Assessing the Potential of Tambakboyo Retention Basin for Raw Water

Supply in the City of Yogyakarta Indonesia

Edy Sriyono

, Agung Purwanto

, Sardi

, Nindyo Cahyo Kresnanto

, Tania Edna Bhakty

and

Muhammad Kunta Biddinika

Civil Engineering Master’s Degree Program, Janabadra University, Jalan Tentara Rakyat Mataram 55-57 Yogyakarta,

Keywords:

Water resources, retention basin, water potential.

Abstract:

This paper presents an assessment of the potential of Tambakboyo basin as one of the potential new water

sources due to the water shortage in some areas of the city of Yogyakarta. It is a retention basin located in the

Sleman Regency, Special Province of Yogyakarta, Indonesia. The basin has overﬂow elevation of +147,00 m

and retrieval pipe elevation of +141,00 m. This assessment includes an analysis of the inﬂow, rain fall on the

surface of the reservoir, outﬂow for water requirements, water loss from evaporation and seepage. By using

the scales of water balance and simulation of water retrieval, we are able to determine water potential of the

basin for clean water.

1 INTRODUCTION

Some areas in Yogyakarta City have experienced wa-

ter crisis. The region consists of 5 (ﬁve) subdis-

tricts, namely District Gondokusuman, Mergangsan,

Mantrijeron, Jetis and Umbulharjo. To overcome the

problem, water sources that can be utilized for water

daily usage should be reduced.

The increasing demand for water causes some

areas in Yogyakarta to experience water shortages.

These short comings can be met by utilizing the po-

tential of existing water resources. In Kabupaten Sle-

man there is a potential source of water that is likely

to be used to meet water shortages. The source is Em-

bung Tambakboyo which until now has not been uti-

lized up to its potential. In addition to the overﬂow,

the embung location is also higher than areas that re-

quire water, making it possible to stream the water

using gravity.

Embung Tambakboyo is one of water retention

basin that was built from 2003 until 2008 in Tambak-

boyo River upstream or in the meeting between Klan-

duan River and the downstream of Sembung River.

The embung location is in Condongcatur Village, De-

pok District, Sleman Regency, Special Region of Yo-

gyakarta. According to the interviews with local resi-

dents around the embung, in the dry season Tambak-

boyo Embung pond is always fully charged and water

always overﬂowed through the spillway. The condi-

tion gives an illustration that Embung Tambakboyo

has water potential that can be utilized for raw water

usage (Pengairan, 1986) (Kamiana, 2011).

For that we need a study of how much potential

water Embung Tambakboyo can be utilized to meet

the lack of water in the city of Yogyakarta. The study

will be conducted by simulating water retrieval based

on the water balance of embung which is the relation-

ship between inﬂow, outﬂow and the number of con-

tainers (Gustian, 2014).

2 LITERATURE REVIEW

2.1 Water Resources Development

According to (Triatmodjo and Terapan, 2008), water

resources development can be grouped into two activ-

ities, namely water utilization and water management

(Figure 1). Water utilization activities include the pro-

vision of water for irrigation water needs,households,

ofﬁces, hospitals, education, houses of worship, ho-

tels, river maintenance/raiding, ﬁsheries, livestock,

industry and so on. These various needs can be served

by available water which can be either surface water

or ground water with certain reliability. Water reg-

ulation activities include ﬂood control, drainage and

waste management. These activities are conducted to

Sriyono, E., Purwanto, A., Sardi, ., Kresnanto, N., Bhakty, T. and Biddinika, M.

Assessing the Potential of Tambakboyo Retention Basin for RawWater Supply in the City of Yogyakarta Indonesia.

DOI: 10.5220/0009878900960100

In Proceedings of the 2nd International Conference on Applied Science, Engineering and Social Sciences (ICASESS 2019), pages 96-100

ISBN: 978-989-758-452-7

overcome the existence of excessive water in the form

of ﬂoods that can cause harm to the community.

Figure 1: Water Resources Development Activities.

The relationship between the two activities is in

the rainy season the water will be abundant so that

should be thrown into the sea so as not to cause

ﬂood. But in the dry season the availability of wa-

ter is signiﬁcantly reduced, making itdifﬁcult to meet

the needs of water that is relatively ﬁxed and even in-

creases along with the increase of population. To that

end, it takes facilities such as embung to accommo-

date excess water in the rainy season and use it in the

dry season.

Water utilization includes the study of water avail-

ability and water requirements as well as planning fa-

cilities/buildings that can meet these needs from avail-

able water availability. For that we need to know the

amount of water available and the current water needs

and predictions of future needs. From both analy-

sis, we can calculate water balance in a watershed,

by comparing the availability and the need for water.

2.2 Water Balance

Embung is a water retention structure that serves to

store water while at the time of excess water and

released in the event of water shortage. The wa-

ter balance of the embung is based on the continu-

ity equation which is the relationship between in-

let water, outlet water and the number of contain-

ers. Figure 2 shows the water balance in the embung,

which can be mathematically expressed in terms of

the following equation (Asdak, 2018), (Brotowiry-

atmo, 1993)(Hadisusanto, 2010):

Q + P = O + E + I + ∆S (1)

where Q is inlow from the river, rainfall that falls

on the surface of the reservoir, O is outﬂow for irri-

gation water needs; raw water and so on, E is evapo-

rated, I is water loss from seepage, and ∆S is the water

reservoir in the reservoir.

Figure 2: Embung’s water balance.

3 METHODOLOGY

3.1 Location

The research was conducted at Embung Tambakboyo

in Tambak Bayan River, Condongcatur Village, De-

pok District, Sleman Regency, Yogyakarta Special

Region as presented in Figure 3.

Figure 3: The location of Embung Tambakboyo.

3.2 Inﬂow

The inﬂow water discharges consists of the ﬂow of

streams and rain falling on the surface of the embung.

River ﬂow discharge in question is the result of Mock

simulation that has been calibrated with debit data .

While the rain falling on the surface of the embung

multiplied by the surface area of the embung.

3.3 Outﬂow

The outﬂow water discharges consist of water require-

ments for various purposes (water requirements for

irrigation and ﬁsheries), and water loss from evapora-

tion and seepage.

Assessing the Potential of Tambakboyo Retention Basin for RawWater Supply in the City of Yogyakarta Indonesia

3.4 Water Balance Simulation of Water

Retrieval

The availability of Tambakboyo water pond comes

from the inﬂow and outﬂow. Analysis of water avail-

ability is estimated based on the water balance of the

reservoir calculated using equation (1), then the simu-

lation of water harvesting was conducted to determine

the maximum limit of water retention ponds.

4 RESULT AND DISCUSSION

4.1 Inﬂow

The inﬂow of Embung Tambakboyo consists of 90%

(Q90) mainstay discharge of Mock simulation result

and 90% rainfall (R90) result of area rainfall analy-

sis multiplied by embung pond area of 60,542.4 m2

as presented in Figure 4. The table shows that the

largest inﬂow was in February, which was 1989.29

lt/sec while the smallest inﬂow was in December,

which was 36.12 lt/sec.

Figure 4: Inﬂow (Q + P).

4.2 Water Loss due to Evaporation

Water loss due to evaporation above the water sur-

face of the embung is calculated from the evapora-

tion value of modiﬁed Penman method multiplied by

the surface area of the pond. In full conditions, the

water level elevation is at + 147.00 m elevation with

a surface area of 60,542.4 m2. The results of Em-

bung Tambakboyo evaporation calculations are pre-

sented in Figure 5.

The table shows that the largest water loss due

to evaporation was in October, which was 3.37 lt/sec

while the smallest water loss due to evaporation was

in July, which was 2.49 lt/sec.

Figure 5: The evaporation of Embung Tambakboyo.

4.3 Water Loss from Seepage (I)

The ﬂow-net projection (Hardiyatmo, 2012), result-

ing in 8 (eight) ﬂow lines (Nf) and 30 (thirty) equipo-

tential lines (Nd). If the water level is at + 147.00

m elevation, there is a high energy difference (h) be-

tween the beginning and end (9,89 m) equipotential

energy line (Nd). From the depiction presented in

Figure 6, water loss from seepage that occurred in

Embung Tambakboyo is 0.073 lt/sec, the full calcu-

lation is presented in Figure 7. The table shows that

the largest water loss from seepage (I) is at + 147.00

m elevation, which was 0.075 lt/sec while the smallest

water loss from seepage (I) is at + 141.00 m elevation,

which was 0.028 lt/sec.

Figure 6: Flownet of Embung Tambakboyo.

Figure 7: Calculating the seepage of Embung Tambakboyo.

4.4 Water Balance and Simulation of

Water Retrieval

The water scale of Embung Tambakboyo Watershed

is the ratio between the inﬂow and the outﬂow. The

difference from the comparison provides information

ICASESS 2019 - International Conference on Applied Science, Engineering and Social Science

on water availability from January to December. In

the case of a water surplus (+) or water deﬁcit (-

), the pond retention pond remains fully charged at

387,947.47 m3 at +147.00 m elevation. The water

balance of the Tambakboyo Embung Watershed is

presented in Figure 8.

Figure 8: Water balance of Embung Tambakboyo.

In the case of surplus water (excess water), the ful-

ﬁllment of water needs for various purposes (outﬂow)

using the inﬂow of water (inﬂow). If there is still any

residual from the inﬂow, the water is considered to be

melted.

In the state of water deﬁcit (lack of water), the ful-

ﬁllment of water needs for various purposes (outﬂow)

using water reservoir embung. This situation resulted

in decreasing embung volume and decreasing of sur-

face water level. Change of embung water storage is

calculated based on water balance of embung.

In Embung Tambakboyo at the rear of the drain

door, there is a 16-inch galvanized tube at + 141.00 m

elevation. The pipe is ﬁtted with the purpose can be

utilized if there is a plan of utilization of Tambakboyo

water pond for raw water.

Based on the water balance of the embung, the

volume of the containment and the presence of the

pipe, a simulation of water harvesting to determine

the maximum limit of water retention ponds from el-

evation +147,00 m to elevation + 141,00 m. The sim-

ulation uses alternate picking, 10 lt/sec, 20 lt/sec, 30

lt/sec, 40 lt/sec, 45 lt/sec and 48 lt/sec. The calcula-

tion of the complete water-taking simulation is pre-

sented in Figure 9.

Figure 9: Graphical simulations of water retrieval at Em-

bung Tambakboyo.

Figure 9 provides information on the inﬂuence of

each of the water-taking alternatives. The information

will be explained as follows:

1. Take water of discharge 0 lt/sec The utilization of

the catchment water occurred in December when

Embung Tambakboyo was ina state of water de-

viation. When uses 0 liters/second of water re-

trieval, leaving a volume of 385,928.30 m3 of

contained water at an elevation of + 146.97 m.

2. Take water of discharge 10 lt/sec The utilization

of shelter water occurs from November to Decem-

ber at the time of Embung Tambakboyo in a state

of water deviation. When a 10 liters/second water

discharge is used, it will leave the volume of wa-

ter in the reservoir 352,676.69 m3 at elevation +

146.41 m.

3. Take water of discharge 20 lt/sec The utilization

of shelter water occurs from October to December

when Embung Tambakboyo is in a state of water

deviation. When a 20 liters/second liquefaction

discharge is used, it will leave a water volume in

the reservoir of 278,698.03 m3 at an elevation of

+ 145.15 m.

4. Take water of discharge 30 lt/sec The utilization

of shelter water occurs from October to December

when Embung Tambakboyo is in a state of water

devisit. When a 30 liters/second water discharge

is used, the volume of water in the container will

be 199.210.03 m3 at elevation + 143,74 m.

5. Take water of discharge 40 lt/sec The utilization

of shelter water occurs from October to Decem-

ber when Embung Tambakboyo is in a state of

water deviation. When a 40 liters/second water

discharge is used, it will leave a water volume in

container of 119.722.03 m3 at elevation + 142.31

6. Take water of discharge 45 lt/sec The utilization

of shelter water occurs from October to Decem-

ber when Embung Tambakboyo is in a state of

water deviation. When a 45 lt/sec water discharge

is used, it will leave a volume of 79,978.03 m3 of

water in storage at + 141.54 m elevation.

7. Take water of discharge 48 lt/sec The utilization

of shelter water occurs from October to December

when Embung Tambakboyo is in a state of water

deviation. When a water harvesting rate of 48 lt/dt

is used, it will leave a volume of water in the reser-

voir of 56,131.63 m3 at elevation + 141.09 m.

5 CONCLUSIONS

1. Embung Tambakboyo is a very strategic water

source that can be used to help overcome the lack

of water in some areas in Yogyakarta city. This is

because the location is higher than the area in the

city of Yogyakarta that requires the water.

Assessing the Potential of Tambakboyo Retention Basin for RawWater Supply in the City of Yogyakarta Indonesia

2. By utilizing the volume of the embung em-

bankment to reach the dead storage elevation

(+141.00), then dry season with 90% reliability,

the water in Tambakboyo embung can be col-

lected by 48 lt/sec without disrupting the utiliza-

tion of exsisting water, such as for Irrigation and

ﬁsh ponds.

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