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

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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

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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".

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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. No stream flow data have been recorded above Fossil Springs dam. Therefore, FERC used the annual flow duration curves for neighboring watersheds (Wet Beaver Creek, West Clear Creek, Wet Bottom Creek, Red Tank Draw, and Dry Beaver Creek) to derive an estimated flow duration curve for Fossil Creek. FERC estimates that Fossil Springs generates about 77 percent of the total volume of water yielded by the Fossil Creek watershed above the Irving Power Plant. Flows exceed the 43 cfs spring base flow about 23 percent of the time, at commonly encountered flow rates of several hundred to several thousand cfs mainly during snow melt runoff and periodic thunderstorms. Periodic floods augment flows in Fossil Creek throughout the year. Climate in the vicinity of the project is characterized by hot summers, mild winters, moderate precipitation and abundant sunshine. Precipitation records have been maintained at Childs since 1915 and at Irving since 1951 (APS 1991). Average annual precipitation at these sites is 18.1 and 19.9 inches, respectively. Almost half of this precipitation is received between November and March as rain or occasional snowfall. Much of the remainder falls in July and August during thunderstorms. Even though about one-third of the precipitation received in this area is during the summer, the percentage of runoff is negligible. August is the wettest month of the year, yet less than two percent of the total annual runoff occurs during this month. The reduced runoff can be attributed to the high air temperatures and associated high rates of evapotranspiration that are common to this area of central Arizona (FERC 1997 @ DEA pp. 18-19). Water Withdrawals For Hydropower Generation The power plants withdraw 43 cfs from the Irving reach of Fossil Creek (Fossil Springs darn to Irving plant) and 41 cfs in the Childs reach of Fossil Creek (Irving Plant to the confluence with the Verde River). The 2 cfs reduction in conveyance from the Irving plant is due to travertine deposition and resulting constriction in the water conveyance system between the Irving plant and Stehr Lake. That 2 cfs is returned to the Creek at the Irving plant diversion. Despite the withdrawals, reports from the staff at the APS Childs Sr Irving plant indicate that continuous stream flows of various quantities occur throughout Fossil Creek all year round. This flow is derived from precipitation on the Fossil Creek watershed, the 2 cfs return flow at Irving, and a small amount of under flow (0.2 cfs) at the Fossil Springs dam. 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). Periodic Flooding It cannot be overemphasized that Fossil Creek is a "flashy" mountain stream which is subject to frequent and sometimes massive flows of water. Direct evidence of at least four floods exceeding the 30 year recurrence interval within the past 100 years is preserved within the geologic record on Fossil Creek. These are massive destructive events that tend to reshape the stream channel. The evidence of these floods includes vegetative flood debris, erosion scars, and slack water silt deposits.

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Floods on Fossil Creek are characterized by extremely high flow velocities. Floods in excess of a 5 year recurrence interval may have peak velocities of 8 to 10 fps. These velocities are capable of transporting cobbles and small boulders, in addition to significant quantities of finer sediments. Overbank deposits of cobbles and boulders testify to the high transport capacity and flood velocity. One hundred year recurrence interval velocities exceed 15 fps. At least one flood exceeding the 100 year flow rate is preserved in the geologic record. The most recent 100 year flood event occurred in January and February 1993. Although no clear relation between rainfall depth and flood peaks has been developed, the March 1991 rainstorm of 5.35 to 5.87 inches over 3 days produced a flood that peaked at approximately 7,000 cis. The average rate of rainfall for this storm (2 inches/day) was exceeded numerous times in the 76 year historic record ending in 1991. The total rainfall depth for the 1991 storm was exceeded at least 3 times during the period of record (APS 1992 @ Vol. III pg. 21-22). Floods that overflow the low flow channel banks and transport significant quantities of sediment and debris occur about every other year. These flows would also be expected to alter travertine deposition. Peak flows were calculated by Loomis under various watershed conditions for the purpose of evaluating the peak flow of various flood events under conditions resulting from livestock grazing on the Fossil Creek watershed. These values are listed in Table 1. Table 1. Fossil Creek Peak Flows And Recurrence Intervals Under Various Watershed Conditions Source: Loomis, 1994. Recurrence Interval Overgrazed Current Natural (yrs) (cfs) (cfs) (cfs) 2 1124 1026 9-25 -- 5 2403 2257 2089 10 3951 3737 3499 25 6360 6034 5668 50 9438 8998 8510 100 14099 13531 12867

Loomis evaluated the erosion potential under each condition by calculating the amount of shear stress or tractive force exerted by flood flows on the bed material of each of four cross sections in the Irving reach. The estimates of tractive force was used to calculate the largest sediment particle that could be set in motion by various flows.

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Table 2 provides a summary of Loomis's findings on the average maximum sediment diameter set in motion.

Table 2. Average Maximum Sediment Diameter Set In Motion Source: Loomis 1994

Watershed 10 Year Flood 50 Year Flood 100Year Hood Condition (inches) (inches) (inches) Overgrazed 11.0 14.9 16.4 Current 10.8 14.6 16.1 Natural 10.5 14.3 15.8

Each of the three conditions evaluated has a significant erosion potential. Also, there is little change in erosion potential from flood flows between the different sets of watershed conditions. That is each condition has a high destructive potential. Historical accounts of travertine pools and dams in the Irving reach of Fossil Creek and relic travertine structures evident today support the conclusion that travertine will develop with increased flow. It is also clear from the paleohydrologic record that flood erosion will greatly effect deposition and resultant geomorphology. The rate of travertine development and spatial distribution is likely to vary greatly due to a variety of factors including water chemistry, water temperature, shade, turbulence, dilution from runoff, destructive floods, and other factors. The historical record suggests that no significant travertine development in the Childs reach is likely to occur ostensibly because available calcium carbonate tends to be deposited primarily in the upper reaches of Fossil Creek. Water Chemistry Water chemistry data is available from studies conducted by the Arizona Department Of Environmental Quality (ADEQ) and APS. Fossil Creek (reach number 15060203-024) has been monitored by ADEQ and was reported in the ArizonaWater Quality Assessment 1996, as "full support' for Aquatic Sr Wildlife Use-warm water fishery, Full Body Contact (swimming) Use, Agricultural Irrigation Use, and Agricultural Livestock Watering Use. No significant findings were reported relative to the presence of other contaminants. APS completed water quality sampling in locations on the Verde River and Fossil Creek on November 9, 1989 and May 24, 1990. A summary of the Field Parameter Measurements is contained in Tables 3 and Table 4 below.

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Table 3. Field Parameter Measurements November 9, 1989 (Dames & Moore 1990) Sample Location/Number Conductivity Dissolved Oxygen (1) Temperature pH (umohs/cm) (% sat/ppm) (Degrees F) Verde River (2)/VRU-1 70 90/9.9 51 7.0 Verde River (2)/VRU-2 76 93/10.3 51 6.0-7.0 Verde River (2)/VRU-3 76 93/10.3 51 6.0-7.0 Verde River (2)/VRU-4 76 93/10.3 51 6.0-7.0 Verde River (3)/VRD-1 64 96/9.6 60 7.0 Verde River (3/VRD-2 64 94/9.8 53.5 7.0 Verde River (3)/VRD-3 65 94/10.2 52 6.0-7.0 Verde River (3)/VRD-4 74 94/10.4 51 7.0 Childs Effluent/CH-1,CH-2 62 80/7.3 65 7.0 Stehr Lake 68 82/7.2 64 7.0 Effluent/STR-3,STR-4

Stehr Lake 70 80/7.1 67 6.5 Influent/STR-3,STR-4

Fossil Creek/FC-1,FC-2 70 75/6.6 67 7.0

Footnotes: (1) dissolved oxygen figures are not corrected for barometric pressure (2) 300' upstream of the confluence of the Fossil Creek Outfall from the Childs plant (3) 250' downstream of the confluence of the Fossil Creek Outfall from the Childs plant CH-1, filtered, Childs outfall CH-2, unfiltered, Childs outfall STR-1, unfiltered, Stehr Lake flume inlet STR-2, filtered, Stehr Lake flume inlet STR-3, unfiltered, Stehr Lake USGS gauging station FC-1, unfiltered, Fossil Creek Springs flume inlet FC-2, filtered, Fossil Creek Springs flume inlet

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Table 4. Field Parameter Measurements May 24, 1990 (Dames & Moore 1990)

Sample Location Dissolved Oxygen pH EC Temperature (ppm) (Degrees F) Fossil Creek (1) 7.9 7.53 810 69 Stehr Lake Inf all (2) 8.3 7.73 790 69 Stehr Lake Outfall (3) 8.4 7.84 720 69 Childs Plant (4) 9.5 819 700 68.5

Footnotes: (1) Fossil Creek Springs-just above the inlet to the flume to the Irving Generating station (2) Flume outlet to Stehr Lake - approximately 20 feet below the concrete footing of the USGS gauging station (3) Flume inlet from Stehr Lake to the Childs generating station - just above the flume (4) Childs plant outfall - pool just below the generating station

Water samples collected on November 1989 were analyzed for a wide variety of additional parameters. Parameters that exceeded their respective detection limit and the range of concentrations are listed in Table 5 and Table 6 below.

Table 5. Parameters Exceeded and Range Of Concentrations Detected 11/89 (Filtered Samples) (Dames and Moore 1990) Parameter Range Of Concentrations Detected Barium 0.150 mg/I to 0.152 mg/1 Zinc 0.014 mg/1 to 0.018 mg/1 (STR-4) Sulfides 1.20 mg/1 to 4.40 mg/1 Nitrate 0.10 mg/I to 0.14 mg/1 Kjeldahl 0.20 mg/1 (STR-4) Coliform >16 colonies Turbidity 0.23 ntu to 0.59 ntu

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Table 6. Parameters Exceeded and Range Of Concentrations Detected (Unfiltered Samples) (Dames and Moore 1990)

Parameter Range Of Concentrations Detected Barium 0.150 mg/I to 0.157 mg/1 Sulfides <1.0 mg/1 to 1.8 mg/1 Nitrate 0.09 mg/1 to 0.13 mg/1 Kjeldahl 0.20 mg/I (STR-1) Coliform >16 colonies Turbidity 0.23 ntu to 0.56 ntu

In addition to the data noted above, on June 29, 1990, pH values were determined by APS as follows: Fossil Springs flume inlet (7.53), Stehr Lake flume inlet (7.73) and outfall (7.84), and the Childs plant outfall (8.19). Fossil Creek Stream Flow Alternatives Under Consideration By FERC Current Operations Continuation of current operations is the "no action" alternative listed in the DEA. Neither APS or FERC recommends this alternative. However, for FERC licensing purposes, current operations is the environmental baseline against which other alternatives must be evaluated. As noted earlier, no gauging records are available for Fossil Creek. 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). FERC Staff Recommended Alternative FERC has recommended acceptance of the proposal by AI'S to establish new minimum flow release requirements of 10 cfs in the Irving reach and 5 cfs in the Childs reach. This proposal was developed through discussion with an interdisciplinary team comprised of representatives of USFWS, ADG&F and USFS. If approved, these minimum flow releases will begin within one year of license issuance and continue throughout the life of the license (30 years). Minimum flow releases will add to existing flows with expected improvements in aquatic habitat, riparian habitat, and travertine deposition in Fossil Creek, while allowing continued economic operation of the Childs et Irving facilities.

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Return Of Natural Base Flo Other alternatives being considered are a) the return of the full 43 cfs flow to Fossil Creek with decommissioning of the Irving flume and related structures and b) return of 43 cfs flow to the Irving reach and 5 cfs to the Childs reach with complete decommissioning of the Irving flume and related structures. The later decommissioning alternative will not allow economic operation of the project. Therefore, the only true decommissioning alternative is a) return of the full 43 cfs flow. Under this alternative the 43 cfs base flow from Fossil Springs would exist from the springs to the confluence with the Verde River. The plant facilities would be decommissioned at an estimated cost of about $19 million. Travertine Geomorphology Geologic Setting Of Fossil Creek Overby and Neary (1996) have provided an excellent summary of the geologic setting of Fossil Creek as follows: "Fossil Creek is located at the southern edge of the Mormon segment of the Mogollon Rim (Pierce 1987). It is characterized by Miocene aged volcanic material (9.3 to 10.2 million years) overlaying relatively Paleozoic (Mississippian, Pennsylvanian, and Permian) sedimentary rocks of the ancestral rim. To the south of Fossil Creek, the Tonto segment of the Mogollon Rim is relatively free of volcanic material. This whole sequence is best viewed on the north wall of Fossil Creek Canyon. The stratigraphic nomenclature for the Paleozoic sequence seen in Fossil Creek Canyon was recently revised by Blakey (1990). The Kaibab Limestone formation is mostly eroded away, leaving the Coconino Sandstone, Schenbly Hill Formation, the Supai Formation, and the Naco Formation overlaying the Mississippian Redwall Limestone. The Naco Formation consists of Pennsylvanian aged intercalculated limestone, limey mudstone, and some sandstones with numerous unconformities. At Fossil Creek, the formation is near its northern edge, with approximately 10 percent carbonate rocks, and a thickness of about 100 meters. It thickens to 200 meters as it tilts to the Southeast in the Fort Apache area (Blakey 1990). On the Southern edge of the Colorado Plateau, faulting and plateau uplifts are important processes in cutting of canyons. At Fossil Creek, only the latter appears to be important (Pierce 1987). Several uplift episodes, most notably the late Miocene Colorado Plateau uplift, contributed to the cutting of Fossil Creek down to the level of the Naco Formation". F.R Twenter (1961) made the following report on the significance of volcanic rock in the Fossil Creek area:

"The volcanic rocks in the Fossil Creek area are more than 3,000 feet thick. At the junction of Fossil Creek and the Verde river, the lowermost exposed volcanic rocks are at an elevation of 2,500 feet. On the small plateaus that border Fossil Creek near Fossil Springs, the uppermost beds are at an elevation of about 5,800 feet. For the most part, those rocks that form the steep canyon walls are horizontal or nearly so, and are unbroken by major

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faults; therefore the thickness given for the volcanic rocks probably is not exaggerated because of structure. East of Fossil Springs, flat lying Paleozoic rocks, which represent a part of the ancestral Mogollon Rim, are exposed to an elevation of n-tore than 6,000 feet. Here the volcanic rocks are absent, or occur only as a thin cap rock. The change from volcanic rocks west of the Foesil Springs to sedimentary rocks of Paleozoic age east of the springs occurs in a lateral distance of less than 1 mile. The discordant contact between the volcanic rocks and the Paleozoic rocks, which also is well exposed in the West Clear Creek canyon, is attributable primarily to erosional and depositional processes. Prior to accumulation of the volcanic rocks, the ancestral Mogollon Rim in the Fossil Creek area was a prominent escarpment of Paleozoic rocks rising more than 3,000 feet above the floor of the ancient Verde River Valley, and was quite similar in appearance to the present rim near Sedona. Volcanic activity, which began in Miocene time and lasted to early Pliocene time, resulted in the ancient valley being filled with basaltic lavas, tuffaceous sediments, and pyroclastics. The accumulation of volcanic rocks in the Fossil Creek area, which in the final stages may have been contemporaneous with uplift in the Southern part of the Black Hills, impounded the Southward flowing Verde River. Several thousand feet of sediments that now form the Verde Formation were deposited in the newly formed basin and can be seen overlaying the eroded surface of the volcanic rocks in several places in the Verde Valley. A similar relation of the volcanic rocks to the Pliocene lacustrine and fluvial sediments can be seen in Tonto Basin." Travertine Geochemistry Travertine is a cyclically precipitated, calcium carbonate deposit, typically formed in freshwater streams below springs originating in limestone (marine calcium carbonate). It typically has a color banded appearance ranging from hard and crystalline to soft, vuggy (to cavernous), porous, and chalky (tufa), but can also have an approximately spherical/concretionary characteristic (pisolitic). Travertines are precipitated upon or within algae and moss. Calcium carbonate precipitation that forms travertine is a combination of inorganic processes that are accelerated by aquatic organisms. Water coming from the springs is saturated with calcium carbonate, at a relatively low temperature (summer months) and a relatively high carbon dioxide concentration compared to the atmospheric concentration. The partial pressure of CO2 in carbonate saturated groundwater is usually 10 - 100 times greater than atmospheric levels, so CO2 is outgassed by the carbonate waters in order to equilibrate with the atmosphere. Both an increase in temperature and loss of carbon dioxide can cause the precipitation of calcium carbonate. Streams running over falls and steep gradients cause the carbon dioxide to equilibrate more quickly with much lower atmospheric levels, in turn, causing pH to rise and calcium carbonate to precipitate. The aquatic organism' use of carbon dioxide in photosynthesis may also increase pH and cause precipitation of calcium carbonate.

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Outgassing of carbon dioxide in turbulent portions of Fossil Creek has resulted in precipitation of calcite, thereby creating a complex series of travertine terraces prior to the construction of the Childs dr Irving hydroelectric plants, as described below.

Historical Travertine Development and Destniction In The Irving Reach Of Fossil Creek Historical accounts of travertine report large travertine dams in the channel of what is now the Irving reach. In 1891, Charles F. Lummis described waters in Fossil Creek as "so impregnated with mineral that they are constantly building great round basins for themselves, and for a long distance flow down over bowl and bowl". In 1904, F.M. Chamberlain reported dams in the Irving reach "from several inches to a few feet in height, the highest is said to be 10 feet" and pools, the largest of which were "50 to 60 yards long, 20 to 30 feet wide, and approximately 20 feet or more deep".

The travertine that Luumis and Chamberlain saw was destroyed in subsequent floods exacerbated by heavy overgrazing in the Fossil Creek watershed prior to the construction of the Childs & Irving project.

Today there is evidence of historic deposition in Fossil Creek and relict travertine deposits appear above the current stream channel. Overby reported a minimum of 81 distinct sets of travertine dams located mainly near channel nick points where water turbulence increases (Overby et al 1996). He did not report on the criteria used to count structures and his report has not been verified by additional study. There is no data on when these relic structures existed in geologic time. It is important to note that it is not likely that these structures existed contemporaneously. Rather, individual structures probably existed at different periods throughout geologic time.

The diminished amount of travertine in the stream today is due to the diversion of stream flows from the natural channel, periodic flooding, and past livestock grazing. Travertine is currently being deposited on the project flume and other project facilities and in Fossil Creek below the Irving plant where it creates small darns and other structures. Travertine Deposition Estimates: Arizona Public Service Company In 1992, APS obtained pH values from a water quality study (June 29, 1990) and calculated estimated travertine deposition rates in Fossil Creek. They reported the following findings.

The amount of calcium carbonate that would be in equilibrium with the water at the four pH values noted was calculated for each of four locations: Fossil Springs flume inlet (7.53), Stehr Lake flume inlet (7.73) and outfall (7.84), and the Childs plant outfall (8.19). Based on the pH measured, approximately 175 pounds of calcium carbonate per day per cfs would be precipitated between Fossil Springs and the Rehr Lake flume inlet. This is equivalent to approximately 32 tons of calcium carbonate per year per cfs that can precipitate from a pH change from 7.53 to 7.73. Only approximately 40 pounds per day per cfs would be precipitated in Stehr Lake. However, approximately 128 pounds per day per cfs would be precipitated between the Stehr Lake outlet and the Childs plant outfall. APS's estimate of deposition in the Childs reach is not supported in the historic record.

APS cautioned that their calculations are estimates based on a limited set of pH values and therefore apply only under the limited circumstances studied.

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APS's estimated values must be multiplied by the flow rate (cfs), a factor to convert to cubic feet of precipitation (conservatively 0.006 cubic feet per pound), and divided by the surface area over which the water flows to calculate a uniform precipitation amount for the summer months. APS also reported that data do not exist to directly predict Fossil Creek travertine deposition rates. However, the calculated rate of 175 pounds per day of calcium carbonate per cfs in the Fossil Springs/Stehr Lake segment of the project system would likely be exceeded in the Fossil Creek between the Fossil Springs Diversion dam and the Irving plant. This would translate to more than 1,375 tons of travertine deposition per year (7,534 pounds/day) if all 43 cfs were released to Fossil Creek. If evenly distributed over the 4 miles of this reach, it would accumulate at about 0.29 inch per year. More likely, the distribution would be very uneven, both spatially and seasonally. In Fossil Creek, calcium carbonate would be preferentially precipitated in open sunlight areas where there are abrupt changes in either water velocity or slope changes that create falls. These are optimal environments for both inorganic and organic precipitation processes. Travertine precipitation will also occur in heavily shaded areas where the water is strongly agitated and loses carbon dioxide. Precipitation in this latter case is mostly by inorganic processes. Both processes can be significant and neither is more significant than the other. Therefore, pool development would likely occur in both open sunlight and shaded areas. As noted above, storm events and subsequent flooding would likely have a significant effect on the stability of travertine formations. Fossil Creek is subject to regular flooding, which is likely to result in periodic, localized losses of travertine deposits.(APS 1992, Vol. II pg. E2-7 to E2-8) Travertine Deposition Estimates: Federal Energy Regulatory Commission In their 1997 Draft Environmental Assessment, FERC reported the following: "Using the available information, we conclude that travertine deposition could increase under any of the increased flow alternatives, including decommissioning. But because many factors contribute to travertine deposition and deterioration, the amount of deposition and how it would develop in Fossil Creek can't effectively be predicted. Therefore, to determine the amount of travertine deposition from any increase in flows and how it affects other resources (see the discussion in Section V.C.2., Aquatic Resources), monitoring is needed" (FERC 1997 @ DEA pg. 16). "The questions of whether more travertine would form with higher minimum flows and whether travertine would benefit or harm aquatic resources cart only be answered by releasing higher flows and studying the results over a period of years, as Public Service proposes and the commenters recommended." (FERC 1997 @ DEA Section VII. "Comprehensive Development and Recommended Alternative: Travertine and Aquatic Resources Monitoring", pg. 93) "Decommissioning the Irving Development would allow the preproject cycle of travertine formation and destruction to start again in the Irving reach. But the effect of increased flows over time on the size and shape of travertine structures can't be quantified" (FERC

FERC PROJECT NO. 2069-003 ARIZONA *CHIL05 3 IRVING HYDRCPOWER PROJECT' POSER_ CREEK wvortoLoov & TRAVERTINE GUAM:Abut:x..00y PAGE 16

1997 0 DEA Section VII. "Comprehensive Development and Recommended Alternative: Effects Of Decommissioning Irving", pg. 87). "In general, it is unlikely that water surface elevations within the channel and water table elevations in the adjacent alluvium would increase over time as travertine dams form across the stream channel. Travertine formations should break up the existing large habitat units into smaller, more complex habitat units. The Irving reach is likely to become a step/pool system as opposed to the predominantly riffle/run system that exists in the upper portions of the Irving reach today. Travertine deposition should provide more low flow cover and high flow refuge. Width of the water surface would likely increase as water surface elevation increases and stream velocity would likely slow as effective slope is reduced. Game and Fish is concerned that travertine could cause the following adverse effects: (1) travertine terraces could become barriers to fish movement; (2) travertine deposition on the bottom could act as cement, reducing the interstitial spaces in the substrate needed for invertebrate production; and (3) travertine deposition could reduce the amount of clean spawning gravel for fish (letter from James E. Burton, Habitat Branch Chief, Arizona Game and Fish Department, Phoenix, Arizona, May 25, 1994)." (FERC 1997 @ DEA Section V.C.2. "Aquatic Resources, Conclusions", pg. 40) "Intuitively we would expect the natural flow regime to provide the best conditions for the native fish populations of Fossil Creek. Without historic stream morphology associated with travertine formations, however, the wetted perimeter and IFIM analyses show that lower flow alternatives would better enhance the existing habitat. The wetted perimeter analysis predicts that a flow of about 16 cfs, rather than 43 cfs in the Irving reach, would provide more habitat for macroinvertebrate production. In addition, the IFIM study predicts that a flow of 43 cfs in the Irving reach would provide the least WUA of all the flow alternatives for all life stages of all fish species considered in the study except adult and juvenile desert sucker." (FERC 1997 @ DEA Section VII. "Comprehensive Development and Recommended Alternative: Effects Of Decommissioning Irving", pg. 87) "Decommissioning the entire project might allow travertine formation and destruction to start again in the Irving reach. We wouldn't expect travertine to appear in the Childs reach, however, because historical accounts mention the mineral's occurrence only in the first few miles downstream of the springs" (FERC 1997 0 DEA Section VII. "Comprehensive Development And Recommended Alternative: Effects Of Decommissioning The Entire Project", pg. 88-89). "Again we see that restoring natural flows under existing conditions does not provide the greatest [environmental] benefit. The Childs reach is comparable to the Irving reach insofar as the IFIM and wetted perimeter analyses both show that lower flows would provide more enhancement to the fish resource. A flow of 43 cfs in the Childs reach would provide the least WUA of all the flow alternatives for all life stages of all fish species considered in the IFIM study. In addition, the wetted perimeter analysis again predicts that a flow of 16 cfs in the Childs reach would provide more habitat for rnacroinvertebrate production." (FERC 1997 DEA Section VII. "Comprehensive Development And Recommended Alternative: Effects Of Decommissioning The Entire Project", pg. 88-89)

FERC PRozoT No. 2009-003 ARIZONA 'CHILDS & IRVING HYDROPOWER PROJECT' FOSSIL CREEK HYDROLOGY & TRAVERTINE GEOIAORPHOLOGy PAGE 17

aquatic invertebrate production and riffle habitat increase with flow, although the rate of gain begins to diminish above 16 cfs. Travertine deposition and riparian vegetation may increase at higher minimum flows, although as we say in the sections on geological and terrestrial resources, we aren't sure. A particularly noticeable increase in visual character occurs when flows increase from existing conditions to 5 cfs, but visual character continues to increase with higher flows. Recreational use of Fossil Creek would increase with increased flows, especially if travertine basins and falls form. Some resources, however, might suffer adverse effects from higher flows. The IFIM study shows that WUA for the three pool dwelling species evaluated generally decreases as the flows increase above existing conditions. Increased recreational use as a result of increased flows could lead to damage of the riparian zone, so that gains in riparian vegetation permitted by higher flows wouldn't be completely realized. Increased recreational use could also increase vandalism and inadvertent disturbance of the Historic Facilities and eligible archeological sites. Also, the possibility that travertine deposition could adversely affect aquatic resources by cementing the stream bottom" (FERC 1997 DEA Section VII. Comprehensive Development And Recommended Alternative: Effects Of Decommissioning The Entire Project, Issue: Whether to increase the minimum flow releases to enhance fish populations, travertine deposition, riparian vegetation, recreational opportunities, and visual resources, and if so by how much?", pg. 90) Travertine Deposition Estimates: Iohn Malusa, Master of Science Candidate, Department Of Geology, NAU In August 1997, John Malusa submitted a thesis to the Department of Geology at NAU in partial fulfillment of degree requirements for a Master of Science degree in Geology. His study evaluated travertine deposition in Fossil Creek during the spring of 1996 during a period when subject portions of Fossil Creek were flowing under full base flow (43 cfs) conditions. His conclusions were referenced by FERC in the DEA at pg. 15 as follows... "In March 1996, Public Service shut down the Irving powerplant to perform maintenance, and all of the spring's discharge (43 cfs) flowed through the Irving reach for one month. During that month, travertine in the Irving reach accumulated to depths of 1 foot by incorporating woody debris flushed into the channel (Overby and Neary, 1996)." (FERC 1997 0 DEA Section V.C.1.a. "Travertine", pg. 15) Mr. Malusa's thesis concludes that calcite precipitation in the Irving reach is directly proportional to the amount of base flow existing below the Fossil Springs Diversion dam and that with full base flows, precipitation is estimated to be 11,951 kg/day or 26,347 pounds! day. Discussion Of Travertine Deposition Estimates Overall estimates of travertine deposition under increased flow conditions of 43 cfs vary widely from APS's estimate of 7,534 pounds/day in the Irving reach to Malusa's estimate of 26,347 pounds! day in the same reach. Both estimates are based on limited data and modeling approaches that provide only gross estimates. Neither is likely to predict actual deposition quantities. However, these estimates are useful in understanding the possible range of deposition rates that may occur in various portions of the Irving reach.

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Clearly, travertine deposition will increase under any increased flow alternative. It is also clear that erosion forces due to flooding will have major alteration and deformational effects on travertine development. The rate of sustained travertine development in Fossil Creek will depend on a number of complex factors that will result in variable deposition throughout the Irving reach both in terms of quantity and spatial distribution. The questions of whether more travertine would form with higher minimum flows and whether travertine would benefit or harm aquatic resources can only be answered by releasing higher flows and studying the results over a period of years.

W.L. Bouchard Sr Associates, Inc. Phoenix, Arizona June 25, 1998

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References Natural Springs In Arizona Feth, J.H. and Hem, J.D., US. Geological Survey, Menlo Park, California and Denver, Colorado, "Springs Along The Mogollon Rim In Arizona", New Mexico Geological Society Thirteenth Field Conference, circa 1961. Verde River House, Kyle P., Pearthree, Philip A., and Fuller, Johnathon E., Arizona Geological Survey, "Hydrologic and Paleohydrologic Assessment of the 1993 Floods on the Verde River, Central Arizona", Arizona Geological Survey Open File Report 95-20, December 1995. Pearthree, Philip A., Arizona Geological Survey, "Geologic and Geomorphic Setting of the Verde River from Sullivan Lake to Horseshoe Reservoir", Arizona Geological Survey Open File Report 93-4, March 1993. Fossil Springs and Fossil Creek Arizona Public Service Company, Application For New License For Major Prcject - Existing Dam: Childs & Irving Hydroelectric Project, FERC Project No. 2069-003 Arizona, Volumes I-III, December 1992.

Arizona Public Service Company, Application For New License For Major Project - Existing Dam: Childs & Irving Hydroelectric Project, FERC Project No. 2069-003 Arizona, Volume IV, July 1993. Federal Energy Regulatory Commission (FERC), Draft Environmental Assessment For H dro sower License: Childs Irvin Pr *ect FERC Pr ect No. 2069-003 Arizona August 14, 1997. Malusa, John, "Natural Geochemical Evolution Of A Travertine Depositing Spring: Fossil Springs, Arizona", A Thesis In Partial Fulfillment of the Requirements for the Degree of Master of Science in Geology, Northern Arizona University, August 1997. Overby, Steven T. and Neary, Daniel G., USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Flagstaff, AZ, "Travertine Geomorphology Of Fossil Creek", irce.e4ngs of the 1226 g_laeLy_s of t - ch, y_Secfior izo _ la Academy Of Science, April 20, 1996. Twenter, FR., US Geological Survey, Iowa City, Iowa, "The Significance Of The Volcanic Rocks In The Fossil Creek Area, Arizona", Proceedings Of The New Mexico Geological Society Thirteenth Field Conference, circa 1961. Loomis, Grant, USDA, Forest Service, Tonto National Forest, "Fossil Creek Flood Peaks: Current, Natural and Degraded Watershed Conditions", Technical Report, October 14, 1994. Weir, Gordon W., and Beard, L. Sue, U.S. Geological Survey and Ellis, Clarence E., U.S. Bureau Of Mines, "Mineral Resource Potential Of The Fossil Springs Roadless Area, Yavapai, Gila, and Coconino Counties, Arizona", 1982.

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Keith, S.B., Arizona Bureau Of Mines, Tucson, Arizona "Sandstone", Geology and Mineral Resources of Arizona, Bulletin No. 180, Arizona Bureau Of Mines and U.S. Bureau Of Reclamation, pp. 441-448,1969. "Fossil Creek Diversion To Childs Power Plant Near Camp Verde, Arizona; Station Information" Station Number 09507500, (station located at discharge of flume to Stehr Lake), USGS. "Fossil Creek Diversion To Childs Power Plant Near Camp Verde, Arizona; Current Conditions 5/18/98", USGS. "Historical Strearnflow Daily Values Graph for Fossil Creek Diversion To Childs Power Plant Near Camp Verde, Arizona; 1952-1992", USGS. "Historical Streamflow Daily Values Graph for Fossil Creek Diversion To Childs Power Plant Near Camp Verde, Arizona; 1952 (Weekly)", USGS. "Historical Streamflow Daily Values Graph for Fossil Creek Diversion To Childs Power Plant Near Camp Verde, Arizona;1953 (Weekly)", USGS. "Historical Streamflow Daily Values Graph for Fossil Creek Diversion To Childs Power Plant Near Camp Verde, Arizona; 1954-1959", USGS. "Historical Streamflow Daily Values Graph for Fossil Creek Diversion To Childs Power Plant Near Camp Verde, Arizona; 1960-1964", USGS. "Daily Mean Discharge Data 1960 -1964: Fossil Creek Diversion To Childs Power Plant Near Camp Verde Arizona", USGS. Barrett, Paul James, "Spatial Habitat Preference Of Smallmouth Bass (Micropterus Dolomieui), Roundtail Chub (Gila Robusta), and Razorback Sucker (Xyrauchen Texanus), A Dissertation Submitted to the Faculty of the Department Of Renewable Natural Resources In Partial Fulfillment of the Requirements For The Degree of Doctor Of Philosophy With A Major In Wildlife And Fisheries Science, In The Graduate College, The University Of Arizona, 1992. Sayers, Rebecca C., "Potential Impacts of Stream Flow Diversion on Riparian Vegetation: Fossil Creek Arizona", A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Forestry, Northern Arizona University", May 1998. Chamberlain, F.W., "Fossil Creek", Field Notes On File In The Smithsonian Institute Archives, 1904. Lummis, Charles F., "The Greatest Natural Bridge On Earth", Some Strange Corners Of Our Country The Wonderlands Of The Southwest, 1891. Sullivan, Marie E. and Richardson, Mary E., United States Fish Sr Wildlife Service Arizona Ecological Services Office, Functions And v I es Of The Verde River Ri • arian Ecos stem And An assessment Of Adverse Impacts To These Resources, prepared for the United States Environmental Protection Agency, Region 9, March 1993. Arizona Public Service Company, Rainfall Records Childs Station 01614 11915-1990) and Irving Station 04391 (1951-1990), compiled 1991.

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LuWt k_.eocriurtica r-vrce microscopy', et Cosmochimica Acts, Volume 57, pp. 705-714, 1993. Plummer, L.N., Wigley, T.M.L., and Parkhurst, D.L., "The Kinetics Of Calcite Dissolution In CO2 Water Systems At 5-60 degrees C and 0.0 to 1.0 ATM CO2", American journal Of Science Volume 278, pp. 179-216, February 1978.

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FERC PROJECT NO. 2069-003 ARIZONA "CHILDS & IRVING HYDROPOWER PROJECT'