artificial infiltration of roof rainwater in dhaka...

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com November 2016, Volume 4, Issue 11, ISSN 2349-4476

161 SHAHAB UDDIN and Dr. Md. Akramul Alam, Md. Parvej

Artificial Infiltration of Roof Rainwater in Dhaka City

SHAHAB UDDIN1 and Dr. Md. Akramul Alam

2, Md. Parvej

3

1Student at Dhaka University of Engineering & Technology; DUET

2 Professor at Dhaka University of Engineering & Technology; DUET 3Student at Dhaka University of Engineering & Technology; DUET

ABSTRACT

The issue of rainwater is gaining more and more importance for developing countries especially in Dhaka city of

Bangladesh, where poor and least rainwater management is one of the main causes for environmental pollution, water

logging and lowering the ground water table (about 2m-3m per year). The dwellers of Dhaka city are in dilemma for

both waterlogging problem and lack of groundwater. The built-up areas in Dhaka city have increased 210.37% from the

year 1960 – 2014. In 2013 the quantity of greeneries was about 0.13 acre for 1000 people. Such condition provides vital

obstruction in infiltration of rainwater which finally affects the ground water table and also water logging in Dhaka city.

The study has attempted to observe a model of artificial infiltration well for groundwater storage capacity. Rainwater

intercepted in the buildings will be passed into the aquifer by gravity action and will enrich ground water storage. The

model of artificial infiltration well was installed in DUET campus. Three experiments at different pressure head (170,

156.5 and 146) feet on the model were tested for observing storage capacity of aquifer. After determining the

permeability of soil, theoretical storage capacity of well was determined by Darcy’s Law.

The average permeability of soil was 0.088m/min. Actual and theoretical ground water storage capacity were

0.01095m3/min and 0.0159m

3/min at170 feet pressure head respectively. The groundwater storage equation was got as

Q=0.687*K*(H/L)*As. Environmental impact from rainwater will be minimized and ground water table will rise in

notable scale.

The main purpose of this study is to discuss water related problem in Dhaka city as like water logging, groundwater

depletion and solution of those problems by a low cost technology of artificial infiltration system of roof rainwater by

wells.

Keywords:

Rainwater, Waterlogging, Infiltration, Gravity action.

INTRODUCTION

Dhaka faces acute water crisis. Groundwater tables

are falling rapidly. The main causes of water

shortage in Dhaka are vital obstruction in

infiltration and excessive extraction of groundwater.

Rain is led away from cities and does not recharge

the groundwater, which is being mined extensively.

A research by Bangladesh Agricultural

Development Corporation (BADC) said that

Dhaka’s groundwater level had dropped to 52 meter

below mean sea level in 2011, compared with 46

meter in 2004 [1]. The main barrier for wider and

faster dissemination of suitable rain water

management system in Dhaka city is the lack of

knowledge, drainage facilities. Also, the lack of

facilities in gardening and cultivation prohibits the

use of rainwater. Due to excessive extraction of

groundwater to meet the demand of city dwellers

level of ground water in the

capital is depleting by 2 to 3 meters every year [2].

Hydrologists said dependence on groundwater

extracted from the city aquifers needs to be reduced

by providing alternative water supply, otherwise in

near future the city dwellers would face severe

water crisis [1]. The main purpose of this study is to

observe both causes and effects of waterlogging and

groundwater depletion and solution of those

problems by a low cost technology of artificial

infiltration system by wells. The model of artificial

infiltration well was installed in Dhaka University

of Engineering & Technology (DUET) campus. The

rest of this paper is organized as follows: Section 1

waterlogging problem, Section 2 groundwater

depletion, Section 3 materials and methods, Section

4 results and discussion and Section 5 concludes the

paper.




1. WATER LOGGING SITUATION IN DHAKA CITY

Dhaka city faces extensive water logging during the

monsoon (May to October) as a regular

phenomenon due to fast and uncontrolled

urbanization. This water logging is a problem

creating adverse social, physical, economic and

environmental impacts in the life and living in

Dhaka. Disruption of traffic movement and normal

life, damage of structures and infrastructure,

destruction of vegetation and aquatic habitats, loss

of income potentials are the prime effects of water

logging. Water logging in urban areas is an

inevitable problem for many cities in Asia. In

Bangladesh, Dhaka has serious problems related to

water logging. Daily activities in parts of the city

were nearly paralyzed and heavy traffic jams

occurred due to stagnant water on the streets. . The

authorities cannot implement effective system for

removing waterlogging in Dhaka city till 2015.

1.1 Profile of Water Logging In Dhaka City

In September 11th to 16th, 2004 heaviest ever

rainfall (341 mm) occurred in Dhaka City and its

devastating impact paralyzed the city life [3].

Following pictures (Figure 1) illustrates the water

logging situation due to the rainfall and its impacts

in Motijheel, the commercial hub of Dhaka City.

Fig. 1: Pictures illustrates the water logging

situation in Dhaka city, September 2004 [3].

Following picture (Figure 2) illustrates the water

logging situation due to the rainfall and its impacts

in Motijheel, the commercial hub of Dhaka City in

September 2015.

Fig. 2: Pictures illustrates the waterlogging

situation in Dhaka city, September 2015

1.2 Causes of Water Logging

The capital city of Bangladesh has become one of

the populous Mega City in the world, in recent

years facing extensive water logging during the

monsoon (May to October) as a common problem

of the city like water pollution, traffic congestion,

air and noise pollution, solid waste disposal, black

smoke etc.

The environment of Dhaka city is deteriorating

continuously day by day due to unplanned

urbanization, destruction of greeneries, increasing

in building area to meet the demand of migrated

people. As all the major economic activities are

centralized in Dhaka city, rural-urban migration is

naturally increasing at an alarming rate. The

covering areas in Dhaka city are increasing abruptly

by 210.37% from the year 1960-2014[4]. “Figure 3”

illustrates the present of covering area in Dhaka city

Built up areas Greeneries

Fig. 3: Topographic condition of Dhaka City in

2010 [5]

The main causes of waterlogging in Dhaka city is

"Total rainfall= Approximately Surface

Runoff/Flow” are as follows:




Fig. 4: Characteristics of Runoff in Urban Area

“Figure 4” illustrates the lower surface flow and

larger both interflow and base flow before

urbanization and also illustrates the inverse situation

after urbanization.

Infiltration (Interflow and Baseflow):

The covering areas in Dhaka city are increasing

abruptly by 210.37% from the year 1960-2014[4]

and also reducing water penetrable areas abruptly.

Almost all water penetrable areas are located in the

circumference of the city. Thus in the central area of

Dhaka city penetrable area is negligible where

water logging is occurring.

From this point of view, the amount and location of

infiltrated water cannot replenish the extracted

water in the densely populated area.

Evapotranspiration:

With the urbanization and changing life style the

construction areas in Dhaka city are increasing day

by day. The quantity of greeneries (0.13 acres for

1000 people) [6] in Dhaka city is inadequate, major

portion parts of this small amount of greeneries are

in the circumference of the city. Therefore,

transpiration loss will be negligible cause negligible

amount of greeneries in the central of Dhaka city.

This paper also postulates to omit evaporation loss

during rainfall which causes waterlogging as it is

time dependent and it requires minimum time for

drainage congestion from the rainfall event.

Therefore, the major portion of rainfall in Dhaka

city is converted into surface runoff/flow which

finally affect in water logging problem.

1.3 Effects of Water Logging

Urbanization disrupts natural drainage patterns,

natural watercourses are destroyed, natural retention

of runoff by plants and soil is removed and the

creation of impervious surfaces increases the

amount of runoff. This runoff becomes polluted as

solid waste, silt and contaminants are washed off

roads, leading to water logging and creating adverse

social, physical, economical as well as

environmental impacts.

(i) Social Problem

Disruption of Traffic Movement:

Disruption to traffic movement is an important

impact which arises during the water logging. It is

observed that normal traffic movement is hampered

during rainfall of over 25 mm [3] creating traffic

jam in the city area and people lose their valuable

time. Where the storm water cannot drain out,

puddles will form. This is not just inconvenient for

the pedestrians but also dangerous for road and road

users.

Fig. 5: Disruptions of Traffic Movement and

Normal Life

Disruption of Normal Life:

Water logging seriously disrupts normal life and it

has direct impacts on the poor, as they often live on

unsuitable, low-laying and flood prone or steep, and

unstable sites, have high-density housing, poor

urban planning and control and lack of investment

in urban infrastructure. The more affluent members

of society have the option to move to less flood

prone areas. But the poor bear the brunt of bad

drainage, through direct flood damage, pollution of

water supplies and the aquatic environment, the

breeding of vectors and soil erosion, leading to

direct financial costs, loss of income potential, as

the home may also be the workplace, and adverse

health impacts.




ii) Physical Problem

Damage of Infrastructure:

Water logging of the ground contributes to ground

heave, subsidence, dampness and other damage of

property. Water logging causes the damage to roads

during the rainy season leading to the movement

problem.

Fig. 6 Damage of Infrastructure

Damage of Structures:

The substructure of the buildings in the low laying

areas remains underwater due to water logging. The

brick foundations losses its longevity by being

affected with corrosive effect of salinity and

dampness is the after effect. In slums and low

income areas, most of the people live in temporary

and vulnerable buildings. These buildings become

badly damaged during the period of water logging.

Sometimes the occupants cannot use the buildings

and have to move to other areas, which create

psychological and economic stress for the poor

people.

iii) Environmental Impact

Water Pollution:

Theoretically, Dhaka WASA maintains two

separate sewer systems: one for domestic

wastewater and another for storm water. However,

in reality storm sewer also receive domestic

wastewater, which causes unwanted deterioration of

the storm water discharges. These discharges in turn

pollute the receiving water bodies including the

lakes, rivers and detention areas. Storm water

generated from the catchments areas carry

significant amount of pollutants. The level of

pollution in the storm water and in the receiving

water bodies is generally a matter of concern.

Increase of Water Born Diseases:

In urban areas, the most adverse impact of water

logging is the incidence and prevalence of various

diseases. In poorly drained areas, urban runoff

mixes with sewage from overflowing latrines and

sewers, causing pollution and a wide range of

problems associated with waterborne diseases.

Sometimes, the poor people have to rely on surface

or shallow groundwater sources that are polluted, as

they do not have access to portable water during the

period of monsoon. Malaria, respiratory problems,

eye and skin disease are also common in water

logged areas.

Damage of Vegetation and Reduce Aquatic

Habitats:

Water logging is the after effect of improper

drainage management. Stagnant water for a long

time and continuous release of wastewater damages

the trees and vegetation in and around the city areas.

Litter, sediment build-up and oil sheens on the

water surface are common visible effects of urban

pollution on surface water, which result in the

reduction in the numbers of aquatic plants and

animals. The increased flows resulted from

traditional drainage systems cause streams to scour

deeper and wider channels, adversely affecting

aquatic habitats. Eroded sediments are deposited

downstream in slower moving reaches of the river,

damaging aquatic habitats in these areas and

increasing sedimentation in wetlands.

iv) Economic Problem

Increase of Construction and Maintenance Cost:

Natural urban drainage system is decreasing day by

day due to uncontrolled rapid urbanization and

water logging is the ultimate effect of not only the

physical, social and environmental problem, it is an

economic burden as well. Water logging increases

the construction and maintenance cost because it

reduces the life span and damage to roads and

metalloid pipes of various underground utility

services such as water, telephone, sewerage etc. It

needs a huge cost to replace these facilities and

increases the maintenance cost.

Shortage of Water:

Water logging due to the increase of impermeable

urban areas also leads to a lowering of the ground

water table under a construction site. This has not

only environmental impact but also economic

impacts, as it contributes to water shortage, and may

cause soil subsidence and consolidation problems.

Loss of Income Potential:

Sometimes, water enters into houses and the floor

and wall remains wetted for a long period and it




damages the household goods, stored food grains

etc. The effects of water logging also leads to direct

financial costs, loss of income potential, as the poor

people may use their home for workplace. Water

logging hampers traffic movements; therefore,

creates an obstacle for communication and timely

supply of goods, which means the loss of time,

reduced production and economic losses.

Fig. 7 Hamper the Income Potential.

2 GROUNDWATER DEPLETION OF DHAKA CITY

In Dhaka city, groundwater extraction started from

a depth of 100 meters and in some extreme

condition the well goes up to 300 meters to reach

the main aquifer. The depletion rate varies from

area to area as in Mirpur the groundwater level

dropped 53.75 meters between 1991 and 2008 at a

rate of 3.2 meter per year. While the decline was 1.1

m/y in Mohammadpur, 2.2 m/y in Sabujbagh, 0.5

m/y in Sutrapur, and 0.8 m/y in Dhaka Cantonment

during the same period [7]. The city’s groundwater

level has dropped about 20 meters over the last

seven years at a rate of 2.81 meter per year, and

from the year 2000, the rate is increasingly high [7].

A circumstantial overview on groundwater

depletion of Dhaka City has been given by A.F.M

Azim Uddin and Mohammed Abdul Baten (2011).

“Figure 8” illustrates the groundwater depletion up

to 2050 and it predicts that the groundwater table

will be lowering down to 120 meters by 2050 from

the existing water table. This depletion will hamper

the constant water supply as many of the operating

deep wells may shut down due to water

unavailability. The production cost may rise at the

highest peak.

Fig. 8: Groundwater Depletion Trend of Dhaka

City [7]

2.1 Causes of Groundwater Depletion

Ground water depletion in Dhaka city is promoting

by two key reasons.

(i) Vital obstruction in infiltration.

(ii) Excessive extraction of ground water.

(i) Vital obstruction in infiltration

The environment of Dhaka city is deteriorating

continuously day by day due to unplanned

urbanization, destruction of greeneries, increasing

in building area to meet the demand of migrated

people. As all the major economic activities are

centralized in Dhaka city, rural-urban migration is

naturally increasing at an alarming rate.

World Health Organization (WHO) recommends

4.23 acres of greeneries per 1000 people. In

contrary, the Development Area Plan (DAP) in

Dhaka has proposed an insufficient quantity of

greeneries (0.13 acres for 1000 people) [6]. The

covering areas in Dhaka city are increasing abruptly

by 210.37% from the year 1960-2014 [4]. “Figure

9” shows decreasing rate of green spaces and water

bodies, and increasing covering area and also

declining groundwater level with increasing built-

up areas or covering areas in Dhaka city.




Fig. 9: (x) Decreasing rate of green Spaces in

Dhaka City (Islam et al., 2013)[5] and (y)

Declining groundwater level with increasing

built-up area in Dhaka city [1]

Such built-up area provides vital obstruction in

infiltration, which finally affects the groundwater

table. In 1989, the built-up areas in Dhaka city were

much less than green spaces and water bodies, in

that year the groundwater table was less than 20m.

In 2010 the built-up areas in Dhaka city were much

higher than green spaces and water bodies, in that

year the groundwater table below was 69m and [1].

Therefore the groundwater depletion within 21

years (1989-2010) is 49m.

(i) Excessive extraction of ground water

Dhaka is now the 7th largest city in the world and

by 2020 it will be the 2nd largest city in the world.

Present population of Dhaka City is about 12

million and projected population by 2025 is about

22 million.

Fig. 10: Showing increasing rate of Dhaka and

Kolkata.

Urban Areas Population 1950- 2010 and with

projected to 2025.

This unexpected increasing in population is

increasing the demand of groundwater.

2.2 Potential Groundwater Recharge in Dhaka

City

Assessment of future groundwater development

potential is a prerequisite for the proper and

sustainable use of the resource. Terribly polluted

surface water resources and increased urbanization

exacerbate the depletion rate of groundwater in

Dhaka city Groundwater availability for pumping in

terms of potential recharge estimated by simple

hydrological balance as follows:

……………………… (i)

Where,

Re = Potential Recharge

R = Rainfall

Pe = Potential Evapotranspiration

S = Surface Run-off

Average Annual Rainfall of Dhaka city is about

2,100mm [8]. Potential recharge is the excess of

rainfall over run-off and potential

evapotranspiration. To make the estimation more

comprehensive, monthly basis is preferred over

seasonal basis. Surface run-off estimated as a

percentage of rainfall (20-50 percent) depending on

the amount and intensity of rainfall, topography or

land use pattern, and geo-hydrological condition. As

an urbanized area with much paved structures, the

surface run-off for Dhaka city has been estimated as

50 percent. Evaporation is the primary process of

water transfer in the hydrological cycle. The

evaporation including transpiration form vegetated

surface is known as potential evapotranspiration. To

calculate the potential recharge rate, potential

evapotranspiration (Pe) should be taken into

consideration. To calculate Pe, the “Blaney-

Criddle” formula has been used in the current

study:

……………………… (ii)

Where, Pe = Potential evapotranspiration

P = Mean daily percentage of annual

daytime hours

T = Mean daily temperature

The mean temperature for Dhaka city has been

estimated through averaging monthly maximum and

minimum temperature and the mean temperature

was 26.06˚C. To determine the value of p (Mean

daily percentage of daytime), the value of latitude is

necessary. Dhaka city’s latitude 230 N, p has been

estimated as 0.27.




=0.27(0.46×26.06+8)

= 5.40 mm/day

Where, p= 0.27%

T=26.06˚C

Putting the value of Pe into the equation (i),

= 2100-5.40-1050

= 1,044.6 mm/year

= 1.0446 m/year

≈ 1.045 m/year

Where, P= 2100 mm/year

Pe= 5.40 mm/day

S= 1050 mm/year

The finding shows that potential groundwater

recharge for Dhaka city is 1.045 m/y while the

groundwater depletion rate is 2.81 meter per year.

Therefore, despite sufficient amount of rainfall

Dhaka city experiences 1.765 m/y groundwater

recharge deficit every year. Increasing rate of

urbanization and decreasing surface water bodies

will worsen the situation.

2.3 Consequences of Ground Water Depletion

(i) Lowering of the Water Table

Fig. 10: Groundwater crisis in Dhaka city [1]

The most severe consequence of excessive

groundwater pumping is lowering down the

groundwater table. If groundwater levels decline too

far, then the well owner might have to deepen the

well, drill a new well, or at least attempt to lower

the pump. In addition, as water levels decline, the

rate of water yield may decline.

Following picture (Figure 10) illustrates the

procession for groundwater by the dwellers of

Dhaka city. Hydrologist said dependence on ground

water extracted from the city aquifers need to be

reduced by providing alternative source of water

supply otherwise in near future the city dwellers

would face severe water crisis.

(ii) Increased Costs

Water production cost increases with decreasing

groundwater level. Water must be lifted higher to

reach the land surface than before if the water level

go down. If pumps are used to lift the water, more

energy will be required to drive the pump that

would eventually increase the expense of the users.

(iii) Reduction of Water Flow in Streams and

Lakes

A great deal of the water flowing in rivers comes

from seepage of groundwater into the streambed.

However, groundwater pumping can alter water

circulation between an aquifer and a stream, lake, or

wetland by either intercepting groundwater flow

that is discharged into the surface-water body under

natural conditions or by increasing the rate of water

movement from the surface-water body into an

aquifer. A related effect of groundwater pumping is

the lowering of groundwater levels below the depth

which is required by the streamside or wetland

vegetation to survive. The overall effect is a loss of

riparian vegetation and wildlife habitat.

(iv) Land subsidence

The basic cause of land subsidence is the loss of

support below ground. Indiscriminate groundwater

extraction from main aquifer may contribute to land

subsidence.

(v) Deterioration of water quality

The rise in sea level is about 7.5mm per year and

depletion in groundwater table is about 2to3m per

year. Under natural conditions, the boundary

between the freshwater and saltwater tends to be

relatively stable. Over pumping can cause saltwater

to migrate inland and upward, resulting in saltwater

contamination of the water supply.

Fig. 11 Impact of over pumping of groundwater

[7].




2.4 Current Groundwater Saving System in

Dhaka City

DWASA has committed to reduce dependency on

ground water from 87% to 50% by 2015 and in this

respect [9]. DWASA needs implementation of its

projects as planned and discussed in the dialogues.

An inclusive and well planned coordination body

has planned to be formed involving all related

Ministries to solve water problems in Dhaka city.

At present, 45 DTWs in deeper aquifer are in

operation and another 50 DTWs have been planned

to install. Towards water security in Dhaka city, A

Dialogue on “Surface water the most potential

future alternative for water supply in Dhaka City”

held on 19th July, 2009 organized jointly organized

by Bangladesh Water Partnership (BWP), Dhaka

Water Supply and Sewerage Authority (DWASA)

and Policy Supply Unit (PSU), Local Government

Division, Ministry of Local Government, Rural

Development and Cooperatives [10].

Outcomes of the Dialogue/Recommendations:

Installation of CETPs (Common Effluent

Treatment Plants) at identified locations in Tongi,

Tarabo and Gazipur industrial Clusters

Medium and large industries are persuaded to

install ETPs; small industries shifted to industrial

clusters and provided with common effluent

treatment plants.

All industries adopt cleaner production

technologies to reduce generation of pollutants

The river bottoms are to be dredged to remove

polluted soil and sludge. The problem of disposal of

sludge and soil is critical and should be addressed.

Rainwater is used to artificially recharge

groundwater

Reservoirs are constructed at Ashulia to store

water for the critical months of March-May.

The authorities cannot install any effective system

for saving groundwater in Dhaka city till 2015.

3. MATERIALS AND METHODS

The rainwater management potential of Dhaka City,

with an area of 1580 sq. km, assuming a coefficient

of 50%, and the average annual rainfall of 2000.0

mm (approximately) is 158.0 million liters or 41.74

million gallons [2]. In Dhaka city there is 50% roof

area of total area. A proper management system has

a great opportunity to reduce water logging in the

roads and environmental pollution by reducing

surface runoff in large scale. In this process the

rainwater intercepted in the building will be passed

into the unconfined aquifer by gravity action

through the wells. Because of high downward water

pressure and permeability of aquifer in this system,

water will infiltrate in the aquifer significantly, and

will enrich ground water storage.

3.1 Components of the Artificial Infiltration Well

Direct recharge or wells (Fig. 3.1) are used where

permeable soils and/or sufficient land area for

surface infiltration are not available, vadose zones

are not suitable for trenches or wells, and aquifers

are deep and/or confined. Truly confined aquifers

might still be rechargeable, because such aquifers

accept and yield water by expansion and

compression of the aquifer itself and, particularly,

of inter bedded clay layers and aquitards that are

more compressible than the sands and gravels or

consolidated materials of the aquifer.

Therefore, the components of proposed artificial

infiltration system from (Figure 12) are as follows:

Well pipe: It passes rain water to the first aquifer

where permeability is high after passing hard layer

in which permeability is low.

Screening: Due to high gravity action and

permeability of soil mass the rainwater will

infiltrate quickly through screening system.

B-pipe: when the rainfall intensity is very high,

then it discharges extra rain water from roof for

providing structural safety from heavy load on roof

of rainwater.

Filtration: The rainwater of the building roof is

almost free from impurities for being reinforcement

concrete roof. In our study the filter media was also

used for sustainability of the system. The filter

media are very efficiency in retaining finer and

colloidal particles. For removing waterlogging in

the roof which provides additional surcharge load

on the structure, the filter media will be with

sufficient infiltration rate.

3.2 Design of Wells

The design elements of artificial recharge system by

wells are in (fig. 3.1). The design processes meet

with a common artificial recharge well.

Design of the well pipe:

Area of the well pipe; A=Discharge/Velocity

[Permissible Velocity 2m/s to 3m/s]

Diameter of the Pipe ]




Fig. 12: Artificial infiltration well

Design of the strainer:

The diameter of the strainer and well pipe will be

uniform

Therefore, the seepage velocity of soil (Vs)

[Darcy’s Law]

Where,

K= Permeability of soil.

Hydraulic gradient

The value of pressure head H depends on the height

of building, friction loss and required rising in

groundwater table.

L=Seepage length.

Strainer Length:

3.3 Model Test for Artificial Infiltration

The following materials and arrangement have been

chosen for the model of artificial infiltration. The

model was installed in nearest Dr. F R Khan Hall of

DUET campus.

Materials:

PVC pipe of 1.5 inch diameter and 120feet depth

from ground level was used as vertical well pipe.

Screening pipe of 1.5 inch diameter and 10 feet

length was used at the bottom of vertical pipe for

infiltrating water.

Stone was used surrounding the screening pipe

for removing the clogging problem of filter by clay

formation.

Bore hole:

About 3 inch diameter bore hole was dug by wash

boring method against 1.5 inch well pipe.

Fig. 13: Showing soil excavation for bore hole

Fig. 14: Showing well pipe installation in the

bore hole




Fig. 15: Showing stone packing around the

screening pipe

Fig. 16: Showing washing of bore hole for

removing clay

Sample collection:

Soil (sample) was collected for permeability test

All samples were collected from the layer where

screening pipe was placed.

Well installation:

Before installation the well, the bore hole was

washed properly for removing clay formation

problem at the bottom and also surrounding of the

screening pipe. After joining the screening pipe

with PVC pipe, the pipe were placed together in

bore hole. The surrounding of the screening pipe

was packed properly by stone and upper portion

was filled by sand.

4. RESULTS AND DISCUSSIONS

Artificial infiltration of roof rainwater by well is a

new idea which may be effective in removing water

related crisis of Dhaka city. Any study was not done

on artificial infiltration of roof rainwater by well. In

the face of growing demand for groundwater in the

city, the authority has no alternative but to look for

a permanent solution of enhancing the capacity of

recharging the rainwater into underground water

table. From this point of view, a new idea has been

highlighted by this study for removing water related

crisis. Therefore, this study has no ability to

postulate that model performance results were best

but more attention and precaution were followed

during study period

4.1 Model Performance

Performance of models of artificial infiltration well

was evaluated by both actual and theoretical

groundwater storage capacities of wells are as

follows:

(i) Actual Groundwater Storage Capacity (Qac):

Fig. 17: Showing water measurement drum,

water supply pipe from building roof and water

entering in well pipe respectively

A sample calculation for groundwater storage

capacity is presented in the Table 1 for three

experiments.

Table 1

Actual groundwater storage capacity from

model test

Experiment

No.

Pressure

Head

H

(Meter)

Volume of

infiltrated

water

V (m3)

Time

T

(min)

Actual

Storage

Qac=

(V/T)

(m3/min)

1

51.829

0.05470

5

0.01095

2 47.71 0.05115 5 0.01023

3 44.51 0.04485 5 0.00897

The pressure head (H) was measured from center of

the screening pipe to the center of water

supply/measurement drum. The water was supplied

using measurement drum from different floor level

and roof of Dr. F R Khan Hall




(ii) Theoretical Groundwater Storage (Qth):

The theoretical groundwater storage discharge was

calculated based on Darcy’s formula

Permeability of soil (K):

The permeability of the soil was determined in

DUET soil test laboratory by the author’s. The test

was conducted for constant head method.

Fig. 18: Showing permeability test in DUET Soil

Lab

Table 2

Permeability of soil sample

Sample

No.

Permeability

K (m/min)

Average

Permeability

K (m/min)

1 0.083

0.088 2 0.094

3 0.087

A sample calculation for theoretical groundwater

storage capacity is presented in the Table 3 for three

Experiments.

Table 3

Theoretical groundwater storage capacity from

model

Expt.

No.

Permeability

K (m/min)

Surface

Area of

screening

pipe

As (m2)

Hydraulic

Gradient

i= H/L

Theoretical

Storage

Qth(m3/min)

1

0.088

0.0035 51.829 0.0159

2 0.0035 47.71 0.0145

3 0.0035 44.51 0.0137

Seepage length L was assumed to be unity for being

uncontrolled and immeasurable seepage length in

aquifer.

(iii) Storage Coefficient (Cd):

Storage coefficient is determined from actual and

theoretical discharge. Storage coefficient for three

models are in calculated in the Table 4.

Table 4

Storage coefficient (cd)

Expt.

No.

Actual

Storage

Qac

(m3/mi

n)

Theoretica

l Storage

Qth

(m3/min)

Storage

Coefficient

Average

Cd

1 0.01095 0.0159 0.702

0.687

2 0.01023 0.0145 0.705

3 0.00897 0.0137 0.654

Suggested Formula: The Artificial groundwater

storage discharge:

Where,

Cd = Storage Coefficient (Proposed value 0.687)

K= Permeability of soil.

H = Pressure Head.

L = Seepage length is assumed to be unity. [We

have chosen unity for being infinite seepage length

surrounding the screening pipe]

As = Surface area of Screening pipe.

4.2 Expected Results Regarding Dhaka City

The following results will be satisfied if proposed

artificial infiltration well is installed in Dhaka City.

Groundwater storage: A sample calculation for

groundwater storage is presented in the Table 5.

Taking 10% losses; therefore net average rainfall

will be 1890 (0.9*2100) mm/year.

Table 5

Calculation of groundwater storage from roof

rainwater

Roof

Area

A(km2)

Net

Average

Rainfall

mm/year

Storage in aquifer million

liters per year from

rainwater

200

1890

378000

250

1890

472500




Therefore, because of the utilization of rainwater

into the groundwater storage, environmental impact

from these will also be minimized in the area, as

these will not be accumulated in surface as before.

The rise in sea level is about 7.5mm per year and

depletion in groundwater table is about 2to3m per

year. Therefore, this proposed artificial infiltration

system will be helpful in saving the groundwater

from salinity impact in future life.

The void in soil strata is max in Dhaka city which

provides stable support for high density building

structure due to deep depletion of groundwater

table. When dangerous earthquake will occur in

Dhaka city, Dhaka may goes for deep depression

due to combine action of earth shake and excessive

surcharge weight on soil strata from building

structure. Therefore, this proposed artificial

infiltration system will also be helpful in saving the

city from such disaster by filling the void in soil

mass with infiltrated water.

Groundwater pollution as like Arsenic pollution

of Dhaka city will be reduced by diluting the

concentration of pollution.

The rain water will infiltrate continuously during

rainfall by gravity action (Pressure head).

Therefore, extra energy will not be required.

5. CONCLUSIONS

ANDRECOMMENDATIONS

The devastating impact of the downpours that

paralyze Dhaka is a salutary reminder of the

severity of problems, and the necessity for the

government to take corrective measures on a

priority basis In the face of growing demand for

water in the city, the authority has no alternative but

to look for a permanent solution of enhancing the

capacity of recharging the rainwater into

underground water table. The major conclusions

may be summarized as follows:

The model has shown good result in groundwater

storage. The actual ground water storage was

0.01095m3/min at 170 feet pressure head with

1.5inch diameter and 10 feet length screening pipe.

The theoretical groundwater storage was

0.0159m3/min at 170 feet pressure head and

0.088m/min permeability with 1.5inch diameter and

10 feet length screening pipe.

The artificial groundwater storage discharge:

where, storage

coefficient Cd is 0.687.

The variation in actual and theoretical storage

capacity with increasing pressure head has shown

linear variation.

The groundwater storage rate is dependent on

permeability of soil and pressure head. The

screening pipe should be placed below the ground

where permeability of soil mass is comparatively

more.

It is hoped that this study has highlighted a idea

“Artificial Infiltration of Roof Rainwater” for that

are also being discussed in the policy and

professional domains for quite some time from

desperation of finding out a way for solving

groundwater depletion and waterlogging problems

in Dhaka City.

Recommendations for further study:

In this study, the value of L was considered unity

for being infinite seepage length surrounding the

screening pipe in determining hydraulic gradient [i=

(H÷L)]. Further study should be required for

determining seepage length.

All models were prepared with same diameter

pipes for funding limitation. For most effective

result, further study should be done on models

which will be prepared with different diameter

pipes.

All models were installed in DUET campus for

funding limitation. For most effective result, further

study should be done on models which will be

installed in different places of Dhaka City.

ACKNOWLEDGMENT

We would like to thank the Almighty Allah for

helping me in making this report a reality.

The authors wish to express their deepest gratitude

and special thanks to their Supervisor Professor Dr.

Md. Akramul Alam, Civil Engineering Department,

DUET, for his constant support, incessantable

guidance, spirited encouragement, constructive

criticism, valuable comments and suggestions at

every stage of this study.

We would like to express our sincere thanks to

Professor Dr. Mohammed Alauddin, Civil

Engineering Department, DUET, for his kind

motivation, encouragement and advice.

The support of the laboratory staff of the




Department of Civil Engineering during the course

of the research work is gratefully acknowledged.

The authors also expresses their sincere thanks to all

laboratory staff of Environmental Engineering and

soil engineering Laboratories for their assistance

and support during the course of this research work.

The authors gratefully acknowledge the financial

support received during this work from DUET,

Gazipur. The authors also acknowledge the moral

support and suggestions from the faculty members

of DUET. The authors are also grateful to his family

members, colleagues and friends for their co-

operation and companionship extended to him

during this study.

REFERENCES

[1] Sushmita Sengupta, Amandeep Kang, Nitya Jacob,

September 2012, A Briefing Paper on the State of

Groundwater Management in Bangladesh.

[2] Sumon, F. R., A. K. M Kalam, A., April 27-2014.

Rainwater Harvesting and the Scope of Enhancing

Ground Water Table in Dhaka City. Bangladesh

Institute of Planners Journal.

[3] Tawhid, K.G. 2004. “Causes and Effects of Water

Logging in Dhaka City, Bangladesh”, TRITA-LWR

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[4] Uddin, M.N., Anwar, M. F., Rahman M.T., Mobin,

and M.N. 2014. An Investigation on the Pattern of

Land Use Change In Dhaka City Using Remote

Sensing and GIS Application. Journal of

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[7] A.F.M Azim Uddin and Mohammed Abdul Baten,

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[9] Dhaka Water Supply and Sewerage Authority

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