STONE OAK DAM: TO BREACH OR NOT TO BREACH, THAT IS THE QUESTION. TFMA Spring Conference 2013

Transcription

1 STONE OAK DAM: TO BREACH OR NOT TO BREACH, THAT IS THE QUESTION TFMA Spring Conference May 23, 2013T F M A Spring Conference 2013

2 INTRODUCTIONS ALYSHA GIRARD, P.E., CFM Storm Water Program Manager City of Round Rock RYAN BEARDMORE, CFM Storm Water Program City of Round Rock KIM PATAK, P.E., CFM, CPESC Freese and Nichols, Inc. Project Engineer

3 OVERVIEW Tropical Storm Hermine TCEQ Dam Safety Rules and Regulations Size Classification Hazard Classification Design Alternatives Evaluation Final Design Recommendation Design and Construction

4 TROPICAL STORM HERMINE

5 BACKGROUND T F M A S p r i n g C o n f e r e n c e 2013

6 NWS RADAR COUNTY RAINFALL ESTIMATES T F M A S p r i n g C o n f e r e n c e 2013

7 RAINFALL DATA FROM UBC WCID GAUGES Rainfall Total (inches) Dam MAX 12 hr hr Rainfall Intensity (inches/hr) 1/4 Hr hr

8 DEPTH-DURATION FREQUENCY OF PRECIPITATION NonStorm Event Exceedance (Return Period) Probability Storm Duration (hours) % % % % % % % % % PMF Values in the table represent regional parameters near the center of the District. Values will vary slightly across the District

9 EROSION IDENTIFIED

10 STATE OF FACILITY

11 TCEQ DAM SAFETY RULES AND REGULATIONS

12 DAM SIZE M i n i m u m D a m H e i g hts Intermediate S I Z E C L A S S I F I C A T I O N Category Small Impoundment Maximum Storage (Acre-feet) 15 and < 1, and < 1,000 Height (Feet) 25 and < 40 6 and less than 40 Intermediate 1,000 and < 50, and < 100 Large 50, T F M A S p r i n g C o n f e r e n c e 2013

13 HAZARD CLASSIFICATION

14 DESIGN FLOOD DETERMINATION HAZARD (relating to Hazard Classification Criteria) Low Significant High Hydrologic Criteria for Dams C L A S S I F I C A T I O N SIZE (relating to Size Classification Criteria) Small Intermediate Large Small Intermediate Large Small Intermediate Large MINIMUM DESIGN FLOOD HYDROGRAPH (expressed as a percentage of the PMF) 25% PMF 25% PMF 50% PMF 50% PMF 75% PMF 50% PMF 50% PMF 75% PMF 75% to 100% PMF 75% PMF 75% to 100% PMF 100% PMF When a range is given, the minimum flood hydrograph must be determined by straight-line interpolation within the given range. Interpolation must be based on either height of dam or maximum storage capacity, whichever results in the highest percentage of PMF. The interpolation for large, low-hazard dams for height must be between end points of 100 feet and 50% PMF and 200 feet and 75% PMF. The interpolation for large, low-hazard dams for maximum storage capacity must be between the end points of 50,000 acre-feet and 50% PMF and 30,000 acre-feet and 75% PMF. The interpolation for large, significant-hazard dams for maximum storage capacity must be between end points of 50,000 acre-feet and 75% PMF and 300,000 acre-feet and PMF. T F M A S p r i n g C o n f e r e n c e 2013

15 DESIGN ALTERNATIVES EVALUATION

16 DESIGN ALTERNATIVES REHABILITATION DECOMMISSION Full Partial T F M A S p r i n g C o n f e r e n c e 2013

17 ALTERNATIVE IMPACTS REHABILITATION DECOMMISSION PROS CONS PROS CONS Maintain Flood Detention Water Quality Lifetime Maintenance More Expensive Municipal Liability Public Safety No Woody Vegetation Lifetime Inspections Return Stream Bank Back to Natural Flow Regime Declassify the Dam Less Expensive Lose Flood Storage Potential Mitigation Requirement T F M A S p r i n g C o n f e r e n c e 2013

18 REHABILITATION $317,000 T F M A S p r i n g C o n f e r e n c e 2013

19 FULL DECOMMISSION $229,000

20 PARTIAL DECOMMISSION $135,000

21 PARTIAL DECOMMISSION Hydrologic Design Point 1% Ult Peak Q (cfs) Existing Partial Decom. Flow DS of Stone Oak Dam Confluence with OB Trib % 1,225 1,403 13% FM ,061 1,145 7% Confluence with OB Trib 3 1,362 1,518 9% T F M A S p r i n g C o n f e r e n c e 2013

22 PARTIAL DECOMMISSION T F M A S p r i n g C o n f e r e n c e 2013

23 FINAL DESIGN RECOMMENDATION

24 DESIGN RECOMMENDATION REHABILITATION DECOMMISSION Full Partial Costs $317,000 $229,000 $135,000 Pros Flood Detention Declassify Dam Declassify Dam Cons Lifetime Maintenance Lose Flood Storage Lose Flood Storage Decision Points High Risk Status Downstream Culvert Watershed Maturity Modeling Confidence Watershed Maturity Modeling Confidence Unknown and Timing Haul-off Costs Least Disruption T F M A S p r i n g C o n f e r e n c e 2013

25 DESIGN AND CONSTRUCTION

26 PARTIAL DECOMMISSION FINAL DESIGN Contractor s Low Bid Price: $101,000

27 POST-CONSTRUCTION

28 Q UESTIONS? ALYSHA GIRARD, P.E., CFM RYAN BEARDMORE, CFM 2008 Enterprise Dr. Round Rock, Texas KIM PATAK, P.E., CFM, CPESC Jollyville Road Bldg. 4, Ste. 100 Austin, Texas