Fossil Creek Hydrology & Travertine Geomorphology
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Fossil Creek Hydrology & Travertine Geomorphology FERC Project No. 2069-003 Arizona Childs and Irving Hydropower License Prepared For: Arizona Public Service Company Phoenix, Arizona Prepared By: W.L. Bouchard & Associates, Inc. Phoenix, Arizona June 25, 1998 Fossil Creek Hydrology & Travertine Geomorphology Abstract Fossil Creek is a tributary of the Verde River in Gila and Yavapai Counties in Arizona. Stream flow is composed of a 43 cubic foot per second (cfs) base flow from Fossil Springs (a perennial source of spring flow to the creek) and runoff from precipitation which frequently occurs as destructive flash floods. These sources form 77% and 23% of the flow respectively. Fossil Springs water is supersaturated with calcium carbonate and carbon dioxide and thus tends to precipitate travertine in the upper 4 mile reach of this 14 mile stream. Travertine deposition effects stream morphology. Fossil Creek is a "flashy" stream that frequently conveys large volumes of water very quickly. Significant floods that overflow the low flow channel banks and transport significant quantities of sediment and debris Occur about every other year. These frequent flood flows tend to alter travertine deposition. Periodically, Fossil Creek is subject to very large destructive floods that significantly alter stream morphology. Arizona Public Service Company (APS) owns and operates the Childs & Irving Hydroelectric plants on Fossil Creek. The plants withdraw the 43 cfs base flow about 0.2 miles below the springs for hydropower generation. In 1992, APS proposed to the Federal Energy Regulatory Commission (FERC) to increase minimum flow releases to 10 cfs in the Irving reach and 5 cfs in the Childs reach as part of their application for relicensing. Other alternatives are the "no action" alternative which includes continuation of current operations or decommissioning the plants with return of the 43 cfs base flow to Fossil Creek. Both the increased minimum flow release proposal and the return of full flows alternative are expected to result in increased travertine deposition. Despite the withdrawals, reports from the staff at the APS Childs & Irving plant indicate that Fossil Creek flows continually, throughout its length, all year round, supporting a diverse riparian and aquatic community of plants and animals. This flow is derived from precipitation on the Fossil Creek watershed, a 2 cfs diversion from the flume to the Creek at Irving, and under flow (0.2 cfs) at the Fossil Springs dam. Periodic floods augment flows in Fossil Creek throughout the year. Thunderstorms produce increased flows usually of less than 24 hours in duration. Below the Irving plant in the Childs reach, a similar pattern of flow exists (Bouchard 1998). This report provides detailed information and references relating to the hydrology and travertine geomorphology of Fossil Creek for use in the licensing process. Introduction The Childs & Irving Hydroelectric plants are owned and operated by APS on Fossil Creek, a tributary of the Verde River in Gila and Yavapai Counties in Arizona. The plants provide a valuable source of renewable power, and are listed on the National Register Of Historic Places and also as a National Historic Mechanical Engineering Landmark by the American ftNPKEIN,IRM MENA 'AN a IRVING HYDROPOWZR MET' FOSS& CREEK tine(*.my & TRAVERTINE GEomoRpHowoy PACE 4 The Irving penstock consists of 3,278 lineal feet of 30 to 36 inch steel riveted penstock. The tailrace from the Irving plant discharges directly into the forebay for the Childs flume, without returning to the Fossil Creek channel. The forebay contains a control gate and an overflow gate. A second diversion structure (Fossil Creek diversion dam) is located approximately 350 feet upstream of the Irving plant to allow operation of the Childs plant when the Irving plant is offline. This diversion dam is approximately 27 feet long, 5 feet high, and 5 feet thick at the base tapering to a 1 foot crest thickness. A ditch leads from this diversion to the forebay for the Childs flume. The Childs flume consists of five general types of construction: 1. Approximately 10,300 lineal feet of concrete flume on a bench. The approximate flume dimensions are 6 feet wide by 3½ feet high. 2. Approximately 1,550 lineal feet of 42 inch diameter steel pipe 3. Approximately 3,550 lineal feet of gravity tunnel consisting of six separate tunnels. These arched roof tunnels are approximately 3 1/2 feet wide by 6 feet high and are lined with concrete where required. 4. Approximately 6,930 lineal feet of an inverted siphon across Sally Mae Canyon, consisting of steel riveted pressure pipe approximately 47 5/8 inch inside diameter. The siphon is buried throughout its length, except where it crosses Boulder Creek, Sally Mae Creek, and an unnamed wash. At these crossings, the siphon is carried on steel truss bridges. 5. A 120 inch, semicircular steel flume, approximately 860 feet long, between the siphon and a tunnel. This flume is of the same general construction as the Irving flume. This water conduit has a total length of approximately 23,190 feet from the intake at Irving to its discharge into the regulating reservoir (Stehr Lake). The United States Geological Survey (USGS) operates gauging station No. 09507500 at the Childs flume where it discharges to Stehr Lake. Stehr Lake was constructed for two purposes: storage of up to 3 days flow to allow the Childs plant to operate during flume maintenance or downtime, and as a regulating reservoir. Stehr Lake originally had a surface area of 27.5 acres. During the 89 years of its operation, it has collected sediment and currently impounds approximately 100 acre feet of water. This lake was created by the construction of two earth fill darns, one at each end of a natural depression. Dimensions of the darns are as follows: main (lower) dam height 20 feet, crest length 450 feet, crest width 20 feet, base width 140 feet; upper dam height 12 feet, crest length 1,250 feet, crest width 15 feet, base width 80 feet. The water conveyance downstream from Stehr Lake includes 4,888 lineal feet of concrete lined pressure tunnel with a cross section of 3 1/2 feet by 6 feet and 1,393 lineal feet of 48 inch concrete low head pressure pipe. The concrete pipe terminates in a 30 foot diameter concrete surge tank. The Childs penstock begins at this concrete surge tank and consists of approximately 4,800 lineal feet of steel pipe. The penstock diameter varies from 48 inches at FERC PROJECT NO 2.-M9-,.„..-^^3 ARIZONA 'CHILDS & IRVING HYDROPOWER PROJECT' Possit. MEEK RYDROLOGY & TRAVERTINE GEOMORPHOLOGY PAGE 5 the top to 32 inches at the Childs plant. The upper portions of this penstock consists of a steel riveted section and a lower portion forged steel pipe imported from the Krupp Works of Germany. The tailraces from the Childs plant discharge into the Verde River at a point approximately 3 miles north (upstream) from the confluence of Fossil Creek with the Verde River. The Childs & Irving facilities also includes substations, switchyards, transmission lines, machinery, buildings, shops and living quarters for the use of plant personnel (APS 1992). Fossil Springs Hydrology Natural Base Flow Fossil Creek is a tributary of the Verde River immediately south of the West Clear Creek drainage that flows southwest from the Mogollon Rim. Bordering on the Tonto and Coconino national forests, it ranges in elevation from approximately 7,260 feet near the headwaters to 2,550 feet at confluence with the Verde River. At about the 4,199 feet elevation, a series of springs that are supersaturated with calcium carbonate and dissolved carbon dioxide derived from and flowing out of the Naco geologic formation over a distance of 1000 feet. Spring-generated base flow below the springs is fairly constant at 43 cubic feet per second (cfs). The spring flow has a temperature of 71.6 degrees Fahrenheit (F) throughout the year. No tributaries or significant springs add to the base flow below the Fossil Springs diversion. The stream bed lies directly on bedrock, probably preventing infiltration from flow. Therefore, no significant interaction of groundwater and stream flow is likely, except, where Fossil Springs flows into the creek (APS 1992 Vol. II pg. E2-2). The width of the floodplain in Fossil Creek is severely restricted by the steep precipitous cliffs. However, the active floodplain broadens within 0.5 miles of the Fossil Creek / Verde River confluence (Sullivan 1993). The steep channel gradient, 210 feet per meter, yields high water velocities subject to episodic flood events. The General Ecosystem Survey (USFS 1991) indicates that the erosion hazard potential for the Fossil Creek watershed is severe. The streambed of Fossil Creek is predominantly large cobble and boulder with a lesser amount of bedrock. Over bank shading is limited except in areas dominated by riparian forested broadleaf vegetation adjacent to the active channel. Large stands of mature trees are generally lacking. Isolated pools are present (Sullivan 1993). Travertine Deposition Flows from Fossil Springs are supersaturated with carbon dioxide and calcium carbonate and thus are responsible for travertine formation in Fossil Creek. Travertine consists of calcium carbonate deposited from solution in surface waters. Its structure is concretionary, banded, and often porous. Travertine deposits form on rocks, logs, leaves, and other objects in the stream channel, and will typically create dams, terraces, and other structures within the active stream channel. This phenomenon is described in greater detail below in the section titled. "Travertine Geomorphology". FERC PROJECT No 2069-003 ARIZONA 'CHILDS & MANG NYoRoPowER PROJECT' Fossil CREEK NyoRoLOCY 8, TRAVERTINE GEO•AoRpuoLocY PAGE 6 Flows In Excess Of Base Fl w Due To Runoff From Precipitation FERC has estimated the percentage of average flow that originates from Fossil Springs and the percentage that originates from runoff.