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HYDROMETRIC SITE INSTALLATION TECHNIQUES. Training - PNG Power Port Moresby July 2012. STREAM SITES – Float. General Requirements. Must not effect approach conditions to control. Must be stable in all weather conditions. Must be large enough to eliminate fouling of float and counterweight.
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HYDROMETRIC SITE INSTALLATION TECHNIQUES Training - PNG Power Port Moresby July 2012
STREAM SITES – Float General Requirements Must not effect approach conditions to control Must be stable in all weatherconditions Must be large enough to eliminate fouling of float and counterweight Must be above predicted maximum flood level
Intake Pipe Stream Bank Installations – 2 pipes required Minimum internal area of each intake = approx 1/1000th of internal area of the float well All joints must be waterproof Intakes must be a minimum of 150mm below CTF and 300mm above the invert of the well Must be laid on a stable foundation In Stream Installations – slots or holes in well are OK
Static Tube Used where velocity of flow causes drawdown effect or ‘pile-up’ of water in the stilling well Positioned at right angles to the flow Water enters through pre-drilled holes in tube End of the tube is capped
Instrument Shelter Type of instrumentation Site security and accessibility Local environment Project budget
STREAM SITES – Pressure Closed System ‘Hydrostatic’ System
Open System Dry nitrogen or air is bubbled at a pre-set rate to the stream Back pressure sensed by transducer is converted to water level
Submersible Sensor System Electronic pressure sensor submersed in stream ‘MUST’ be referenced to atmospheric pressure, ‘Vented’ and ‘Non-Vented’ types Absolute Pressure = Gauge Pressure + Atmospheric Pressure
Orifice Installation Either encasement of the orifice in a concrete block OR supporting on galvanised pipe Orifice should be installed in close proximity to the prime gauge, however it must NOT be connected Orifice can be either a small diameter type (BU07) or Gas Chamber Orifice (GC01P)
Orifice Types • Traditionally, a small diameter capillary type to allow gas to bubble freely into the water column • Some limitations: • Siltation effects • Fast rising stage heights (‘lag’ problems) • Aquatic growth (non-copper type) • Large volume Gas Chamber Orifice (GCO) is commonly used where: • High sediment/silt content is prevalent • Fast rising stages can occur • Aquatic growth is prevalent • Lower bubble rate is needed
Pressure Tubing Either 6mm or 10mm OD nylon tubing used MUST be encased in a suitable conduit (e.g. Poly Pipe or GI pipe) from the Instrument Shelter to the orifice • Conduit MUST be secured to the stream bank by: • Trenching and backfilling • Masonry anchors to attach to bedrock • Fastening to large, stable tree trunks • Fastening to ground using metal stakes (e.g. star-pickets) Brass pressure fittings with nylon/brass ferrules MUST be used on all connections Number of connections must be kept to a minimum If distance from Instrument Shelter to orifice exceeds 150m, DUAL-LINE system should be installed
Pressure Tubing (continued) Tubing MUST be installed with continuous downward slope with NIL ‘low spots’ X Tubing MUST be encased from the instrument shelter to the orifice
Orifice Installation Orifice fitting secured in concrete block and lowered into position Orifice fitting secured using GI pipework framework
Staff Gauges Available in painted aluminium, steel or plastic • Can be secured by: • Fastening to timber gauge boards • Clamping to GI pipe • Fastening to vertical surfaces (e.g. bridge piers, stilling wells) • Fastening to galvanised ‘C’ section The prime gauge MUST be in close proximity to the orifice but NOT connected
Junction Pits Pressure line should run through a number of pits for ease of access Pits ideally should be a maximum horizontal distance of 50m apart, with a pit located near the orifice Pits should be made from a sturdy, non-corrosive material (e.g. fibrous cement, PVC etc with a removable lid) with location marked
Junction Pits (continued) Following installation, a survey must be made of pit locations For new sites, always install ‘pull-throughs’ to facilitate future upgrades
Gas Chamber OrificePerformance Test based on simulated rise of 9 metres per hour Minimal ‘lag’ up to a rise of 3 metres per hour
Station Benchmark If existing BM not available, a BM needs to established with an I.D. plate • Needs to be on a STABLE structure such as: • Rock shelf (Stainless steel pin with yellow triangle) • Tree (GI pin with yellow blaze) • New structure (concrete pad, float well etc) Preferable to tie into a known datum (e.g. AHD) ‘Assumed Datum’ is acceptable
Include Velocity Head Gauge Datum Cease to Flow – determined by leveling Gauge Pool Control Section Flow Deepest Point on Control Gauge Pool Control Section Perpendicular to Flow
Gauge Datum (continued) • Gauge Zero Definition: • Is the RL of the ‘Zero’ mark on the prime gauge • Gauge Zero Value MUST: • Ensure no ‘negative’ gauge heights during life of station • NOT be changed during life of station • Be regularly monitored (i.e. Annual Inspection)
Controls • Control Definition: • Is the physical feature in the stream, controlling the relation ship between Gauge Height and Discharge Artificial Control Natural Control
Extreme Conditions All civil works MUST be installed to withstand water of high velocity and turbulence
METEOROLOGICAL SITES Daily Read Rain Gauge Hole approx 300mm diameter and 230mm depth Bed of compacted fine gravel or blue metal Install outer enclosure and check for level Backfill with gravel, sand compact and re-check level Surround gauge with grass or mulch
Tipping Bucket Rain Gauge Ground Level Installation – fasten to flat surface Pole Mount Installation – gauge attached to a length of 80mm GI pipe into ground Roof Mount Installation – secure to flat or sloping roof
