KING COUNTY SONAR INSPECTION BALLARD TWIN SIPHONS

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KING COUNTY SONAR INSPECTIONBALLARD TWIN SIPHONS

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INTRODUCTION

• The Ballard twin siphons were constructed in the
  mid-1930s using wood stave pipe.
• The pipe is comprised of 21 creosoted wood staves
  of 2 inch by 6 inch stock, resulting in a nominal
  36 inch inside diameter.
• The survey was conducted from October 31st to
  November 3rd in 2005.

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SONAR SYSTEM

• The sonar system employed a 2.2 MHz rotating head
  sonar system.
• A gyro-stabilized attitude and acceleration
  navigation system was used to provide orientation
  and position data.
• Communication with the sonar carried via a fibre
  optic cable operated from a winch on the upstream
  (north) side of the siphon.
• A cable payout counter recorded the probe
  position as the instrument was moved through the
  siphon, and load cells monitored the amount of
  strain on each cable.

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ROTATING HEAD SONAR
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SCOPE OF WORK

• The project entailed carrying out a sonar
  profiling inspection of the Ballard siphons. The
  purpose of the inspection is to assess the
  condition of the wood stave pipe and to ascertain
  the level of sediment in the pipe.

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North Station Draw Works
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Sonar System Probe
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North Station Probe Launch
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Marco Marine (South) Station
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SURVEY RESULTS - West Siphon

• Cross-section change extending from 100 feet to
  150 feet.
• Abrupt change the 100 foot mark with a tapering
  of the effect at a distance of 150 feet.
• A peak value of 17.9 percent obstruction of the
  pipe over the nominal 36 inch equivalent is
  measured.

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SURVEY RESULTS - West Siphon
Distance 103.9 feet
Distance 152.9 feet
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3D View with Wood Stave Grid
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Ballard West 90 to 160
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SURVEY RESULTS - West Siphon

• 275 to 305 feet - percent obstruction value of
  10.8 percent.
• 425 to 480 range, with a peak obstruction of 19.8
  percent.

Distance 463.0 feet
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Ballard West 410 to 480
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SURVEY RESULTS - West Siphon

• 750 to 1035 foot range in the central area of the
  horizontal section.
• Percent obstruction in the 15 percent range, with
  a peak values in the 18 percent range.
• Calculated sediment volume of 834 cubic feet.

Distance 1002.1 feet
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SURVEY RESULTS - West Siphon

• A more subtle cross-section change in the 1205 to
  1220 foot range.

Distance 1205.7 feet
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SURVEY RESULTS - East Siphon

• Similar zonation to that observed in the west
  siphon.
• Debris 80 to 110 feet.
• Change in cross-section of the siphon from 115 to
  210 feet

Distance 128.7 feet
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SURVEY RESULTS - East Siphon

• The central horizontal run in the east siphon
  shows lesser debris accumulation
• East siphon carries only peak flows.
• Calculated sediment volume is 551 cubic feet.

Distance 800.1 feet
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Ballard East 760 to 830
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SURVEY RESULTS - East Siphon

• Cross-section change at 1195 to 1210 feet.
• Coincident with a similar feature on the west
  siphon.

Distance 1203.2 feet
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KING COUNTY SONAR INSPECTIONFREMONT TWIN SIPHONS

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INTRODUCTION

• The system consists of a nominal 59 inch siphon
  that carries the normal flows, together with a 47
  inch siphon intended to handle peak flows.
• The survey was conducted from November 28th to
  30th, 2005.

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SCOPE OF WORK

• The project entailed carrying out a sonar
  profiling inspection of the Fremont Siphons. The
  purpose of the inspection is to assess the
  condition of the siphons and to ascertain the
  level of sediment accumulation in the pipes.

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Fremont North Station
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Sonar System Probe 
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North Station Probe Launch
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South Station Draw Works
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SURVEY RESULTS - West Siphon

• Sonogram within forebay is shown here.
• The image shows the water level in the forebay as
  a central horizontal reflector.

Distance 10.1 feet
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SURVEY RESULTS - West Siphon

• Access riser pipe entering 47 inch siphon.
• Similar response is seen passing the riser pipe
  at the end of the traverse, at a distance of 463
  feet.

Distance 27.3 feet
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SURVEY RESULTS - West Siphon

• Clean cross section with no evidence of debris or
  sediment.
• North descending segment to 84 feet.
• Horizontal segment to 410 feet.
• End of survey at 465 feet.

Distance 152.5 feet
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SURVEY RESULTS - East Siphon

• East siphon (59 inch) carries the normal flows.
• A small degree of sedimentation at the 390 foot
  mark.

Distance 389.2 feet
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SURVEY RESULTS - East Siphon

• Except for the 390 foot zone, clean
  cross-sections with no evidence of sediment or
  debris.
• No anomalous pipe wall conditions were noted.

Distance 360.3 feet
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Fremont East 390
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KING COUNTYSONAR INSPECTIONHIGHWAY 520 SIPHON

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INTRODUCTION

• The sewer system consists of a 42 inch gravity
  pipe that carries the normal flows, together with
  a 108 inch siphon designed to handle peak flows.
• The survey of the Highway 520 Montlake Crossing
  Siphon was conducted on December 1st, 2005.

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SCOPE OF WORK

• The project entailed carrying out a sonar
  profiling inspection of the Highway 520 Montlake
  Crossing Siphon. The purpose of the inspection
  was to assess the condition of the 108 inch
  siphon and to ascertain the level of sediment
  accumulation in the siphon.

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South Station
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Sonar System Probe
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South Station Vault Entry
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North Station Draw Works
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SURVEY RESULTS

• Sonogram from the forebay

Distance 14.3 feet
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SURVEY RESULTS

• Clean section with no evidence of debris or
  sediment.
• No evidence of wall damage, pitting or erosion is
  seen.

Distance 48.6 feet
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SURVEY RESULTS

• Manhole entry at the 38 foot and 170 foot.

Distance 170.1 feet