• A Taxonomy of Small Watershed Rainfall-Runoff

      Hawkins, Richard H.; watershed Science Program, School of Renewable Natural Resources, University of Arizona, Tucson, Arizona 85721 (Arizona-Nevada Academy of Science, 1990-04-21)
      A study of over 11,000 event rainfall and associated direct runoff events from 100 small watersheds was done, in a search for distinct patterns of runoff response and/or association with land type. The results show unexpected variety in the geometry and scale of the rainfall -runoff response. Groupings of similar response type and magnitude were made, and the associations with vegetative cover were tested. Five separate response groups were identified as follows: 1) Inactive, characterized by no recorded responses to any rainstorm in an extended period of record; 2) Complacent, characterized by a very small part of the rainfall (ca 0.1 to 3 percent) being converted to direct runoff, often as a linear response; 3) Standard behavior, the expected "textbook" response common to agricultural lands and humid sites, and in which the runoff slope increases with increasing rainfall, and the scale of runoff far exceeds the complacent response; 4) Violent behavior, in which an abstraction threshold of 2 -6 cm clearly precedes a sudden high response; and 5) Abrupt response in which a very high portion of the rainfall is converted to event runoff without appreciable abstraction, as typified by extensively urbanized drainages. The responses and the group identifications were parameterized by a simple broken -line linear rainfall-runoff equation, and a dichotomous key based on coefficient values is proposed. Only mild associations between response type or coefficient values and the four vegetative covers (Forest, Range, Agriculture, and Urban) were found. The variety of hydrologic behavior on forested watersheds encompassed that of the other three land types.
    • Use of Biotoxicity Tests for Estimating Impact of Stormwaters on Aquatic Life

      Amalfi, Frederick A.; Atkinson, Elizabeth M.; McNaughton, Julie D.; Sommerfeld, Milton R.; Aquatic Consulting & Testing, Inc., Tempe, Arizona; Arizona State University, Tempe, Arizona (Arizona-Nevada Academy of Science, 1990-04-21)
      A test protocol was evaluated for estimating the acute toxicity of urban stormwater runoff to aquatic life. Potential deleterious effects of storm flows on the aquatic community of small artificial impoundments were examined by application of short-term bioassays. Definitive, static renewal, acute toxicity tests were performed using the fathead minnow, Pimephales promelas, and the crustacean, Daphnia magna. The feasibility study indicated that short-term bioassays may provide an alternative to individual chemical constituent measurements and comparisons to numerical water quality criteria for protection of aquatic life. Biotoxicity tests may identify synergistic interactions to chemicals which individually meet specific water quality criteria but collectively lead to toxicity.