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Clesign problems the basic processes are complex and may be difficult to model with the I e f accuracy needed to meet all of the design objectives. River flow through hydr ic stru ures frequently falls into this category. A design process based on the use of doc ented past successes, model verification and "'ftJj~~~ physical modeling, is a und ap'proach. . The DSP RICO poses an especially challenging design because of the requirement that the RICO flow be held to a minimum. This constraint sets a high standard forihe design which wil undoubtedly require a careful, comprehensive approach. ~ Report 2. Note: Several figures in this report are either not properly labeled or are not read~ making it difficult or impossible to accurately evaluate the author's comments. ~, ~ J 0'~/ S~~\j 1. (pp. 24-26) It is not clear how the pool below a U-structure is formed. Since the upstream part of the structure is constructed level with the existing chann:!> it is assumed that the downstream Sid~~:a~~~.d tp ~reate the required drop. 2. (p. 28) The spedfic widths an t1epths used in the weir equation are alluded to but never defined. Th1S'weir equation i he standarclform for flow over a sharp crested rectangular weir. Many modifications to this equation and itsX parameters have been proposed over the years to accommodate different weir geometries and conditions. No evidence has been provided that explains how the weir equation and/or the weir coefficient have been modified to account for the differences between the shape of the U-structure and the standard sharp crested weir. Furthermore, no discussion is given to explain how this equation can be used in the design to "give a general indication of the shapes of the structures". 3. (p. 29-31) An adequate description of the controlling equations, parameters, geometry and other input data is not given in the U-Structure Design Guidance Sheets shown in figures 12 and 13. The tenot tbissectioncontradlcts.the resuJts shown in the tables. For: example, the text referring to figure 12 states, "that at a low flow width of 35 feet the depth in the low flow will be 2.2 feet at 300 cfs". In figure 12.what is actually reported for the low flow is a width of 35 (no units given), depth of 2.231443 (flc) units given) and a flo)^J of 350 cfs. These two statements contradict each other. Other similar contradictior?occur in these tables. In addition there is a discussion of aspect ratio yet this term is not defined within the context of the report. 4. (p. 32, 33) The report repeatedly states that the structures, as represented in figures 14 and ....:', ~j capture, control and divert the flows. The cross section diagrams are offered as proof of tlTfs fact. From an engineering standpoint the cross section graphs do not provide adequate evidence. They~w the apparent intended shape of the cross section. No other evidence is presented to support these claims. 5. (pp. 34, 35) There is no documentation supporting the determination of the minimum flow regimes listed in tables 1 and 2. 6. Tables 1 and 2 present the author minimum flow hydrographs needed to meet the design goals. The subsequent discussion t~ C:lUUUn e qua Itatlve nature of the intended experience at each level. The three discussion points sliow1'l on page 37 are offered as variables considered in arriving at the minimum flow hydrographs. These three bullet points make claims that indicate that the flows were selected based on quantitative analysis. For example,dJrthe second bullet@states that the flows were selected, in part, .... based on the streambed's ability to confine the river into a concentrated channel without creating a flood risk. No evidence is provided to support these claims. Furtherm~ the process used to select the