1. THE IMPORTANCE OF REAL-TIME DATA DURING AN OPERATIONAL RIVER FLOOD EVENT Ronald Horwood National Weather Service Northeast River Forecast Center Taunton MA NROW 2004

2. INTRODUCTION Synoptic Overview Pawtuxet River Basin Characteristics NWSRFS Basics Operational Forecasts Conclusions

3. SYNOPTIC OVERVIEW From 13-14 April 2004…low pressure moved northeast from the southern Appalachians passing south of New England. Storm total rainfall of 2 to 5 inches occurred across southeastern New England and eastern Long Island in New York State This resulted in significant flooding across the Pawtuxet River Basin in Rhode Island

4. H50 and MSLP – 13 April 2004 – 12z

5. H50 and MSLP – 14 April 2004 – 12z

7. THE PAWTUXET RIVER BASIN Roughly 200 square miles draining a large portion of northern Rhode Island. Approximately the northern ½ of this basin is controlled by Scituate Reservoir (the city of Providence’s drinking supply) The southern ½ of the basin including the NERFC forecast point at Cranston is heavily urbanized and relatively uncontrolled.

8. PAWTUXET BASIN - cont Scituate Reservoir levels are critical for forecasting downstream at the NERFC forecast point at Cranston on the Pawtuxet River. –If Scituate reservoir is not spilling, roughly ½ of the runoff is contained, thus reducing river flow at Cranston. –If Scituate reservoir is high enough to be spilling, an uncontrolled flow of water will be routed down to Cranston. When added to the local urban runoff, uncontrolled discharge from Scituate reservoir can lead to significant flooding along the Pawtuxet River. –The NERFC obtains Scituate Reservoir levels and discharges via a public web page.

9. THE PAWTUXET RIVER BASIN

11. NERFC FORECAST OPERATIONS NERFC forecasters use the National Weather Service River Forecast System (NWSRFS) to forecast river stages for more than 100 forecast points across New England and New York State. –The model is sensitive to a number of variables including but not limited to rainfall, snowmelt, vegetation type and coverage and soil moisture.

12. PAWTUXET RIVER FORECASTING For the NERFC forecast point at Cranston (CRAR1), the flow routed from Scituate Reservoir is added to the local runoff to give a total runoff hydrograph at CRAR1. Again, if Scituate reservoir is not spilling, roughly ½ of the runoff is contained and will not reach Cranston making it very difficult to flood. If Scituate reservoir is spilling, however, additional uncontrolled flow is added to a very urbanized basin making significant flooding much more likely. RAINFALL LOCAL RUNOFF VOLUME OF WATER AT CRANSTON SCITUATE OUTFLOW

13. THE EVENT During the morning of 14 April 2004…the NERFC forecasts called for minor flooding on the Pawtuxet River at Cranston with a maximum forecast stage of 9.8 feet. (Flood Stage = 9 feet) –This was based on a couple of factors: Most of the rainfall had already occurred. Data from the Scituate Reservoir indicated the reservoir was still a touch below spillway so NERFC forecasters believed there was little in the way of uncontrolled flow making its way into the Pawtuxet River from the reservoir.

14. AM Forecast – 14 April 2004

15. THE EVENT - cont By late morning and early afternoon on the 14 th …it was apparent the Pawtuxet River was rising much faster than forecast.

16. THE EVENT – cont NERFC forecasters believed there was too much volume reaching Cranston with Scituate Reservoir near or just below spillway elevation so an “on the fly” field trip to Scituate Reservoir was taken. –Upon arrival at Scituate Reservoir, it was readily apparent there was a lot of water spilling from the reservoir and that the morning web page data was incorrect.

17. SCITUATE RESERVOIR – APPROXIMATELY 3 PM EDT – 14 APRIL 2004

18. THE EVENT - cont By this point…the NERFC was in catchup mode and issued 2 additional forecasts basically chasing the rising stages. However…upon returning to the forecast office…NERFC forecasters were able to better simulate the flow out of Scituate Reservoir to produce a much more realistic forecast depicting moderate flooding at the Cranston forecast point.

19. SIMULATED FORECAST INCORPORATING SCITUATE RESERVOIR OUTFLOW

20. RESULTS The Pawtuxet River crested at 11.8 feet…more than 2.5 feet over flood stage and 2 feet above the NERFC forecasted crest from the morning of 14 April 2004. –This resulted in moderate flood levels along the Pawtuxet River which ended up closing roads and flooding out businesses. –The poor morning forecasts were directly attributable to bad data on the publicly accessed web page the NERFC uses to estimate outflow from Scituate Reservoir.

21. FORECAST COMPARISON Operational Forecast with bad data from website (Scituate Reservoir not spilling) Simulated Forecast with estimated outflow (from field trip or good data from website)

22. CONCLUSIONS/SUGGESTIONS It is vital for river forecast operations to have a reliable source of real-time data. –In this instance…a publicly accessed web site was not sufficient and resulted in bad flow data being incorporated into NERFC river models. This resulted in little to no lead time for businesses along the Pawtuxet River that they would indeed be impacted by high water since NERFC forecasters were for the most part chasing the forecast. –Until NERFC forecasters knew what was happening at Scituate Reservoir…they believed the reservoir to be below spillway elevation.

23. CONCLUSIONS/SUGGESTIONS Better coordination is necessary between WFOs and RFCs to ensure the data link is not broken. –Perhaps problem flood spots should be upgraded to satellite telemetry to ensure more reliable data feeds. –More outreach is needed to foster better working relationships between private water supply operators and the NWS. In this case…we had no way of getting reliable flow data for Scituate Reservoir once the web page went down.

24. QUESTIONS/COMMENTS ?