The discharge and volume of flow in a peak decrease as the peak moves through an 89-mile (143 km) reach of the Santa Cruz River. An average of three peaks per year flow the length of the reach. Of 17,500 acre-ft (21,600 dam**3) that entered the upstream end of the reach, 2300 acre-ft (2,840 dam**3), 13 percent of the inflow, left the reach as streamflow. The remainder was lost through infiltration. Losses in a reach of channel were estimated by relating losses to the discharge at the upstream end of the reach. Tributary inflow was estimated through the use of synthesized duration curves. Streamflow losses along mountain fronts were estimated through the use of an electric analog model and by relating losses shown by the model to the median altitude of the contributing area.