Storm Report : July 31, 2007 Northeast Maricopa County, AZ Stephen D. Waters, Engineering Division, Flood Warning Branch TABLE OF CONTENTS Meteorology ......................................................................... 2 Precipitation......................................................................... 3 Runoff .................................................................................. 7 Thoughts ............................................................................ 11 TABLES Table 1 Table 2 Table 3 15-minute rainfall values at four stations ............................ 5 NOAA 14 statistics for Stagecoach Wash ............................. 6 NOAA 14 statistics for Carefree Ranch ................................ 6 FIGURES Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure I II III IV V VI VII VIII IX X Visible Satellite Photo taken 7/31/07-16:46 MST ................. 2 NE County 24-hr rainfall values from ALERT Stations ........... 3 Radar-estimated rainfall map, Cave Creek area .................. 4 Storm hydrograph, gage 4863 – Rawhide Wash................... 8 Storm hydrograph, gage 4823 – Cave Cr. @ Spur Cross ....... 8 Storm hydrograph, gage 4889 – Cave Creek ....................... 9 Storm hydrograph, gage 4918 – Cave Cr. near Cave Cr. ....... 9 Inflow hydrograph, gage 4899 – Cave Buttes Dam..............10 Storm hydrograph, 09511300 – Verde R. nr Scottsdale .......10 Radar-estimated rainfall map, Cave Creek area ..................11 A special thank you to members of the NWS, USGS and Johns Hopkins University for supplying several of the above figures. Storm Report, July 31, 2007; Page 1 METEOROLOGY July 31, 2007 began as a relatively cloudless day, but signs in the atmosphere were pointing to the potential for unusual storms. Mid-level steering winds were out of the northeast, favoring propagation of mountain storms off the Mogollon Rim into the central deserts. The 5:00 AM KSRP sounding showed that moisture values were high – 1.96 inches of precipitable water, a mean RH of 68% and a surface dewpoint of 65 degrees. Instability values were only moderate (CAPE of 378 J/kg), but appear from later soundings to have increased as the day went on. Figure I below is a visible satellite photo from 7/31/07 at 4:46 PM MST, and clearly shows the line of storms coming off the Rim toward the Phoenix area. Figure I Storm Report, July 31, 2007; Page 2 PRECIPITATION Figure II Figure II – 24 hour precipitation values in the northeast County ending 08/01/2007 at 05:00 MST. All readings are in inches and are from automated Flood Control District rain gages. Storm Report, July 31, 2007; Page 3 Figure III Figure III – this map was generated using GIS and a gridded rainfall product provided by our weather vendor. The colored cells are approximately 1 km on a side and represent an average rainfall depth for that area. The depths are accumulated for the 24-hour period prior to 8/01/2007 at 5:00 AM MST. The cells are derived from an algorithm that accumulates the weather radar returns, then adjusts them using the raingage readings which are shown on this map in black next to the gage locations (black dots). Storm Report, July 31, 2007; Page 4 TABLE 1 DeviceID StatType DataType Units 07/31/07 2300 2245 2230 2215 2200 2145 2130 2115 2100 2045 2030 2015 2000 1945 1930 1915 1900 1845 1830 1815 1800 1745 1730 1715 TOTALS: 4910 rain precip in 4930 rain precip in 5940 rain precip in 4920 rain precip in 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.04 0.00 0.04 0.00 0.00 0.16 0.43 0.55 0.94 0.47 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.04 0.08 0.00 0.00 0.08 0.35 0.59 0.63 0.47 0.24 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.04 0.04 0.04 0.00 0.00 0.08 0.00 0.12 0.43 0.83 0.31 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.24 0.20 0.08 0.24 0.24 0.08 0.00 0.00 0.00 2.68 2.56 1.93 1.18 Device ID 4910 4930 5940 4920 is is is is Stagecoach Wash Carefree Ranch Rackensack Canyon Cave Cr. at Spur Cross Table 1 above presents 15-minute rainfall values at four stations in the watersheds east of Cave Creek. These four gages are close to or within the heavy rainfall area in the middle of Figure III. Their Table 1 totals can be matched to those on the map. Storm Report, July 31, 2007; Page 5 Table 2 below is the NOAA Atlas 14 Point Precipitation Frequency Estimate Table at the latitude/longitude of the Stagecoach Wash raingage. The red line lists the recorded values from Stagecoach Wash on 7/31/07. The blue (last) line is the interpolated return period for each rainfall amount in years. Precipitation Frequency Estimates (inches) 33.8119N 111.8911W AEP* 5 10 15 30 60 120 (1min min min min min min in-Y) 3 hr 6 hr 12 hr 24 hr 48 hr 4 day 7 day 10 day 20 day 30 day 45 day 60 day 2 0.28 0.43 0.54 0.72 0.90 1.03 1.10 1.28 1.54 1.74 2.05 2.28 2.63 2.89 3.73 4.47 5.33 5.95 5 0.41 0.63 0.78 1.05 1.30 1.48 1.54 1.76 2.08 2.47 2.92 3.28 3.79 4.16 5.33 6.39 7.61 8.43 10 0.50 0.77 0.95 1.28 1.58 1.79 1.86 2.09 2.46 3.01 3.55 4.03 4.67 5.11 6.48 7.73 9.19 10.13 25 0.62 0.94 1.16 1.57 1.94 2.19 2.28 2.52 2.94 3.74 4.41 5.09 5.92 6.45 8.04 9.50 11.29 12.35 50 0.70 1.07 1.33 1.79 2.21 2.49 2.60 2.85 3.31 4.34 5.10 5.96 6.95 7.57 9.28 10.90 12.92 14.05 100 0.79 1.20 1.49 2.00 2.48 2.80 2.94 3.20 3.68 4.97 5.83 6.91 8.08 8.77 10.59 12.34 14.60 15.78 200 0.87 1.33 1.65 2.22 2.75 3.10 3.29 3.55 4.05 5.65 6.60 7.93 9.33 10.10 11.99 13.83 16.35 17.56 500 0.99 1.50 1.87 2.51 3.11 3.52 3.77 4.01 4.54 6.63 7.70 9.44 11.17 12.04 13.96 15.91 18.77 19.99 1000 1.08 1.64 2.04 2.74 3.40 3.85 4.16 4.38 4.92 7.44 8.59 10.70 12.73 13.68 15.56 17.57 20.70 21.91 4910 0.59 0.94 1.10 1.65 2.44 2.60 2.68 ≈AEP 21 25 21 34 93 68 62 Table 3 below is the NOAA Atlas 14 Point Precipitation Frequency Estimate Table at the latitude/longitude of the Carefree Ranch raingage. The red line lists the recorded values from Carefree Ranch on 7/31/07. The blue (last) line is the interpolated return period for each rainfall amount in years. Precipitation Frequency Estimates (inches) 33.8530N 111.8644W AEP* 5 10 15 30 60 120 (1min min min min min min in-Y) 3 hr 6 hr 12 hr 24 hr 48 hr 4 day 7 day 10 day 20 day 30 day 45 day 60 day 2 0.30 0.46 0.57 0.76 0.95 1.09 1.16 1.35 1.64 1.96 2.31 2.63 3.04 3.35 4.35 5.20 6.23 7.02 5 0.44 0.67 0.83 1.11 1.38 1.56 1.63 1.85 2.22 2.77 3.30 3.81 4.42 4.85 6.24 7.46 8.94 10.01 10 0.53 0.81 1.00 1.35 1.67 1.88 1.96 2.20 2.62 3.36 4.03 4.69 5.46 5.96 7.59 9.05 10.82 12.05 25 0.65 0.99 1.22 1.65 2.04 2.30 2.40 2.65 3.14 4.17 5.01 5.94 6.93 7.54 9.41 11.16 13.31 14.71 50 0.74 1.12 1.39 1.87 2.32 2.62 2.74 3.00 3.53 4.83 5.80 6.95 8.15 8.84 10.86 12.81 15.26 16.74 100 0.83 1.26 1.56 2.10 2.60 2.94 3.09 3.36 3.92 5.52 6.63 8.06 9.48 10.25 12.39 14.52 17.28 18.83 200 0.91 1.39 1.73 2.32 2.88 3.26 3.46 3.73 4.32 6.25 7.52 9.26 10.94 11.79 14.00 16.30 19.40 20.97 500 1.03 1.57 1.95 2.62 3.25 3.70 3.97 4.21 4.84 7.31 8.78 11.02 13.09 14.04 16.29 18.78 22.34 23.93 1000 1.13 1.72 2.13 2.87 3.55 4.04 4.37 4.59 5.24 8.18 9.80 12.48 14.91 15.93 18.14 20.75 24.71 26.28 4930 0.28 0.47 0.67 1.22 2.05 2.36 2.52 ≈AEP < 2 2 3 7 25 30 34 Storm Report, July 31, 2007; Page 6 RUNOFF Stagecoach Wash Runoff Event of July 31, 2007 A large quantity of precipitation fell quickly on the afternoon of July 31, 2007 near Pima Road and Stagecoach Pass causing a large runoff event at the Stagecoach Wash streamgage (4913). The rain gage at the site (4910) recorded nearly 2.7 inches of rain in about 2 hours with the majority (2.5 inches) falling in about 1 hour. The drainage area of the wash (above the gage) is just over one square mile. Unfortunately, the transducer gage at the site did not properly record the event. It recorded a much smaller peak. Following the event, a large amount of debris was lodged in a bush that was near the pressure transducer housing. The bush appears to have been pushed over toward the transducer. Photographs from May 2007 show the bush much smaller and not near the transducer. Following the event, the transducer was serviced, but no problem was found with its operation. Thus, the reason for the failure is not known. Though the bush seemingly did not cause the failure of the transducer, it was trimmed severely. High water marks at Pima Road were flagged on August 1, 2007. High water marks and debris at the site indicated that the flow covered Pima Road by just over one foot. A survey of high water marks and the channel itself was done on August 22, 2007. Data from three cross sections were collected in a 970 foot reach upstream from Pima Road, and were used to determine the peak discharge for the event. Peak discharge was computed by two methods. First the data were used in a USGSSAC (Slope Area Computation) model. The peak discharge was computed to be 802 cfs. Second, a simple Manning computation was done based on slope and area of the uppermost cross section. The peak discharge was computed to be 808 cfs. Similar results were expected since both computations are based on the Manning equation. However, the SAC program took all three cross sections into consideration. No other inputs into the wash were noted through this reach to the bridge. Furthermore, because of the significant precipitation at the gage site, the granitic soil was likely saturated when the flow occurred, thus minimizing any losses to the wash itself. The peak stage for the event was between 5.1 – 5.2 feet gage height, based on surveyed high water marks at Pima Road. The current rating (#1) shows discharges of 690 – 725 cfs for that range of stages. The peak discharge for the event will be 805 cfs at a stage of 5.10 feet gage height. The rating will be updated to reflect this new information. David E. Gardner, Hydrologist 8/23/2007 Storm Report, July 31, 2007; Page 7 Selected Hydrographs 4863 - Rawhide Wash, 1/3 mile west of Pima Road on Dynamite Blvd. 450 Figure IV 400 350 Discharge (cfs) 300 250 200 150 100 50 0 7/31/2007 18:00 7/31/2007 18:30 7/31/2007 19:00 7/31/2007 19:30 7/31/2007 20:00 7/31/2007 20:30 7/31/2007 21:00 Date / Time 4923 - Cave Creek at Spur Cross 3500 Figure V 3000 Discharge (cfs) 2500 2000 1500 1000 500 0 7/31/2007 18:00 7/31/2007 19:00 7/31/2007 20:00 7/31/2007 21:00 7/31/2007 22:00 7/31/2007 23:00 8/1/2007 0:00 8/1/2007 1:00 8/1/2007 2:00 Date / Time Storm Report, July 31, 2007; Page 8 4889 - Cave Creek 3500 Figure VI 3000 Discharge (cfs) 2500 2000 1500 1000 500 0 7/31/2007 18:00 7/31/2007 19:00 7/31/2007 20:00 7/31/2007 21:00 7/31/2007 22:00 7/31/2007 23:00 8/1/2007 0:00 8/1/2007 1:00 8/1/2007 2:00 Date / Time 4918 - Cave Cr. near Cave Cr. 3500 Figure VII 3000 Discharge (cfs) 2500 2000 1500 1000 500 0 7/31/2007 19:00 7/31/2007 20:00 7/31/2007 21:00 7/31/2007 22:00 7/31/2007 23:00 8/1/2007 0:00 8/1/2007 1:00 8/1/2007 2:00 8/1/2007 3:00 Date / Time Storm Report, July 31, 2007; Page 9 4899 - Cave Buttes Dam 24 Figure VIII 21 18 Gage Height (ft) 15 12 9 6 3 0 7/31/2007 18:00 8/1/2007 6:00 8/1/2007 18:00 8/2/2007 6:00 8/2/2007 18:00 8/3/2007 6:00 8/3/2007 18:00 Date / Time 09511300 - Verde River near Scottsdale, AZ 6000 Figure IX 5500 5000 4500 Discharge (cfs) 4000 3500 3000 2500 2000 1500 1000 500 0 7/31/2007 19:00 7/31/2007 21:00 7/31/2007 23:00 8/1/2007 1:00 8/1/2007 3:00 8/1/2007 5:00 8/1/2007 7:00 8/1/2007 9:00 8/1/2007 11:00 8/1/2007 13:00 8/1/2007 15:00 Date/Time Storm Report, July 31, 2007; Page 10 THOUGHTS The highest measured annual exceedance probability was 93 years for the 1 hour period at Stagecoach Wash. However, Figure III and the graphic below show a number of areas with storm-totals of three inches or more. These values are approximately 20% higher than the 2.68 inches measured at Stagecoach Wash. If we multiply the 1-hour value from Stagecoach of 2.44 inches by 1.2 we get 2.93 inches, which equates to a return period of approximately 350 years. So it is quite likely that significant areas of the Willow Springs, Rowe, Grapevine and Cottonwood Creek watersheds experienced a 100-year or greater storm. Galloway, Andora Hills and Stagecoach Wash watersheds received in general less than 100-year rainfall depths. The high peak flow in Cave Creek was likely do to the contribution from Cottonwood Creek, with a volume contribution from Grapevine/Galloway Washes measured at the Cave Creek gage (4890). Figure X Storm Report, July 31, 2007; Page 11