approach described in the previous section and the omission of other important factors, most important being the statistical variation of stream discharge. Insufficient data were provided in the in-stream resource assessment group’s final report to reproduce the calculations of recovery factor for the stated example conditions. As noted earlier, Hagerman and Polagye (2006) assert that the distribution of velocities must be used for the power density estimation rather than the mean values, because the cube of the mean current velocity is not the same as the mean of the cubed current velocity. The committee encourages future efforts in in-stream resource assessment to estimate the distribution of technically recoverable resource across the range of flows at all locations. This is particularly important as rivers and streams exhibit large annual and interannual variation in flow. Future work could focus on developing an estimate of channel shape for each stream segment and then, using the flow statistics for each segment along with an assumed array deployment, directly calculating the technically recoverable resource based on equation 3 (above) over the range of expected flows.

Validation

Given the lack of existing deployments of in-stream hydrokinetic arrays as well as the proprietary nature of this industry, little or no field or laboratory data exist to validate the assessment group’s methodology. However, a number of checks could be completed with respect to the reasonableness of the approaches. For example, although considerable effort was expended to develop a methodology to estimate back effects using a modified Manning’s resistance coefficient to account for the resistance that a turbine array will impart on flowing water, limited information is reported with respect to evaluation of the practicality and reasonableness of applying this methodology at various stream conditions. A two- or three-dimensional computational model would be more appropriate to assess the flow resistance effects of the turbine on the flow. The validation effort would also have been stronger if it had focused on questions regarding RF, such as the group’s assertion that slope contributes little to RF. A more thorough assessment of both modified Manning’s coefficient and RF will be necessary to ascertain the validity of these approaches.

Estimate of In-Stream Power Potential

Overall, the in-stream resource assessment group estimates the theoretical resource to be 1,433 TWh/yr and the technically recoverable in-stream resource to be 101.2 TWh/yr. The technical resource is largest



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