RESERVOIR SEDIMENTATION ASSESSMENT GUIDELINE - Aneel

Reservoir Sedimentation Assessment Guidelinespecific surveys, with more frequent operations, as is the case for implementing gagingstations for reservoir sedimentation assessment. That network shall remain operationalduring the operation stage.For implementing surveys about river or reservoirs reaches it is useful to know –or measure/monitor – the inflowing of sediments for at least 80% of the inflow basin,being necessary to obtain both suspended and total sediment discharge. For studies onexisting reservoirs, considering an investigation monitoring, it is necessary to monitor atleast 60% of the tributary basin and install a gaging station downstream for identifyingthe effluent sediment. The tributaries that directly discharge into the lake, and report acontribution of sediment higher than 10% of the total tributary shall also be monitored(Yuqian, 1989).7.3 Gaging station installation and measurement frequency***Level readings and net discharge gaging shall be performed when measuringthe sediment discharge, and the gaging station shall be regularly operated. Therefore,the sedimentometric gaging station may be selected among the fluviometric networkgaging stations holding historical data. For installing a new gaging station, the site shallbe selected following the same criteria as for the fluviometric gaging station.In sedimentometric gaging station where it is intended to measure the bed load,it would be useful to use a complementary gaging station, with the same reference andduly located, in order to determine the water line slope for each measurement.The measurement frequency for either the sedimentometric gaging station ornetwork must be planned jointly with the fluviometric network operations; specialattention shall be addressed to the phenomenon of variation for bed sediments duringrainy times and occurrence of precipitations.Usually, the suspended load is the prevailing piece for the total bed sediment;that is why the frequency is establishing aiming at measuring the suspended discharge.The measurement may occur hourly, daily, weekly, monthly or even periodically.Recording devices may perform the continuous operation at a stream point.Hourly measurements may be performed with automatic pumping equipmentwith rotating trays. Daily measures or collection are generally performed by the gagingstation observer in two or three pre-established vertical sections; during drought times,measures are to be performed at every 15 days. In large streams, the sediment collectionmay be performed weekly; however, recent studies on rivers of that nature haveevidenced that such variations may occur even daily.Hydrometry team shall assist monthly or periodic measurements. Suchmeasurements shall be performed following the full sampling criterion and not just forone to three selected vertical sections. Punctual measurement, either using automaticANEEL – Brazilian Electricity Regulatory Agency / SIH – Hydrologic Studies and Information Department16