Fossil Creek: Restoring a Unique Ecosystem Item Type text; Proceedings Authors Matthews, Elizabeth; Cain, Tom; Loomis, Grant; Stefferud, Jerome; Martin, Rich Publisher Arizona-Nevada Academy of Science Journal Hydrology and Water Resources in Arizona and the Southwest Rights Copyright ©, where appropriate, is held by the author. Download date 28/09/2021 13:46:57 Link to Item http://hdl.handle.net/10150/296468 FOSSIL CREEK: RESTORING A UNIQUE ECOSYSTEM Elizabeth Mathews and Tom Cainl Grant Loomis, Jerome Stefferud, and Rich Martine Relicensing of the Childs /Irving Hydroelectric at Irving Dam, 0.2 miles downstream from the Project (Childs /Irving) provided an opportunity springs, and is transported 10.4 miles by a series for restoration of a unique travertine ecosystem of open flumes, syphons and penstocks to power in central Arizona. Childs /Irving, located on plants at Irving and Childs. The diverted water Fossil Creek in Gila and Yavapai counties, has is eventually discharged to the Verde River at generated electricity since the early part of this Childs, 4 miles above its confluence with Fossil century. The original hydropower license for Creek. A small reservoir (Stehr Lake) located Childs /Irving was issued on January 1, 1945 by between the power plants at Irving and Childs the Federal Power Commission for a 50 -year provides a 3 -day supply of water to Childs period. In 1994, Arizona Public Service Compa- when the diversion system in the upper wat- ny (APS) applied to the Federal Energy Regula- ershed is shut down. tory Commission (FERC) to relicense the project. The power plants at Irving and Childs have a The relicensing and associated environmental combined generating capacity of 4.2 megawatts assessment process provided a rare opportunity and produce 37,000 mwhrs per year, enough to restore a unique, but degraded travertine power to sustain about 4,000 homes. The Irving ecosystem by restoring streamflow to a mostly plant, constructed in 1915, is located next to Fos- dewatered creek. This paper describes many of sil Creek and 4 miles downstream of the diver- the unique features of the ecosystem and some sion dam. It produces one third of the power of the issues that surfaced during the environ- generated by the two plants. The Childs plant, mental assessment process. constructed in 1908 -1909, was one of the first hydroelectric power plants built in the West. It is The Project located on the banks of the Verde River and From its origin in the incised canyons of the generates the remaining two thirds of the power. Mogollon Rim country just north of Strawberry, Total generating capacity of these plants is less Arizona, Fossil Creek flows in a southwesterly than 0.1 percent of the total power production direction for 17 miles before entering the Verde capacity of APS. The Childs /Irving project was River below Childs. It flows on lands entirely designated as a National Historic Mechanical under the jurisdiction of the National Forest Engineering Landmark in 1976 and was entered Service, and forms the boundary between the into the National Register of Historic Places in Coconino and Tonto national forests for much of 1991. its length. Fossil Creek is an intermittent stream Generation of the power produced by the from its headwaters until it reaches Fossil Childs /Irving plants requires diversion of all of Springs, which are located approximately one the natural discharge of Fossil Springs. Save for third of the way down the mainstream of the leakage of 0.2 cfs at the diversion darn and dis- creek. The springs emerge over a 1,000 foot charge of an additional 2 cfs at the Irving plant, reach of the creek, at a constant discharge of 43 the entire baseflow of the creek is contained cubic feet per second (cfs) and a constant tem- within the water delivery system of the power perature of 72 °F. project. Only flood flows and runoff in excess of In the early 1900s the flow from these springs the capacity of the diversion system (48 cfs) are was diverted from the creek and used to gener- allowed to flow down the natural channel. ate hydroelectric power for the mines near Pres- Childs /Irving was issued a license for a peri- cott, Jerome, and Crown King. Water is diverted od of 50 years on January 1, 1945 by the Federal Power Commission. In 1994, APS applied to the I Coconino National Forest 2Tonto National Forest Federal Energy Regulatory Commission (FERC) 78 Fossil Creek for a new permit. Since 1990, the Forest Service, mg from flood flows. Reduction in baseflow to Arizona Game and Fish Department, and U.S. 0.2 cfs below the diversion dam and to 2 cfs Fish and Wildlife Service have worked closely as below the Irving plant restricts seedlings to a an interagency team with APS to prepare the narrower band within the active channel than relicensing application. The team's sole function probably occurred historically when baseflow was to advise the applicant on affected re- was 43 cfs. sources. The application developed by APS does The aquatic community consists of popula - not consider alternatives for operation of the tions of predominantly native fish species. power plants and diversion works or for main- Above Irving Dam, roundtail chub, desert and taining various flow scenarios in the creek. The Sonora suckers, and speckled dace are naturally Coconino and Tonto national forests are now present, and razorback suckers were stocked in conducting a joint environmental analysis with 1988. Below Irving Dam, the first three species FERC that does consider alternative streamflow are still present, but in greatly reduced numbers scenarios. due to reduction in flow. Longfin dace are also The entire relicensing process takes about 5 found in isolated reaches. Non- native species years and is triggered by the Federal Power Act found below the diversion include green sun- that requires water power operators to be peri- fish; smailmouth bass and yellow bullhead occur odically reevaluated so that, if warranted, the only in the lower 3 to 4 miles of the creek and operation may be either discontinued or modi- probably originate from the Verde River. The fied, to reflect changing societal values, opera- razorback sucker is an endangered species, and tional advancements, or other factors. the remaining native fish species have category 2 status (listing as threatened or endangered may The Ecosystem be appropriate, but data substantiating the list- Vegetation on the upland watershed consists of ing are not available). Razorback suckers are not ponderosa pine forest in the headwaters, fol- native to Fossil Creek although they are native lowed by several plant communities including to Arizona. It is not known whether this popula- chaparral brushlands, pinyon juniper wood- tion will become self -sustaining. The roundtail lands and semi -desert grasslands as the creek chub is the species of greatest concern in Fossil descends. Elevations range from 7260 feet near Creek because of its status under the Endan- the headwaters to 2550 feet at the Verde River gered Species Act and with both the Forest Ser- confluence. Average annual precipitation is 18.1 vice and Arizona Game and Fish Department. inches at Childs and 19.9 inches at Irving. The Sonoran and desert suckers are also of The constant discharge of 43 cfs from Fossil concern because of declining populations Springs represents slightly more than 70 percent throughout their range. of the average annual water yield of the basin The large and sustained baseflow, the pres- above the springs. A diverse aquatic and ripar- ence of a nearly intact native fish community, ian community has developed downstream of and a diverse riparian community all contribute the springs as a result of this reliable and sus- to the remarkable resource values of Fossil tained flow. The riparian community is diverse Creek. But the factor that makes Fossil Creek in both species composition and age structure. unique is that the water discharged from the Woody riparian species include Arizona walnut, springs is laden with calcium carbonate that Arizona sycamore, velvet ash, Arizona alder, precipitates to form travertine deposits when Fremont cottonwood, and willow species. The exposed to atmospheric conditions. Travertine riparian community most closely resembles that deposits are rare in Arizona and are considered of the Arizona sycamore - velvet ash type and to be outstanding natural resources where they appears to be typical of flood -dominated ripar- occur (e.g. Havasu Creek, Tonto Natural Bridge, ian systems in the southwestern United States. and the Little Colorado River). Seedlings are by far the most common age class The waters of Fossil Springs emerge from and are concentrated in a narrow band along the limestone, which provides a geologic environ- fringe of the streams' free water surface. Older ment conducive to the formation of travertine. age classes are more prevalent on terraces Travertine is calcium carbonate deposited from further removed from the active channel of the solution in ground and surface waters. Chem- stream. The proximity of seedlings to the stream ically, travertine is identical to the mineral results in high seedling mortality due to scour- calcite. Water discharged from the springs has Mathews, Cain, Loomis, Stefferud, and Martin 79 high concentrations of calcium carbonate and mile below Fossil Springs. Today, relic travertine dissolved carbon dioxide. As this water travels structures can be found at least 1 mile below downstream and is exposed to the atmosphere, Irving. Near Fossil Springs, massive travertine carbon dioxide gas is released. Release of carbon deposits 100 to 200 feet above the current stream dioxide raises the pH of the water, causing the channel are evidence that travertine must have water to become supersaturated with calcium formed in Fossil Creek for many thousands of carbonate.