A Stochastic Analysis of Flows on Rillitto Creek

Abstract

In order to construct a simulation model for ephemeral streamflow and to examine in depth the problem of the worth of data for that model, measurements of the ephemeral streamflow of Rillitto creek, Tucson, were analyzed for the period 1933-1965. The simulation model was based on several hypotheses: (1) flow durations and their succeeding dry periods (time when no flow is present) are independent; (2) the distribution of the lengths of the dry periods and flows is stationary over a certain period of the year (summer); (3) stationary probability distributions for flow durations and for dry period lengths can be derived. A related problem was how to derive a simulation model for the total amount of flow (in acre-ft) within 1 flow period. Three variables were considered: flow duration (minutes), peak intensity of flow (cu ft/sec) and antecedent dry period-minutes (ADP). Because the assumption of variance constancy does not hold, a multiplicative regression model was used. Using an analysis of variance, which is described in detail, the worth of the 3 kinds of data were examined in relation to total flow. It was concluded that there are at least 5 times during the year when the flow intervals differ significantly, and the ADP is not important in determining flow volume because of the poison flow arrival rate in summer. Events occur at random and are not clustered as in summer, indicating that channel moisture does not differ much between flow events.