Forecasting the September 2016 Flood in the Cedar River Basin

Transcription

1 Forecasting the September 2016 Flood in the Cedar River Basin 55th Annual ASCE Environmental Design and Water Resources Conference Cedar Rapids, Iowa Brian Connelly Senior Hydrologic Forecaster NOAA/NWS

2 Outline Introduce NWS Hydrology Program Describe September, 2016 event Forecasting challenges Shell Rock River Importance of coordination

3 NWS Mission Provide weather, water, and climate data, forecasts and warnings for the protection of life and property and enhancement of the national economy Specific Goal 2011 NWS Strategic Plan: Deliver a broad suite of improved water forecasting services to support management of the Nation s water supply.

4 NWS River Forecast Centers

5 Community Hydrologic Prediction System (CHPS) Any other model

6 Cedar River Basin 27 Sub-basins; 16 Forecast points

7 24-hr Rainfall Ending 1pm September 22 Cedar Falls Cedar Rapids

8 Precipitation Frequency Shell Rock, IA

9 Antecedent Conditions

10 USGS Flow Time Series Shell Rock River

11 Historical Context n th Highest Stage Crest

12 Shell Rock River at Shell Rock, IA Forecasting Challenges Forecast precipitation Spatial distribution of rainfall Runoff sensitivity Seasonal routing variation Rating Curve Issues o Tributary backwater o Low Steel o Vegetation Photo courtesy of the USGS

13 Shell Rock River at Shell Rock, IA Model Adjustments Rating Curve Issues QPF

14 24-hr Rainfall Ending 1pm September 22 QPF 9/21/16 Radar Rainfall Estimate

15 Shell Rock River at Shell Rock, IA Initial Simulation USGS Peak Flow

16 24-hr Rainfall Ending 1pm September 22

17 Shell Rock River at Shell Rock, IA Adjust Hydrograph Timing

18 Shell Rock River at Shell Rock, IA Lower Runoff Rates by 20% USGS Peak Flow

19 Shell Rock River at Shell Rock, IA Model Adjustments

20 Shell Rock River at Shell Rock, IA Negative Rating Shift ft shift USGS Peak Flow

21 Shell Rock River at Shell Rock, IA USGS Measurement

22 Shell Rock River at Shell Rock, IA USGS Measurement Sep, 2016 Jun, 2008

23 Number of Annual Peaks Negative Rating Shifts Annual Peak Distribution 25 Cedar River at Waterloo, IA 20 Previous annual peaks in the Fall highest was 40% of the flow measured in More Month

24 Negative Rating Shifts Monthly Composite NDVI March, 2009 April, 2009 May, 2009 June, 2009 September, 2009

25 Negative Rating Shifts Bridge Effects Downstream side of bridge in Shell Rock, IA Upstream side of bridge in Shell Rock, IA Photos courtesy of the USGS

26 Negative Rating Shifts Backwater from Confluence -2.8 ft -2.5 ft

27 Other Negative Shifts -0.8 ft -2.8 ft -2.5 ft -0.6 ft -0.4 ft

28 Cedar River at Cedar Falls, IA

29 Cedar River at Cedar Rapids, IA Routing Differences Routings slower and more attenuation due to vegetation.

30 Cedar River at Cedar Rapids, IA

31 Coordination Real-time coordination Enhanced river gage network Collaboration on forecast for Cedar Bluff

32 Summary Every flood is different. The Cedar River Flood of 2016 was a challenge because it was the first flood of it s magnitude on record that occurred during the Fall season. Our models had never been tested against such an event, so there was even more forecast uncertainty than usual. Real-time coordination with partners facilitated forecast updates as data was collected Photo courtesy of the USGS

33 Questions? Forecasting the September 2016 Flood in the Cedar River Basin Brian Connelly Senior Hydrologic Forecaster NOAA/NWS