RESERVOIR SEDIMENTATION ASSESSMENT GUIDELINE - Aneel

More documents

Recommendations

Info

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
Reservoir Sedimentation Assessment Guidelineequipment or register such as hourly, daily or weekly collection, shall be followed bymeasurements performed by the hydrometry expert for calibration purposes.The measurement performed by the hydrometry expert shall include bothsuspended sediment load and bed load collection. The measurement of watertemperature measurement and slope measurement are also required.Most of the stream’s bed sediment occurs during rainy period, corresponding toabout 70 to 90% of annual total load. Therefore, it is useful that measurement frequencycomprises such period, and that few measurements remain for drought period.Sediment measurements are relatively more expensive than the remainingmeasurements for water resources surveys, due to the complexity of the phenomenonand to its difficult computation, as well. Currently, by using computers that facilitatesuch computations, it is possible to upgrade any measurement software in order to reachgreater accuracy and better outputs.7.4 Measurement MethodsThe different measurement methods for suspended bed load or total load areclassified as direct (or in situ) and indirect. Table 7.3 shows, in a simple way, suchmethods.Table 7.3 – Methods for gaging bed sediment (Carvalho, 1994)SedimentdischargeSuspendedsedimentdischargeMeasurementDirectDescriptionUses equipment that measures theconcentration or any other value, suchas turbidity or ultrasound directly in thestreamThrough sediment accumulation in ameasurer (graduated test tube)Measurement equipment ormethodologyNuclear measurer (portable orfixed), Optical ultrasonic flowmeter, Doppler Ultrasonic Flowmeter, Turbidimeter (portable orfixed)ADCP (Doppler)Delft Bottle (punctualmeasurement and highconcentration)Several kinds of equipment: -pumping, equipment using bottlesor bags, being punctualinstantaneous, punctual throughintegration and verticalintegrators (in Brazil, the North-American series– U-59, DH-48,DH-59, D-49, P-61 and bagsampler are the mainly ones thatare used)IndirectSediment collection by sampling of thewater-sediment mixture, concentrationand granulometry analysis and furthercomputation on sediment dischargeANEEL – Brazilian Electricity Regulatory Agency / SIH – Hydrologic Studies and Information Department17
Page 1 and 2: BRAZILIAN ELECTRICITY REGULATORY AG
Page 3 and 4: Reservoir Sedimentation Assessment
Page 15: Reservoir Sedimentation Assessment
Page 67 and 68:
Reservoir Sedimentation Assessment
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101:
show all

RESERVOIR SEDIMENTATION ASSESSMENT GUIDELINE - Aneel

Create successful ePaper yourself

Delete template?

Save as template?