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Impact of Recent Flood Events on Peak Discharge Estimates of New Jersey Streams

Impact of Recent Flood Events on Peak Discharge Estimates of New Jersey Streams. Presented by Siva Sangameswaran, Ph D, P E, CFM Venkata Dinakar Nimmala, CFM. Overview. USGS Literature Recent Floods Updated Analysis Summary of Findings. Flood Frequency Estimates.

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Impact of Recent Flood Events on Peak Discharge Estimates of New Jersey Streams

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  1. Impact of Recent Flood Events on Peak Discharge Estimates of New Jersey Streams Presented by Siva Sangameswaran, Ph D, P E, CFM Venkata Dinakar Nimmala, CFM

  2. Overview USGS Literature Recent Floods Updated Analysis Summary of Findings

  3. Flood Frequency Estimates • Flood Frequency Basics • Probability (%) that a Flood will Occur in a Given Year • Flood Insurance Studies – 10% , 2%, 1%, and 0.2% • Estimation Methods • Watershed Model • LP III Analysis • Statistical Analysis of Annual Peak Flows • Bulletin 17B Procedures (USGS) – Log Pearson Type III Distribution • State-wide Regression Equations – Flood Frequency related to Basin Characteristics

  4. Purpose of Study • NJ USGS SIR 2009-5167 Published in May 2010 • Includes Water Year 2007 ( till September 30, 2007) • Recent Flood Event’s Impact on Flood Frequency: • Stream Data Analyzed Statistically • 1% Chance Discharge Affected by Highest Recorded Peak • Regression Equations Aspects • Recent (Post-2007) Rainfall Events in NJ: • Hurricane Bill • Hurricane Earl • Tropical Storm Nicole • Hurricane Irene • Hurricane Lee

  5. HURRICANE IRENE 5” to 10” Rain Across NJ

  6. Impacts of Hurricane Irene in New Jersey Source: NOAA USD $18.7B Damage (USD $1B in New Jersey) Landfall on S. Jersey Shore (Little Egg Harbor) Record Rainfall – Statewide Maximum 11.27” Eleven Rivers Reached Record Levels Transportation Infrastructure Damaged Jersey City, Hoboken (Hudson River) ~ 5 ft Flooding Ten Flooding Related Deaths

  7. Asbury Park, NJ Wind Speeds – 75 mph Massive Street Flooding Raritan River Bridge

  8. Residences and Businesses Flooded Peddie Lake Flooding in Hightstown, NJ Transportation Infrastructure Damage Passaic River Flooding in Patterson, NJ

  9. USGS Stream Gages in New Jersey • 128 Active Gages in NJ • Includes Riverine and • Coastal Channel Gages • SIR 2009 5167 • Included 254 (NY, NJ, PA)

  10. Analysis Methodology • Identify Gages with New Peaks (Post 2007) • Incorporate New Peaks for Gages Studied in SIR 2009-5167 • Rerun PeakFQ using Appropriate Station Skews • Analyze Impacts of New Peaks on Discharges

  11. Streamflow-gaging Stations with > 25 Years of Record Used for Skew StudySource: SIR 2009-5167

  12. Results

  13. Gages with Discharge Increases Fifteen Gages Maximum Increase (104.44%) at 01395000 (Rahway River at Rahway, NJ) Minimum Increase (0.08%) at 01410000 (Oswego River at Harrisville, NJ)

  14. Gages with Discharge Decreases Thirty Gages Maximum Decrease (60.41%) at 01411456 (Little Ease RN near Clayton, NJ) Minimum Increase (2.09%) at 01445500 (Oswego River at Harrisville, NJ)

  15. Discharge Increase Summary

  16. Discharge Decrease Summary

  17. Conclusions New Peaks Recorded at Gages since SIR 2009 5167 Discharge Changes (Increase & Decrease) Observed Hurricane Irene caused changes in Discharges in Northern and central Gages Evaluate Suitability of Regression Equations Modify Approaches if Regression Estimate is Unsuitable

  18. Questions

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