Water Resource Sustainability Issues on Tropical Islands December, - - PowerPoint PPT Presentation

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Water Resource Sustainability Issues on Tropical Islands December, - - PowerPoint PPT Presentation

Oct 21, 2023 143 likes •847 views

innovation through engineering and scientific excellencesince 1985 Robert Bourke, Natalie Waters, and Jordon Moniuszko Water Resource Sustainability Issues on Tropical Islands December, 2015 Estuary Rehabilitation Stream Flow

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…innovation through engineering and scientific excellence…since 1985

Robert Bourke, Natalie Waters, and Jordon Moniuszko

Water Resource Sustainability Issues on Tropical Islands

December, 2015

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Estuary Rehabilitation Stream Flow Restoration to

Kaelepulu Estuary

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Kailua Bay

1,000 BC

1 Km

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Kawai Nui Swamp Kaelepulu Pond Kailua Bay

1928

1 Km

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Kawai Nui Swamp Kaelepulu Pond Kailua Bay Kaelepulu Pond Kawai Nui Swamp

1928

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1952

1 Km New Channel

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1952 1966

1 Km

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1952 1966

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1952 1966 1990

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1958

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ESTUARY CHALLENGES

  • EXCISED FROM

HEADWATER FLOWS

  • DECREASED

STREAM MOUTH EXCHANGE

  • BATHYMETRY

CHANGES

  • URBAN STORM

WATER FLOWS

  • INVASIVE

SPECIES

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ESTUARY CHALLENGES

  • EXCISED FROM

HEADWATER FLOWS

  • DECREASED

STREAM MOUTH EXCHANGE

  • BATHYMETRY

CHANGES

  • URBAN STORM

WATER FLOWS

  • INVASIVE

SPECIES

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ESTUARY IS ONLY EXPOSED TO TIDAL FLOW ON A PERIODIC BASIS MANUAL OPENING OF STREAM MOUTH ON ~MONTHLY SCHEDULE BY C&C HONOLULU

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Total Tidal Inflow 0.23 M cuft

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Total Tidal Inflow 21x103m3 Total Tidal Inflow 0.23 M cu ft Total Tidal Inflow 0.75 M cu ft Timing of Stream Mouth Opening to Maximize Initial Outflow Results in an Increase of Total Exchange

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ESTUARY CHALLENGES

  • EXCISED FROM

HEADWATER FLOWS

  • DECREASED

STREAM MOUTH EXCHANGE

  • BATHYMETRY

CHANGES

  • URBAN STORM

WATER FLOWS

  • INVASIVE

SPECIES

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SHOALING OF STREAM CHANNEL AT POND OUTFLOW INHIBITS TIDAL FLOW OF SALT WATER TO THE POND

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ESTUARY CHALLENGES

  • EXCISED FROM

HEADWATER FLOWS

  • DECREASED

STREAM MOUTH EXCHANGE

  • BATHYMETRY

CHANGES

  • URBAN STORM

WATER FLOWS

  • INVASIVE

SPECIES Being addressed through

State TMDL City NPDES

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ESTUARY CHALLENGES

  • EXCISED FROM

HEADWATER FLOWS

  • DECREASED

STREAM MOUTH EXCHANGE

  • BATHYMETRY

CHANGES

  • URBAN STORM

WATER FLOWS

  • INVASIVE

SPECIES

A 2004 ELRA $24K – 319 Grant B 2009 KCC $29K – Hi. Comn. Foundation & Castle Foundation C 2016 (?) C&C $750K State funded

A B C

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Of the principle problems confronting the estuary:

  • Pollutant flows from urban storm drains
  • Poor salt wedge penetration into pond
  • Poor exchange at stream mouth
  • Invasive Species (mangrove)
  • Lack of sufficient water flow

Improving water flow was deemed likely to provide the greatest benefit with the least effort.

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2.0 1.0 22.5 1.0

NOTE: All volumes given in millions of cubic feet

Estuary Area – 526,300m2 135 acres Volume – 750,000m3 = 26.5 Mft3 Volume of 8-inch (0.2m) tidal inflow – 106,000m3 = 3.7 Mft3

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CLASSICAL SALT WEDGE AND EXCHANGE CURRENTS IN AN ESTUARY

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Lanikai Bridge (Kbay Tide) Water Height Ft. MLLW

1 2 3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Feet MLLW

Lanikai Bridge Water Turbidity

10 20 30 40 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Turbidity NTU

Lanikai Bridge Water Salinity

10 20 30 40 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Salinity PPT

Kaelepulu Rain per Hr

0.2 0.4 0.6 0.8 1 1.2 1.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Days, Beginning Dec. 18, 2010

Rain Inch/Hr.

A B C D

DEPTH

TURBIDITY SALINITY RAIN

6 M cu ft

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PHYSICAL WATER QUALITY TRANSECTS OF ESTUARY CONDUCTED BEFORE AND AFTER EACH STREAM MOUTH OPENING EVENT T, Salinity, pH, NTU, Chl-a, PC, DO% @ 15 cm 30 cm 60 cm 120 cm 180 cm

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Beach Pond Channel

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Beach Pond Channel Shallows

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9/15/13 Salinity Kawainui Pre Opening 9/15/13 Salinity Kaelepulu

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9/26/13 Salinity Kawainui Post opening 9/26/13 Salinity Kaelepulu

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11/16/13 Salinity Kawainui – Pre opening 11/16/13 Salinity Kaelepulu

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9/15/13 Oxygen Kawainui Pre Opening 9/15/13 Oxygen Kaelepulu

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9/26/13 Oxygen Kawainui Post opening 9/26/13 Oxygen Kaelepulu

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11/16/13 Dissolved Oxygen Kawainui – Pre opening 11/16/13 Dissolved Oxygen Kaelepulu

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Salinity for 10 Sampling Events

Other Parameters Tracked:

  • Temperature
  • Dissolved Oxygen
  • pH
  • Turbidity
  • PC
  • CHL-A
  • Volume Exchange
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% Exchange = (SF-SI) / (35-SI)

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% Exchange = (SF-SI) / (35-SI)

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PROPOSAL TO TEST FLOW RESTORATION BY INSTALING TEMPORARY SIPHON OVER LEVEE ~ 6 L/s

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2 ft3/sec  5.2 M ft3/Month  ~1 ft Rise (- Evaporation)

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2 ft3/sec  5.2 M ft3/Month  0.9 ft Rise (- Evaporation)

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Construction of Four 6-inch PVC Siphons over Levee

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TEST TRIAL IS HYPOTHESIZED TO DEMONSTRATE THAT THE FLOW RESTORATION WILL

  • Increase monthly water exchange in the Kawainui

Stream Channel thereby improving water quality

  • Increase volume and period of exchange with the
  • cean by enhanced opening head and flow

dynamics

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Experiment Duration Control Portion of Experiment Marsh Water Surface Rate of Fall = 0.20 inch/da Marsh Water Surface Rate of Fall = 0.2 to 0.34 inch/da

WATER SURFACE ELEVATION OF KAWAINUI MARSH SOURCE WATER

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WATER SURFACE ELEVATION OF KAWAINUI STREAM SHOWING STREAM MOUTH OPENING PERIODS

0.5 1 1.5 2 2.5 3

J F M A M J J A S O

Water Surface Elevation, Feet MLLW

Months, 2015

Kaelepulu Water Surface Elevation, 2015 Feet MLLW Syphons ON

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WATER SURFACE ELEVATION OF KAWAINUI STREAM WAS ABOVE FLOOD THREAT LEVEL ON THREE OCCASIONS

0.5 1 1.5 2 2.5 3

J F M A M J J A S O

Water Surface Elevation, Feet MLLW

Months, 2015

Kaelepulu Water Surface Elevation, 2015 Feet MLLW

Periodsof Increased Flood Threat due to High Water Surface Elevation

Stream Mouth Openings

Syphons ON

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WATER SURFACE ELEVATION OF KAWAINUI MARSH SOURCE WATER

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WATER SURFACE ELEVATION OF KAWAINUI MARSH SOURCE WATER

~ 3M cu ft Water Transferred Each Month

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3M cu ft

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FRESH WATER INFLOW SPREADS RAPIDLY ALONG THE SURFACE OF KAWAINUI STREAM AND DOWNSTREAM TOWARDS THE BEACH. VERTICAL MIXING OCCURS MORE SLOWLY MAINTAINING STRATIFICATION THROUGHOUT THE MONTH.

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FRESH WATER INFLOW APPEARS TO FLOW RAPIDLY ALONG THE SURFACE AND EITHER EVAPORATE OR SLOWLY MIX WITH LOWER WATER LAYERS AND MAINTAINING STRATIFICATION

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SYPHON INFLOW RESULTED IN GREATER STRATIFICATION OF THE ENTIRE STREAM

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DISSOLVED OXYGEN

REMAINED WELL BELOW 20% SATURATION IN THE KAWAINUI STREAM THROUGHOUT THE PERIOD OF INFLOW. D.O. WAS NOT DISTINGUISHABLE FROM CONTROL (NO SYPHON FLOW) CONDITIONS ABUNDANT MANGROVE ALONG THIS STREAM REACH ARE LIKELY RESPONSIBLE FOR THE LOW D.O.

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MANGROVE STANDS LINE THE CHANNEL WHERE DISSOLVED OXYGEN LEVELS ARE LOW

ABUNDANT MANGROVE ALONG THIS STREAM REACH ARE LIKELY RESPONSIBLE FOR THE LOW D.O.

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3 1

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Dr ain

Kawainui Marsh Kawainui

High Tide 2.0 ft

Low Tide 0.0 ft

Overflow Weir 2.0 ft Oneawa Canal Kawainui Stream 12” Pipe through Levee Level Control Drain pipe through levee from Kawainui Marsh to Kawainui Stream Level Control Drain pipe through levee from Kawainui Stream to Oneawa Canal

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QUESTIONS ?

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TRACE- CONTAMINANT STUDY BY USGS 41 SAMPLE SITES WITHIN ESTUARY 71 POLLUTANT TRACERS CAFFEINE FOUND AT 3 SITES

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TRACE- CONTAMINANT STUDY BY USGS 41 SAMPLE SITES WITHIN ESTUARY 71 POLLUTANT TRACERS CAFFEINE FOUND AT 3 SITES

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TRACE- CONTAMINANT STUDY BY USGS 41 SAMPLE SITES WITHIN ESTUARY 71 POLLUTANT TRACERS CAFFEINE FOUND AT 3 SITES