Iowa Power Fund Board Project Report Update, July 29, 2009

Climate refers to the long-term course or condition of weather, usually over a time scale of decades and longer. It has been documented that our global climate is changing (IPCC 2007, Copenhagen Diagnosis 2009), and Iowa is no exception. In Iowa, statistically significant changes in our precipitation, streamflow, nighttime minimum temperatures, winter average temperatures, and dewpoint humidity readings have occurred during the past few decades. Iowans are already living with warmer winters, longer growing seasons, warmer nights, higher dew-point temperatures, increased humidity, greater annual streamflows, and more frequent severe precipitation events (Fig. 1-1) than were prevalent during the past 50 years. Some of the impacts of these changes could be construed as positive, and some are negative, particularly the tendency for greater precipitation events and flooding. In the near-term, we may expect these trends to continue as long as climate change is prolonged and exacerbated by increasing greenhouse gas emissions globally from the use of fossil fuels and fertilizers, the clearing of land, and agricultural and industrial emissions. This report documents the impacts of changing climate on Iowa during the past 50 years. It seeks to answer the question, “What are the impacts of climate change in Iowa that have been observed already?” And, “What are the effects on public health, our flora and fauna, agriculture, and the general economy of Iowa?”

Scale Effects in Hydraulic Model Tests of Rock Protected Structures, HR-119, 1970

A laboratory investigation was undertaken to determine the limiting model Reynolds number above which the scour behavior of rock protected structures can be reproduced in hydraulic models scaled according to the Froude criterion. A submerged jet was passed over an initially full scour pocket containing uniform glass spheres and the rate of scour was measured as a function of time. The dimensions of the scour pocket and jet and the particle diameters were varied as needed to maintain strict geometric similarity. For each of two different Froude numbers the Reynolds number was varied over a wide range. The normalized scour rate was found to be practically independent of the Reynolds number, R, (based on the jet velocity and particle diameter) at values of R above about 2.5 x 10^3, and to decrease with Rat smaller values. A grid placed in the jet was found to have a very strong effect on the scour rate. In an attempt to explain the effect of R on the scour behavior, turbulent pressure and velocity fluctuations were measured in air flows and water flows, respectively, over rigid scour pockets having the same geometry as those formed in the scour experiments. The normalized spectra of the fluctuations were found to be nearly independent of R, but the flow pattern was found to be very sensitive to the inlet condition, the jet deflecting upward or downward in a not wholly explainable manner. This indicates that scour behavior can be modeled only if the approach flow is also accurately modeled.