Hydrographic Survey Instructions –01/2021.
Necessary approval of schemes, provision for repair/AMC of survey / communication equipment has been provided in the sub-estimates. It is to be ensured that before commencement of seasonal works all equipment required for Automatic Hydrographic Survey System are in working condition.
Regional offices of IWAI are responsible for up keeping of all the instruments in working condition. For this, all instruments are to be properly maintained through AMC / timely repair. Every instrument shall be affixed with barcode stickerfor centralized asset monitoring. For any equipment, if the cost of repair / AMC exceeds the delegated power of field in-charge, necessary approval may be obtained from the H.O.
Necessary approval of schemes, work orders etc. for execution of different developmental activities for improvement and maintenance of LAD have already been issued from time to time. Now for getting better results, proper surveys and monitoring of the works are necessary.
Accordingly, the following instructions are issued with immediate effect for strict compliance by all field offices:
Operational instructions before Start of survey:
• Survey launch / Boat should be checked that it is “fit for survey”
• All the equipment / PC’s are to be checked for its working conditions and arranged in order so that these are free from any damage / impact
• All the equipment are properly connected and interfaced
• Power Supply is as per equipment standard (input / output). Follow standard procedure for “Switching On / Off”
• Ensure that positioning equipment has received sufficient number of satellites for giving position and meets IHO accuracy standard.
• Draught of the Echosounder should be accurately measured and checked with “BAR”. Bar Check should be carried out for different depths prior to commencement of survey, end of survey and compared as the survey progresses, as a check against gross errors.
• Datum (WGS84), Projection (UTM), Zone number should be properly entered
• Check that equipment are properly attached in respective Ports of Computer and digital outputs are properly being received with survey software
• Previous surveyed route of the same area / stretch should be available as reference lines / track for guidance
• The thalweg survey rout shall be made available to all Mobile RIS stations, control stations.
• All the data transmitted from equipment is to be recorded, so that chart can be plotted in any desired scale
• Project name should indicate fortnight, month, year and stretch
• PC should be loaded with latest digital chart / RNC (.dxf base chart)
• All survey PC’s should be equipped with CD / DVD Writer / USB drive and all survey data to be duly annotated, stored and kept in a safe place. All survey data should also be stored in back-up server. PC should be loaded with proper anti-virus software and anti-virus definition.
Data to be recorded during survey:
• Details of all topographical features of importance to river mariners are to be collected for Charting (new object) or verification (Charted object). Any significant developments like new structure, HT line / cables, bank erosion, formation / removal of sand bars, other navigation impediments etc. are to be updated during thalweg survey.
• Way Points are to be created, whenever passing known points which are identifiableon the ground and in the chart like bridges, power line, telephone lines, towers, chimneys, buildings, trees, etc.
• Hydrographic Surveyor’s in the respective stretches must ensure that navigable channel (deepest route) is identified at shoal locations by taking sufficient cross-sections so as to ensure corrections of LAD at the locations before issuing River Notices / LAD Report.
• On completion of thalweg survey, Electronic chart is to be updated if any required. The shoal formation and nav aids are to be updated in the electronic charts.
• LAD data is to be timely updated in the LADIS Portal and latest nav route in the form Hypack data is to be uploaded in PANI portal.
• Based on the analysis of shoals during previous year’s record and also when water level reducing, shoals are to be identified while doing thalweg survey and conduct recky survey by taking cross sections at shallow areas and also in secondary channels in the stretch. Secondary channel is to be surveyed once in a month while conducting thalweg survey.
• Channel should be closely monitored when the depth reaches 0.5m above the targeted LAD. After identification of the shoal limits and before further drop of LAD, detailed survey should be conducted at shallow patch covering 500 mts. U/S and D/S of theidentified shoal. Cross section is to be carried out at 50m interval for bandalling surveys and at 25m interval for dredging surveys.
• Before commencement of pre dredging/ bandalling survey, Water level data is to be collected by setting up of a tide pole in the survey area,connect it to a TBM at nearby location and later it should be connected to B.M. in the area w.r.t. (M.S.L.). Gauge reading should be taken at least twice in a day at 8 A.M. and 4 P.M. till the completion of post dredging / bandalling survey.
• Transfer of sounding datum is to be carried out as per (Admiralty manual for Tides).If established datum is available nearby, interpolation method is to be followed for arriving at datum value at site.
• Observations such as position of bed sample, water sample; data in respect of wind speed, current measurement, discharge, flow direction, fixing of sand churs, snags, Bandals, dredging alignment, channel marks, night navigation lights and other prominent features on the bank should be collected during detailed survey and incorporated in chart.
• Wherever the depth is less and can’t be measured with EchoSounder, it should be carefully measured with calibrated sounding pole.
• There should not be any data gap. If there is any data loss due to replacement of GPS batteries or any other reason, vessel should be slow down & turned around. Data logging to be resumed from the last recorded location.
REPORT OF SURVEY
• All the soundings should be carefully edited for false echoes and corrections be merged.
• Positions be corrected for false and wrong positions.
• Pre & post dredging charts should be submitted to H.O. immediately. Detailed quantity calculation sheets w.r.t. the design channel should be attached with the chart.
• Water level data should be indicated on the detailed survey chart for analysis purpose. Charts should also have the description of B.M. & TBM etc. for easy recovery in future. Chart should be signed by the survey team-in-charge, In-charge of survey & Director / Office In-Charge.
• Soft copy of Raw, Edited & Sort data of each survey should be submitted to H.O. along with the chart immediately on completion of survey.
• Digital charts (base charts) should be updated withlatest thalweg route and detailed surveys.
• LAD Report and River Notices should reach H.O. within 48 hours via E-mail/FAX/Courier after completion of Thalweg survey.
ADCP, Side Scan Sonar and Sub-Bottom Profiler
Data collected from survey equipment like ADCP, Side Scan Sonar & Sub-Bottom Profiler are necessary for making of updatesinRNC / ENC, River Pilot and also to study the behavior of the Navigational channel. Hence the following works should be undertaken:-
a. Velocity & discharge measurement using ADCP at all tide gauge locations once in a month and also during terminal surveys
b. Velocity & discharge measurement using ADCP at every 50Km interval during flood season
c. Use of ADCP, Side Scan Sonar and Sub-Bottom Profiler at Baghmari Siphon in Farakka Feeder Canal (Haldia -Farakka stretch)
d. Use of Side Scan Sonar and Sub-Bottom Profiler for identification & searching of submerged objects & for terminal surveys.
e. Locations of river bed with hard strata should be identified and marked using Sub-Bottom Profiler
f.Any other specific requirement