Hydropower Resource Assessment at Existing Reclamation Facilities

Chapter 2Hydropower Site Data Collectioncollecting seasonal flow data and estimating net head through fieldinvestigations.Dikes and SiphonsSome sites identified in the 1834 Study are dikes. Dikes typically impoundwater and do not have any flow releases. As a result, the dikes included in thisstudy were assumed to have “no hydropower potential” because of zero flows.If a local representative had data indicating the site was not a typical dike anddid have flows, then it was documented and carried forward in the analysis. Thesame approach applied to sites that were siphons.2.2.2 Net Hydraulic HeadIn addition to flow, sites require a positive net head for hydropowerdevelopment. Net head is calculated as the difference between head water andtail water elevation. In general, a minimum of 3 feet of head is required togenerate some hydropower. For some sites without historic records, local staffwas able to provide information about available head at the sites. If sites hadminimal head available (i.e., less than 3 feet), which occurred mostly in canalsand tunnels, they were noted to have “no hydropower potential” due to thelimited head available to move water within the canal or tunnel.For reservoir dams and diversion dams, the recorded variable reservoirelevations at the site were used as the head water elevation and the tail waterelevation was estimated from record drawings. Tail water elevation was aconstant.For most canals and tunnels, net head was a constant reflecting the elevationdrop in the facilities. Some canals had similar elevation data as reservoirswhere head water elevation varied and tail water elevation was constant.2.3 Data for Canals and TunnelsMany of the sites with further data needs are canals and tunnels. For somecanals, maximum flow data design capacity was available, but seasonalvariations in flow and net head data was not available. Seasonal flowdistribution can significantly affect hydropower potential at a site. ManyReclamation canals are used for irrigation purposes and only carry flows duringthe irrigation season. Irrigation demands can also vary monthly, so canals maynot be operating at peak capacity during the entire irrigation season. As a result,using design capacity flow data to calculate hydropower production is not anaccurate representation of hydropower potential; daily flow data is best.Further, hydropower potential cannot be estimated without data on net head. Alarge portion of the canals listed in the 1834 Study did not identify a specificdrop or drops in the canal. Instead they simply listed the head differential alongthe entire stretch of the canal (sometimes over tens of miles). Elevation changes2-14 – March 2011