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1 Water Balance & Management Strategy by Waqar Ahmed5 November 2009

Water Balance and Water Management Strategy

Waqar Ahmed

WPBG-Sharjah

5 November 20092 Water Balance & Management Strategy by Waqar Ahmed

• Definitions

• Water Balance for Airport Plot Abu Dhabi

• Objective

• Computations

• Water Re-Use / Management Strategy

• Conclusion (Project Based)

Water Balance & Management StrategyCONTENTS


Water Balance:

In Hydrology, Water balance means equating the inflows and outflows of a system

DEFINITIONS Water Balance & Management Strategy

Global Water Balance


Evapotranspiration:

It is sum of (water loss) through evaporation and transpiration

Where transpiration is evaporation of water from Ariel parts of plants



Water Balance:

I – O = ΔS/ ΔT

Where

I = Inflow including the Potable water and Reliable rainfall

O = Outflow including the Wastage, Evapotranspiration, Surface runoff, percolation and rain losses

ΔS = Change in storage

ΔT = Time



Water Balance for Airport Plot Abu Dhabi

Water Balance & Management Strategy


Water Balance for Airport Plot Abu Dhabi



The main objectives are:

• To compute a complete water budget for the project clearly showing the inflows provided and outflow generated

• To increase the landscape area by utilizing the surplus grey water

• To seek the possibility of a water feature using recycled surplus water even in the low irrigation demand month (winter season)

• Possible reduction in water demand by use of recycled water for toilet use

• Review of Rain Water harvesting for use

OBJECTIVE Water Balance & Management Strategy


• Surface Runoff

Where

Pe = Excess Rainfall (mm)

P = Reliable rainfall (mm)

CN= Curve Number (selected depending on the land uses 58.8)

S = Potential Maximum retention

• The twenty six years monthly rain fall data (1982-2007) has been analysed

• 50% reliability of the rain fall

Reliability Factor = no of years x % Reliability

COMPUTATIONS Water Balance & Management Strategy

SP

SPPe 8.0

)2.0( 2

101000

CN

S


• Irrigation Water Requirement

Where

IWR = Irrigation water requirement

ET0 = Evapotranspiration

Kc = Crop coefficient (Grass=1 and Tree=1.3)

A = Area to be irrigated

ETc = ETo x Kc x A

The evapotranspiration has been computed using version 4 of the CropWat software

COMPUTATIONS Water Balance & Management Strategy

8.00 AKcET

IWR


Water Balance & Management StrategyCOMPUTATIONS



Item Description Inflow Outflow Remark

m3 m3

Rainfall 11,558 50% reliable rain for AD Airport

Potable Water 3,681,720 Average annual demand

Wastage 920,430 25% Potable Water (Assumed)

Irrigation Water Use 1,096,077 29ha of landscape area in project

Runoff 1,223 For CN(1) = 58.8

Percolation 219,215 20% Etc

Rain Losses 10,333 Part of Rain not converted into Runoff

Total 3,693,278 2,247,278

Balance 1,446,000



Water Balance Variation

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Months

Bal

ance

Wat

er (

m3)



• The above water balance assumes a 100% onsite treatment of the wastewater and scenario is for full scale project development.

• Approximately 1.5 million cubic meters of water should be available on annual basis. Under a conventional scheme, these water will be lost in one or more of the following ways:

• Rejection into the drainage system

• Dumped into a water feature and evaporated

• Sold to a nearby development


MASTER PLAN Water Balance & Management Strategy


• Surplus amount of water is available to irrigate an additional area of 16.5 ha

• By using the grey water for the toilet purposes the potable water demand can be reduced by about 23%. However the use of TSE in this way would consequently reduce the amount of land available for irrigation

• The current mass balance allows for a provision of a recreational lake to take up the surplus water

• The reliable amount of rainfall runoff per annum is 1224 m3 and therefore does not warrant a storage structure alone, however this discharge could outfall into the irrigation lake (if built) subject to the provision of oil interceptors

INITIAL CONCLUSIONS Water Balance & Management Strategy


• Water Balance shows that significant amount of TSE is available annually

• In order to maximize the useful consumption of the surplus TSE it will be required to provide storage for retaining the TSE during the low demand and high consumption months

FURTHER COMPUTATIONS Water Balance & Management Strategy


Design Parameters.

a. The surplus TSE is that water that is available after irrigating the landscaped areas (within project boundary)

a. The onsite irrigation storage tank has been sized for storing one day onsite irrigation demand so will not be considered for retention storage.

b. Recycling of a part of TSE for toilet use has not been considered in this water balance

c. The evaporation (EW) from the storage pond has been estimated on the basis of pan evaporation data available for Abu Dhabi International Airport

d. The irrigation water demands have been computed on monthly basis on the basis of monthly Evapotranspiration (ETO) rates computed by an industry standard software CROPWAT

FURTHER COMPUTATIONS Water Balance & Management Strategy


WATER REUSE STRATEGY-OPT 1 Water Balance & Management Strategy

Ponds DetailsIrrigation

Water Use

Evaporation

Spill Irrigation Area

No Area(ha) Vol. (m3) (m3) % (m3) % (m3) %

Open Space in Plot (ha)

Outside Plot (ha)

1 2.85 114,000 804,234 56 94,734 6.5 433,028 30 29.9 25

2 6 240,000 965,081 67 182,349 13 58,566 4 29.9 30

3 8.6 344,000 1,061,589 73 280,486 20 0 0 29.9 33

Constant pond depth of 4m


WATER REUSE STRATEGY-OPT 2 Water Balance & Management Strategy

Ponds Details Irrigation Water Use Evaporation Spill Irrigation Area

No Area(ha) Vol. (m3) (m3) % (m3) % (m3) %

Open Space in Plot (ha)

Outside Plot(ha)

Many 23 344,000 257,355 26.6 710,686 73.4 0 0 18.4 8

Constant pond depth of 1.5m


CONCLUSIONS Water Balance & Management Strategy

Option Pro’s Con’s

Deep Ponds (4m) More irrigation can be provided to the landscaping outside the plot (33ha max)

Does not provide water feature aesthetics and vision.

Shallow Ponds (1.5m) Provides water feature aesthetics and vision.

Increase in evaporation reduces water available for irrigation of the landscaping out of plot to 8ha.


QUESTIONS


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