H&H Modeling in DE

Weir Submergence

Challenges with H&H Modeling in DE

Spillway Configurations

Challenges with H&H Modeling in DE

Breach Submergence

H&H Analyses – Common Tools

HEC-1

HEC-HMSEmpirical Deterministi

cHEC-RAS

1-DInundation

Map

Water

Hydraulic Structures

Dam Breaks

Coastal

River Hydraulics

Computational Fluid Dynamics

3D CFD Modeling for Spillways

Graphics courtesy of Schnabel Engineering and Flow3D

2D CFD Modeling

More detailed

Consider Breach Submergence

Consider Floodplain Storage

Graphics!!

CFD PILOT PROJECTSilver Lake DamMilford, DE

Silver Lake Dam

Pertinent Data

Silver Lake Dam

Parameter Silver Lake DamDrainage Area 27.8 sq. mi.Top of Dam (uneven) EL 12.8 ft to 13.5 ftMaximum Dam Height 13.5 ftDam Length 550 ftNormal Pool EL 5.9 ftNormal Pool Storage 116 acre-ftNormal Pool Area 32.2 acresTop of Dam (EL 13.0) Pool Storage 474 acre-ftTop of Dam (EL 13.0) Pool Area 59 acres

Sunny Day Breach Analysis (Pool @ TOD)

Spillway Discharge Rating Curve Developed in HEC-RAS/Steady Flow Considering Tailwater Effects

Breach Outflow Hydrograph Developed in HEC-1 and Included Tailwater Rating

Incremental Flooding Assessment Performed in HEC-RAS/Un-Steady Flow

Recommended SDF = 0.2 PMF

Silver Lake Dam

Previous Analyses (2006-2009)

3D CFD Spillway Model (2014)

Silver Lake Dam

3D CFD Results

3D CFD Results

Silver Lake Dam

CFD Model Estimated Higher Spillway Capacity than 2009 HEC-RAS

Spillway Modeled as XS, Inline Structures, Bridges in HEC-RAS

Interpolations between XS in HEC-RAS

Challenges Numerically Solving HEC-RAS Model

Different Equations Simulating the Flow

And Computing Tailwater Submergence

Differences in Spillway Ratings May Be Due To…

Silver Lake Dam

Variety of Acceptable Tools for Developing Spillway Ratings

Need Good Engineering Judgement and Understanding of Spillway

3D CFD Can Confirm Previously Developed Spillway Ratings

Particularly for Spillways Subject to Tailwater and Close to Bridges

Refinement of Spillway Rating May Reduce/Eliminate Costly Rehabs

3D CFD Conclusions

Silver Lake Dam

Dam Breach Modeling

Silver Lake Dam

Scenario AnalysisStarting Pool EL

(ft)

Peak Flow(cfs)

Peak Reservoir Elevation

(ft)

Inflow Outflow

0.2 PMF – Breach2009 HEC-1 5.9 4,710 7,170 15.5

2014 HEC-RAS 5.9 4,710 4,790 13.4• 2009 Analysis is conservative • Higher peak outflow computed by HEC-1 would produce a

larger inundation area• HEC-1 (emprical methods) has been superceded by HEC-

RAS (flood routing)

Flow-3D (Shallow Water Module)

GIS Data, Surveys, Site Plans

1.2M Cells/10-ft Grid

Scenarios

0.2 PMF No Breach

0.2 PMF Breach

Sunny Day Breach

Silver Lake Dam

2D CFD Flood Routing

More Detailed Results (vs. HEC-RAS)

More Robust Analysis (vs. Interpolated HEC-RAS XS)

Computed 0 to -3-ft Difference Depth (vs. HEC-RAS)

Smaller Inundation Areas

Longer Computation Time

May Not Be Appropriate/Efficient for IFAs

Could be Used to Refine Inundation Analysis to Better Define Hazards

Silver Lake Dam

2D CFD Results

Silver Lake Dam

Moving Forward - Update Previous Analysis

Model Dam Breach in HEC-RAS

‘Calibrate’ HEC-RAS Spillway Model to 3D CFD

Update IFA in HEC-RAS/Unsteady and Recommend New SDF

Depending on Results, Run 2D CFD for New SDF

Update Maps with Either HEC-RAS or CFD Result

Consider 3D CFD to Model Spillways Subject to Tailwater and Close to Bridges

Develop Breach Outflow Hydrograph in HEC-RAS

Perform Initial IFA with HEC-RAS/Unsteady

Consider 2D CFD for IFA on Case by Case Basis

Consider 2D CFD to Refine Inundation Limits and Estimate Potential Hazards

Recommended Modeling Approaches for Future Studies in DE

Questions/Comments?