6. Wave Pool water level management report · MCU19/0117

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1.0 Introduction and Background
Tod Consulting has been engaged by Mark Bain Constructions to provide engineering advice on a
proposed wave pool at 90 Beach Road North Shore. The purpose of this report is to outline the
strategies proposed to manage the operational water level in the proposed wave pool.

The proposed pool will cover an approximate area of 4,000m2, and will vary from 0.0 to 1.5m in
depth. The pool will be contained within walls approximately 2.0m high above normal water levels
in order to retain the design wave heights. The operational tolerance for the water level within the
pool is +/- 100mm


2.0 Maintaining water levels in the pool
As noted above the operational tolerance for the wave pool is +/- 100mm. In order to maintain the
water level in the pool within this operational range it will be necessary to top the water level up
during prolonged dry periods and dispose of excess water during prolonged wet periods.

Using Bureau of Meteorology data on rainfall and evaporation rates we have calculated the
necessary disposal volume for the 95th percentile wettest day and month during any one year and
likewise determined the required top up volume based on 5th percentile driest month.

This information is tabulated in Appendix A & B. In summary (after operational tolerances are
allowed for):

    •   The worst month for the 95th percentile wettest month (March) results in a disposal volume
        of 1,448,000 Litres.

    •   The worst case of the 95th percentile wettest day results in a disposal volume of 840,000
        Litres.

The worst case scenario for the 5th percentile lowest rainfall month (January) (95% driest) results
in a demand volume for top up of 160,000 Litres, however the cumulative effect of consecutive dry
months (Oct-Feb) comes to 329,600 litres.

Geotechnical investigations and testing have revealed that the existing ground conditions for the
site consist mainly of sands with a hydraulic infiltration rate of 1.5m per day (62.5mm/hr).

As such it is proposed to install one or more water tanks with natural ground base to dispose of any
surplus pool water via ground infiltration. The water from the pool will pass through a dosing process
to neutralise any chlorine or salt treatment used for the pool water prior to it being placed into the
water tank for infiltration into the ground. Based on our analysis we believe that a single tank 12m
in diameter and 2.5m high (capacity of 280,000 litres) will be enough to maintain the water levels at
operational levels for all but a few days of the year during the 95th percentile wettest conditions.
Should the pool operator wish to reduce the number of “down days” then a second tank could to
provided. Note the average infiltration volume for a 12m diameter tank equates to 169,000 litres/day.

To cater for the driest periods, again a single tank of a similar size (with a sealed base) will be
enough to cater for the majority of the 5th percentile driest months. However as noted above should
cumulative dry months occur consecutively then there is a risk that the water level in the pool could
drop below the operational level for an extended period (more than one month). As such a second
tank may be considered necessary.

As noted in the introduction the pool will have 2m high sides to retain the proposed wave, as such
up to 2m of rainfall can occur without the pool over topping. This represents almost an entire year
of rainfall for the 90th percentile wettest conditions. As such and based on the proposed disposal
method for excess water noted above the disposal of excess water can be easily managed without
the need for any emergency overflow weir.

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3.0 Conclusions and Recommendations
As noted above we have demonstrated that the water levels in the wave pool can be successfully
and simply managed using two 280,000 litre water tanks, one with an unsealed base for disposal
of excess water via infiltration and one for storage for top up during dry periods. This may still result
in some “down” days where the water level in the pool exceeds the operational tolerance level, so
there is an option to double the number of tanks to reduce (or virtually eliminate) any “down” days.




Doug Reynolds, Director – Civil Group
PREQ 9072
07 5449 9600 | [email protected]
TOD consulting engineers




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Appendix A: 95% Wettest Rainfall and Evaporation Rates




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[OCR of page images]
Appendix A: 95% Wettest Rainfall and Evaporation Rates

NOOSA NORTH SHORE WAVE POOL - WATER LEVEL MANAGEMENT

Location Noosa Heads, QL, AUS
DataSource http://www.bom.gov.au/watl/evaporation/
http://www.bom.gov.au/jsp/ncc/climate_averages/rainfall/indexjsp

 

95th %ile
Surf Pool Area (m2) 4,000

Annual
Evaporation (mm) 1,265
Evaporation (L) 5,060,000

95% Rainfall (mm) 2,344
Rainfall (L) 9,376,000

Net Rain(+)/Evap(-) ** 4,316,000 (+)
(varies monthly)
less operational tolerance (100mm)

net disposal volume required (worst month)

Monthly
Jen Feb Ma Apr May Jun Jul Aug Sep Oct
150 150 125 #0 50 50 2 80 100 125
600,000 600,000 500,000 320,000 200,000 200,000 320,000 320,000 400,000 500,000

340 527 587 293 255 262 195 229 16 403
1,360,000 2,108,000 2,348,000 1,172,000 1,020,000 1,048,000 780,000 916,000 660,000 1,612,000

760,000 1,508,000 1,848,000 852,000 820,000 848,000 460,000 596,000 260,000 1,112,000
400,000

1,448,000 Litres

** note annual rainfall is not total of individual months but represents the 95%ile annual figure
** Does not take into account losses from: filtration backwash; bather splash or carry-out; and, airborn mist created from breaking waves.

Daily Maximum
SurfPool Area (m2) 4,000

Daily Max Rainfall (mm)
Less Operational tolerance (+/- 100mm)

Net excess (mm)

Net Excess (Litres)

Wors Case 840,000 Lites
Next worst 608,000 Litres

Daily
Jen Feb Ma Apr May Jun Jul Aug Sep Oct
181 252 189 161 152 84 4 310 5 233
100 100 100 100 100 100 100 100 100 100

81 152 89 61 52 210 133
324,000 608,000 356,000 244,000 208,000 o 0 840,000 0 532,000

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Nov
125
500,000

204
816,000

316,000

Nov
135
100
35
140,000

TOD

engineers & project managers

TODE

engineers & project managers

600,000

262
1,048,000

448,000

100

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Appendix B: 5% Driest Rainfall & Evaporation Rates




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[OCR of page images]
TOD

engineers & project managers

Appendix B: 5% Driest Rainfall & Evaporation Rates

 

NOOSA NORTH SHORE WAVE POOL - WATER LEVEL MANAGEMENT
Location Noosa Heads, QL, AUS
DataSource http:/Awww.bom.gov.au/watl/evaporation/ . "
hittp:/ Awww.bom.gov.au/jsp/ncc/climate_averages/rainfall/indexjsp engineers & project managers
Sth %ile
SurfPool Area (m2) 4,000 Monthly
Annual Jan Feb Ma Apr May Jun Jul Aug Sep Oct Nov Dec
Evaporation (mm) 1,300 150 150 125 8 50 50 8 80 100 125 125 150
Evaporation (L) 5,200,000 600,000 600,000 500,000 320,000 200,000 200000 320,000 320,000 400,000 500,000 500,000 600,000
5% Rainfall (mm) 1,090 as 10 412 94.1 333 48.8 B7 22 1 39 22.4 12 32
Rainfall (L) 4,360,000 40,000 164,800 376,400 133,200 195,200 94,800 8,800 4,000 15,600 89,600 48,000 128,000
Net Rain(+)/Evap(-) ** -840,000 (_) -560,000 ~435,200 -123,600 -186,800 4,800 -105,200 -311,200 -316,000 -384,400 ~410,400 -452000 ~472,000
(varies monthly)
Less Operational Tolerance 400,000 400,000 400,000 400,000 400,000 400,000 400,000 400,000 400,000 400,000 400,000 400,000
cumulative shortfall (Oct-Feb)
Shortfall = -329,600 litres -160,000 -35,200 -10,400 -52,000 -72,000

** note annual is not total of individual months but represents the 5%ile annual figure
** Does not take into account losses from: filtration backwash; bather splash or carry-out; and, airborn mist created from breaking waves.

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