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<br />Information generated as input and part of the energy dissipa- <br />tor design output will also be useful in subsequent design <br />phases. The channel characteristics--slope, cross section, <br />normal depth and velocity, bed and bank materials along <br />with the flow characteristics at the dissipator exit, velocity <br />and depth--are all essential to the design of channel protection. <br /> <br />These common data input and output requirements, although <br />very important, are only one reason for considering the <br />culvert, debris control, energy dissipator, and channel <br />protection designs as an integrated system. The interrela- <br />tionship of the various parts or individual designs within <br />the system must be considered. For example, energy dissipators <br />can change culvert performance and channel protection require- <br />ments: some debris-control structures represent losses not <br />normally considered in the culvert des~gn procedure; energy <br />dissipator requirements might be substantially reduced, <br />increased, or possibly eliminated by changes in the culvert <br />design; and downstream channel conditions--velocity, depth <br />and channel stability are important considerations in energy <br />dissipator selection and design. <br /> <br />The designer might also consider energy dissipator design <br />as a a minisystem involving numerous energy dissipation <br />schemes with overlapping selection criteria. A combination <br />of dissipator and channel protection might be used to solve <br />specific problems. Figure 1-1, "Conceptual Model--Energy <br />Dissipator Design," indicates the input, output, and the <br />various steps in the energy dissipator selection and design <br />process. As indicated on the flow chart, the process begins <br />by considering the standard design terminal structures normally <br />employed. The initi~l step is to determine the flow condi- <br />tions at the exit of the standard transition outlet and using <br />these conditions estimate the scour which might be expected <br />if the downstream channel were composed of unconsolidated <br />sand. <br /> <br />This estimate represents an extreme condition; but, by comparing <br />it with the subjective judgment of the erodibility of the <br />actual material present in the channel, the designer is <br />provided with a qualitative measure of the magnitude of the <br />local erosion problem. This input, considered along with <br />data on the long-term stability of the downstream channel <br />which is discussed in the chapter on Erosion Hazards, enables <br />the designer to reach a preliminary decision on energy <br />dissipator needs. <br /> <br />The decision may be that no protection is required; that <br />minimal protection and monitoring after each runoff event <br />is needed: or that an energy dissipator or combination <br />energy dissipator and channel protection is necessary. <br /> <br />1-2 <br />