Instrumentation and monitoring of Dams and Reservoir

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INSTRUMENTATION &

MONITORING OF DAMS &

RESERVOIRS

SUJAY RAGHAVENDRA N12WR10F

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OVERVIEW 

Introduction.

Purpose of instrumentation & monitoring.

Instrument: Types and usage.Pore pressure & uplift pressure.

Water level & flow.

Seepage flow.

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Introduction

For the safety & normal operations of a dam, preciseinformation is required from instrumentation &monitoring of  dam’s body, the surrounding

foundations, the reservoir & river basin.Their behaviour during each stage of investigation,design, construction, & operation are very importantinformation for engineering decisions.

Different kinds of instrumentation & monitoring arerequired for different types of dam, reservoir & riverbasin.

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Purpose for instrumentation &

monitoringEvaluation of dam performance compared to design &expectations.

Early warning of changes that could affect the integrityof the dam.

Increase knowledge of dam behaviour.

Investigation & diagnosis of abnormal damperformance.

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Instrument: Types and usage

A wide variety of devices and procedures are used tomonitor dams. The features of dams and dam sites mostoften monitored by instruments include:

pore pressure and uplift pressures

water level and flowSeepage & leakage flow

water quality

temperature

crack and joint sizeseismic activity

weather and precipitation

stress and strain

movements (horizontal, vertical, rotational and lateral) 5

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Pore Pressure & Uplift Pressure

A certain amount of water seeps through, under, andaround the ends of all dams. The water moves throughpores in the soil, rock, or concrete as well as throughcracks, joints, etc. The pressure of the water as it

moves, acts uniformly in all planes and is termed porepressure.

The upward force (called uplift pressure) has the effectof reducing  the effective weight of the downstream

portion of a dam and can materially reduce damstability.

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Pore pressures can be measured with the followingequipments.

Piezometers

electrical

pneumatic

hydraulic

porous tube

slotted pipePressure meters and gauges

Load cells

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POROUS TUBE PIEZOMETER.

This is a open stand pipe- typepiezometer.

Open standpipe piezometersare also known as Casagrande-type piezometers

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OBSERVATION WELLS 

Observation wells are appropriate only in auniform, pervious material.

The depth to the water level is measured bylowering an electronic probe or weighted tape into

the pipe.

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Water Level and Flow

For most dams, it is important to monitor the waterlevel in the reservoir and the downstream poolregularly to determine the quantity of water in thereservoir and its level relative to the regular outletworks and the emergency spillway.

The water level is also used to compute water pressureand pore pressure; the volume of seepage is usually

directly related to the reservoir level.

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Water levels may be measured by

simple elevation gauges—either

staff gauges or numbers painted

on permanent, fixed structures inthe reservoir or by complex

devices that sense water levels.

Flows are often computed from aknowledge of the dimensions of 

the outlet works and the depth of 

flow in the outlet channel or pipe.

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Cont’d.. 

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SEEPAGE & LEAKAGE

Seepage is defined as interstitial movement of waterthrough a dam, the foundation, or the abutments.

It is differentiated from leakage, which is flow of waterthrough holes or cracks.

Monitoring the seepage that emerges downstream isessential in assessing the behaviour of a dam during its firstfilling.

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Seepage may be measured using the followingmethods:

Weirs (any shapesuch as V-notch,

rectangular,trapezoidal)

Flumes (such as aParshall flume)

Pipe methodsTimed-bucketmethods

Flow meters

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Instrumentation monitoring program established atone dam may not be appropriate at another dam

Each project be independently evaluated.

Monitoring performance with instruments &

measurements permits comparison of constructedreality with design estimates & may help explaindifferences between them.

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“Dam safety guidelines., Part 4: Investigations,monitoring & surveillance of  dams”., AucklandRegional Council.

“Engineer manual: 1110-2-1908,Instrumentation of embankment dams andlevees”., Department of the army. U.S. Armycorps of engineers

“Chapter 6: Instrumentation and MonitoringGuidelines”, Texas commission onenvironmental quality.

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THANK YOU

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