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70,000 6 Cl .. Z 0 . () . I- W 60,000 (J) 5 ill a: ~ Point of zero flow u. w . ~ a.. I- 50,000 . ~ W J: W 4 ~ u. . () w 10 J: ::::> 40,000 . w () ... (!) < ~ 3 (!) ui . 3: (!) 30,000 0 a: . ...J < u. J: 0 () 2 a: ~ w Cl 20,000 N :.::: u.. < 0 w ~ a.. z ...J 10,000 <5 < ::::> a.. Z Z < 0 0 1970 1975 1980 1985 1990 1995 1997 YEAR Figure 6. POint-of-zero-flow gage height and annual peak discharge, Agua Fria River near Rock Springs, Arizona, 1970-97. charges greater than the lO-year recurrence inter- val. The PZF was 2.93 ft in 1993 and 2.86 ft in 1996. This small decrease appears inconsistent with the large amount of scour measured at the cablewaycross section (fig. 3); however, the chan- nel filled following the high flows of January and February 1993, and the PZF was measured at the control of the gaging station upstream from the cableway primarily during low-flow conditions and may not reflect channel conditions at the cableway. Repeatphotography.--Twos&sofrepem photographs were taken. The first (7 A-B) is of a downstream view taken from the bedrock cliff at the left end of the cableway cross section shown in figure 3. After the large flood on December 18, 1978, the channel is wide, flat, and sandy (fig. 7A). From the cross"'section surveys ofthe reach, the channel had aggraded as a result of the flood. Figure 7B shows tbechannel on June 18, 1998, from about the same perspective. Note that figure 7 B shows tIre reach several years after the large floods that occurred in 1993. The riparian vegetation to the right of the truck in figure 7 B borders a narrow, well-defmed low-flow channel. A view of the right bank of cross-section 3 is shown in figures 8A-B. Figure 8A shows a wide, flat, sandy channel in January 1979. Figure SB shows about the same location and perspective on June 18, 1998. The growth of riparian trees along the low-flow channel obscures the view of the channel itself. The photograph, however, was taken from about the same elevation as that of figure SA. The area with riparian tree growth indicates where several feet of channel incision has occurred since 1978. 09514100 GHa River at Estrella Parkway , near 'Goodyear, Arizona The gaging station, Gila River at Estrella Parkway, near Goodyear, was put into operation in 1991 (fig. 1). Only limited historical cross-section data, therefore, were available for this study, and only one rating curve has been computed for this 12 Determlnatlonof 'CbannelCbange for Selected Streams, Maricopa County, Arizona