MODULE 5

Site Selection and

Security Considerations

Mark HeggliInnovative Hydrology, Inc.

Consultant To The World BankExpert Real-Time Hydrology Information

Systems

Examples that refer to products are intended for illustrative purposes only, and do not imply an

endorsement or recommendation of any particular product

Site Selection and Security Consideration

Site selectionDefine the Site PurposeSite Survey/ Field Visit

Security considerations for all sites

Site Selection:

Define The Site Purpose Establish the purpose of the site

What are you trying to measure?○ Water Level○ Discharge○ Water Temperature○ Water Quality○ Rainfall○ Other

How crucial is the data?○ Logging needs○ Frequency of Data Collection

Consideration of future needsAdditional sensors, additional telemetry

Site Selection:

Site Survey/Field Visit Why is it important to complete a site survey?

Ease and safe accessibilityUnderstand the characteristics of the area being

measured○ Understanding the characteristics will help in the

decision making of proper equipment to make accurate measurements

○ A mismatch between local conditions and appropriate technology can result in:Poor quality of dataHigh maintenance requirements for both field and office

procedures

Site Survey/Field Visit:

Accessibility and Safety Safe access to site

Road to DriveWalking PathBoatAircraft

Minimization of risk during install, ongoing operation and maintenancePersonnel, sub-contractors, public

Site Survey/Field Visit:

Water Level and Discharge Sites Stream characteristics

ControlUpstream and downstream considerationsContained and subterranean flowStreambed and banksGauging sections

Stream Characteristics:

Control

What is a control? Control needs to be stable

and sensitive • Minimum change in

discharge with minimum change in stage

• Cease to flow point should not be affected by sedimentation or weed growth

• Try to find a site with an existing natural control

Types of Control Natural control Man made control

Stream Characteristics:

Upstream and Downstream Considerations

Straight section of stream According to the WMO, the general

course of the stream is straight for about 10 times the stream width, upstream and downstream from the gauge site if the control is a river reach (channel control).

Approach velocities are evenly distributed

Minimize possibility of sedimentation fill

Downstream Effects Evaluate downstream effects

( tidal effects, water shortages, future civil works/dams)

Stream Characteristics:

Contained and Subterranean Flow

Contained FlowSection needs to contain all

flow including maximum flood flow

No possibility of over bank or side channel flow

Subterranean FlowEvaluation should include

possibility of subterranean upstream, causing bypassing of flow (prevalent in underground mining areas)

Stream Characteristics:

Stable Stream Bed and Banks Stable Stream Bed

Minimal infill or scour Stable Stream Banks

Avoid locations with bank scour or erosion

Stream Characteristics:

Gauging Sections Gauging Sections

Feasibility ○ Low flow wading ○ Boat measurement○ Unmanned cableways

Rainfall Site Selection

Obstruction Wind Slopes Height of gauge

Wind velocities increase with heightHigh enough to prevent splashing from the

ground1 m is standard according to WMO

Site Selection:

Location of Instrumentation Power

AC DC- Generator or Battery

• Solar needs a clear access to sunlight Telemetry

Landline GPRS/GSM Coverage Radio Link Satellite Access

Housing of Equipment Location of instrumentation must be above

maximum flood

Security Considerations

All SitesLocksFencingDisguise

Suggestions Rarely will an ideal site be found for a gauging

station and judgment must be exercised in choosing between adequate sites, each of which may have some shortcomings

Often adverse conditions may exist at all possible sites for installing a required gauging station and a poor site must be accepted. For example, all streams in a given region may have unstable beds and banks, which result in continually changing stage-discharge relations.

QUIZ

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QUIZ

Thank You WMO Site Selection 1044 Volume 1 The ideal gauge site satisfies the following criteria, many of which are defined in ISO 1100-1:

(a) The general course of the stream is straight for about 10 times the stream width, upstream and downstream from the gauge site if the control is a river reach (channel control). If the control is a section control, the downstream conditions must be such that the control is not drowned. The water entering a section control should have low velocity (see (f) below);

(b) The total flow is confined to one channel at all stages and no flow bypasses the site as subsurface flow; (c) The stream-bed is not subject to scour and fill and is relatively free of aquatic vegetation; (d) Banks are permanent, high enough to contain floods, and are free of brush; (e) Unchanging natural controls are present in the form of a bedrock outcrop or other stable riffle for low flow and a

channel constriction for high flow – or a waterfall or cascade that is unsubmerged at all stages. If a natural control is not available, then channel conditions should allow for the construction of an artificial control such as a weir or flume (see Chapter 3);

(f) A pool is present upstream from the control at extremely low stages to ensure a recording of stage at extremely low flow, and to avoid high velocities at the streamward end of stage recorder intakes, transducers, or manometer orifice during periods of high flow. The sensitivity of the control should be such that any significant change in discharge shall result in a measurable change in stage;

(g) The gauge site is far enough upstream from the confluence with another stream or from tidal effect to avoid any variable influence the other stream or the tide may have on the stage at the gauge site;

(h) A satisfactory reach for measuring discharge at all stages is available within reasonable proximity of the gauge site. It is not necessary for low and high flows to be measured at the same stream cross-section;

(i) The site is readily accessible for ease in installation and operation of the gauging station; (j) Within reach of a suitable telemetry system; (k) Good conditions for discharge measurements at all stages; (l) Instruments, shelter, and housing above all flood levels. Sensors with a range to measure floods and drought.

Rarely will an ideal site be found for a gauging station and judgment must be exercised in choosing between adequate sites, each of which may have some shortcomings. Often adverse conditions may exist at all possible sites for installing a required gauging station and a poor site must be accepted. For example, all streams in a given region may have unstable beds and banks, which result in continually changing stage-discharge relations.