Potential for travertine formation: Fossil Creek, Arizona

Chemical analyses of water emanating from Fossil Springs in Central Arizona were conducted to predict changes in travertine deposition related to changes in stream discharge caused by diversion for hydroelectric power generation. During spring of 1996, water was sampled at 15 locations during normal seepage flow in a 6.7 km reach below Fossil Springs and at full baseflow during turbine maintenance. Analyses resulted in a rate of 11,923 kg d^-1 of CaCO₃ precipitated from 1218 l s^-1 of water emanating from the springs, while flows of 5.6 l s^-1 that seep past a diversion dam produced 46 kg d^-1 of CaCO₃ precipitation. Active travertine dams currently occur predominantly below the Irving hydroelectric powerplant with partial return of diverted flow back into the natural channel. The lower reach resulted in 519 kg d^-1 of CaCO₃ precipitated from the return of 56.6 l s^-1 with a reduced rate of precipitation during surface runoff conditions due to a dilution effect. Artificial substrates were located at sites in the lower reach for comparison with mass transfer rates derived from changes in water chemistry. Comparison between actual precipitation rates and overall mass transfer rates suggested preferential deposition was occurring at dam locations. Rates of mass transfer for high flow were greater than lower flow. Overall, mass transfer rates for the upper reach were proportional to the flow velocities with total mass transfers for both flows being approximately equal.