Civil Engineering Forum Volume XXII/2 – May 2013

1365

ANALYSIS OF HYDRAULIC FLOOD CONTROL STRUCTURE AT PUTAT BORO RIVER

Ruhban Ruzziyatno
Directorate General of Water Resources, Ministry of Public Works, Republic of Indonesia

Email: [email protected]

ABSTRACT

Putat Boro River is one of the main drainage systems of Surakarta city which drains into Bengawan Solo river. The primary
problem when flood occur is the higher water level of Bengawan Solo than Boro River and then backwater occur and

inundates Putat Boro River.

The objective of the study is to obtain operational method of Putat Boro River floodgate to control both inflows and outflows

not only during flood but also normal condition. It also aims to know the Putat Boro rivers floodgate operational function to

reduce inundation. Putat Boro river water level variation and Bengawan Solo river water level variation were used for

simulation of Boro river floodgate routing. The simulation used 10-year inflows, 50-year inflows, and 100-year inflows return

period and Boro water level variation are +82.50 m, +83.00 m and +84.00 m.
The results of the study show that the effective opening of floodgate are 0.35 m – 0.55 m for +82.05 m of Bengawan Solo

water level, 0.50 m – 0.65 m for +82.55 m of Bengawan Solo water level and 0.70 m – 0.85 m for +83.48 m of Bengawan Solo

water level, for reducing water level of Boro river flooding.

Keywords: Flood, drainage systems, floodgate and flow routing.

1 INTRODUCTION

Flood that occurs periodically in dense populated area,

particularly in urban area has caused damages and

losses to physical structures, even loss of human lives.

Flood in 1966 inundated almost 2/3 of Surakarta city

including urban area. Inundation attained 1 m up to 2

m depth and caused 90 people died.

Boro River is one of many drainage canals flowing

into Bengawan Solo River. Its catchment comprises

Sewu, Pucang Sawit, Jagalan, Purwodiningratan, and

Tegalharjo sub district, Jebres district, Surakarta city.

Flood that occurs almost every year is affected by

backwater phenomena. It occurs when water level of

Bengawan Solo River is higher than ground level of

catchment of Boro River. The flood control of Putat

Boro River has three gates.

2 FLOOD ROUTING AND FLOW OVER GATE

SYSTEM

Flood routing is used to determine flood hydrograph

at a point based on monitored hydrograph at another

point upstream on a watercourse. Flood hydrograph

can be traced from riverbed or a dam (Soemarto,

1989). There are some flood routing methods, a well-

known one is Muskingum developed by Mc Carthy

(1938 in Ven Te Chow, 1989) as shown in Equation

(1)

tQtIS  .. (1)

where S is storage change in the i-th time interval

(m3), I is volume of inflow (m3), Q is volume

of outflow in the i-th time interval (m3), and t is

interval of duration (second, hour, day).

The foregoing equation can be elaborated as follows.

t

S
QQII nnnn




  )(

2

1
)(

2

1
11 (2)

t

H
AQQII nnnn



  )(

2

1
)(

2

1
11 (3)

HAtQQtII nnnn   .).(
2

1
).(

2

1
11 (4)

where In is inflow in the beginning of t (m3), In+1 is

inflow in the end of t (m3), Qn is outflow in the

beginning of t (m3), Qn+1 is outflow in the end of t

m3), A is the water surface area at an observed time

(m2), and is change in water elevation during t (m).

The following equation is used for flood routing

analysis through sliding floodgate.

12… ghbaKQ  (5)

where Q is discharge (m3/s), K is sinking flow

factor,  is discharge coefficient, a is floodgate-

opening (m), b is floodgate width (m), g is

acceleration due to gravity (m/s2), and h1 is depth of

water in front of floodgate above threshold (m).

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Value of K and µ for sinking flow factor and

discharge coefficient (Ministry of Public Works,

1986) are provided in Figure 1 and Figure 2,

respectively. Peak discharge is analyzed by using

rational method (Sri Harto, 2000), (Chow, 1964) as

follows

Qp = k C I A (6)

where Qp is peak discharge (m3/s), k is 0.278, C is

runoff coefficient which depends with characteristic

of the catchment area (0  C  1) (Chow, 1988), I is

rainfall intensity during time concentration

(mm/hour), and A is watershed area (km2).

Figure 1. Value of K for sink flow factor.

Figure 2. Value of  for discharge coefficient.

Kirpich (1940) developed a formula to analyze time

concentration (Chow et al, 1988) as follows.

385.0
2

.1000

.87.0














S

L
tc (7)

where tc is time concentration (hour), L is river length

(km), and S slope of the river (m/m).

3 METODOLOGICAL APPROACH

The research uses some secondary data obtained from

several source, there are Main Project of Bengawan

Solo River Region Development, Bengawan Solo

River Basin organization, and Public Works Office of

Solo (see flowchart in Figure 3).

a) Watershed map is gained from visual earth map

with scale of 1:25.000 that is resulted storage

characteristic as shown in Figure 4.

b) Daily rainfall maximum data which is used to

analyze design rainfall with specified return

period, then flood hydrograph can be presented as

in Figure 5.

c) Putat Boro watershed characteristic

d) Daily water level maximum in Jurug obtained

from AWLR.

Figure 3. Research flow chart.

0.5

0.6

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

h1/a



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Figure 4. Inundated area and storage volume of Boro River.

Figure 5. Flood hydrograph of Boro River with several

return periods.

4 RESULTS AND DISCUSSIONS

Simulation of flood analysis through Putat floodgate

applies return period of 10, 50, and 100 years and

+84.00 m maximum water level in Boro River

(Hupstream). If it is exceeded, there will be the overflow

from Boro River). Peak discharges are presented

below.

4.1.1 Inflow with a return period of 10 years

Based on 16.14 m3/s Qp Boro, + 82.50 m, + 83.00,

and + 84.00 m Boro River level, and + 82.05 m, +

82.55, + 83.48 m Bengawan Solo (Hdownstream) River

level, varying results of Putat floodgate-opening are

obtained as shown in Table 1.

Table 1. Simulation result with Qp-10 years

Hupstream

Hdownstream

+ 82.50 m + 83.00 m + 84.00 m

+ 82.05 m
0.20 m –

0.40 m

0.20 m –

0.50 m

0.20m –

0.50 m

+ 82.55 m –
0.20 m –

0.55 m

0.20 m –

0.60 m

+ 83.48 m – –
0.20m –

0.75 m

Graphic results are depicted from Figure 6 to Figure

11

Figure 6. Q10-Hupstream=82.5 m and Hdownstream=82.05 m
with variation in floodgate-opening.

Figure 7. Q10- Hupstream =83.00 m and Hdownstream =82.05 m

with variation in floodgate-opening.

0
2
4
6
8

10
12
14
16
18
20
22
24
26

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Time (hour)

Qp-2
Qp-5
Qp-10
Qp-25
Qp-50
Qp-100

Time concentration

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Figure 8. Q10- Hupstream =84.00 m and Hdownstream =82.05 m

with variation in floodgate-opening.

Figure 9. Q10- Hupstream =83.00 and Hdownstream =82.55 m
with variation in floodgate-opening.

Figure 10. Q10- Hupstream =84.00 m and Hdownstream =82.55 m

with variation in floodgate-opening.

Figure 11. Q10- Hupstream =84.00 m and Hdownstream =83.48 m

with variation in floodgate-opening.

4.1.2 Inflow with a return period of 50 years

From 21.87 m3/s Qp Boro, + 82.50 m, + 83.00, and +

84.00 m Boro River level, and + 82.05 m, + 82.55, +

83.48 m Bengawan Solo (Hdownstream) River level,

varying results of Putat floodgate-opening are

obtained as shown in Table 2.

Table 2. Simulation result with Qp-50 years

Hupstream

Hdownstream
+ 82.50 m + 83.00 m + 84.00 m

+ 82.05 m
0.2 m –

0.45 m

0.2 m –

0.55 m

0.2 m –

0.55 m

+ 82.55 m –
0.2 m –

0.60 m

0.2 m –

0.70 m

+ 83.48 m – –
0.2 m –

0.90 m

Graphic results can be seen from Figure 11 to Figure

17

Figure 12. Q50- Hupstream =82.50 m and Hdownstream =82.05 m
with variation in floodgate-opening.

Figure 13. Q50- Hupstream =83.00 m and Hdownstream =82.05 m

with variation in floodgate-opening.

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Figure 14. Q50- Hupstream =84.00 m and Hdownstream =82.05 m

with variation in floodgate-opening.

Figure 15. Q50- Hupstream =83.00 m and Hdownstream =82.55 m
with variation in floodgate-opening.

Figure 16. Q50- Hupstream =84.00 m and Hdownstream =82.55 m

with variation in floodgate-opening.

Figure 17. Q50- Hupstream =84.00 m and Hdownstream =83.48 m

with variation in floodgate-opening.

4.1.3 Inflow with a return period of 100 years

From 24.63 m3/s Qp Boro, + 82.50 m, + 83.00, and +

84.00 m Boro River level, and + 82.05 m, + 82.55, +

83.48 m Bengawan Solo (Hdownstream) River level,

varying results of Putat floodgate-opening are

obtained as shown in Table 3.

Table 3. Simulation result with Qp-100 years

Hupstream

Hdownstream
+ 82.50 m + 83.00 m + 84.00 m

+ 82.05 m
0.2 m –

0.45 m

0.2 m –

0.45 m

0.2 m –

0.60 m

+ 82.55 m –
0.2 m –

0.60 m

0.2 m –

0.70 m

+ 83.48 m – –
0.2 m –

0.90 m

Graphic are depicted from Figure 18 to Figure 23

Figure 18. Q100- Hupstream =82.50 m and Hdownstream =82.05

with variation in floodgate-opening.

Figure 19. Q100- Hupstream =83.00 m and Hdownstream =82.05 m

with variation in floodgate-opening.

Figure 20. Q100- Hupstream =84.00 m and Hdownstream =82.05 m

with variation in floodgate-opening.

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Figure 21. Q100- Hupstream =83.00 m and Hdownstream =82.55 m

with variation in floodgate-opening.

Figure 22. Q100- Hupstream =84.00 m and Hdownstream =82.55 m

with variation in floodgate-opening.

Figure 23. Q100- Hupstream =84.00 m and Hdownstream =83.48 m
with variation in floodgate-opening.

The results of simulation show that for water level of

Bengawan Solo River (Hdownstream) + 82.05 m and 10

years of Qp , the floodgate-opening that can lower

water level of Boro River maximally is 0.35 m – 0.45

m (can be seen at Figure 6, Figure 7, and Figure

8),while the floodgate-opening for 50 years of Qp is

0.40 m – 0.5 m (can be seen at Figure 12, Figure 13,

and Figure 14), and about 0.40 m – 0.55 m for 100

years of Qp (can be seen at Figure 18, Figure 19, and

Figure 20).

When Bengawan Solo elevation (Hdownstream) rises up

to + 82.55 m due to 10 years of Qp, the floodgate-

opening for maximum level reduction is

approximately 0.50 m – 0.55 m (can be seen at Figure

9 and Figure 10), 0.55 m – 0.65 m for 50 years of

Qp(see Figure 15 and Figure 16), and 0.55 m – 0.65

m for 100 years of Qp (see Figure 21 and Figure 22 ).

For + 83.48 m Hdownstream and 10 years of Qp , the

floodgate-opening that can result maximum reduction

of Boro River level is approximately 0.70 m (see

Figure 11), 0.85 m for 50 years of Qp, (see Figure 17),

and 0.85 m for 50 years of Qp (see Figure 23). If the

floodgate is opened more than those values, it may

cause backwater from Bengawan Solo River

(Hdownstream).

5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

According to the result of flood routing simulation

towards Putat Floodgate using 10 years, 50 years, and

100 years of return period of flood hydrograph with

variation in water elevation of Boro River, +82.50 m,

+83.00 m dan +84.00 m, it can be concluded that :

a) For +82.05 m Bengawan Solo Rivel level, the

effective floodgate-opening is 0.35 m – 0.55 m

b) For +82.55 m Bengawan Solo Rivel level, the

effective floodgate-opening is 0.50 m – 0.65 m

c) For +83.48 m Bengawan Solo Rivel level, the

effective floodgate-opening is 0.70 m – 0.85 m

d) Putat Floodgate can be operated with the

maximum floodgate-opening as long as no

backwater occurs

5.2 Recommendations

The followings are some recommendations to

optimize flood control system as the main goal.

a) Operating management of Putat Floodgate should

be improved by referring to the gate operational

guide.

b) Procurement of pump needs to be realized to

prevent backwater occurrence due to the overflow

from Bengawan Solo River.

REFERENCES

Chow, V.T., Maidment, M.R., and Mays, L.W.

(1988), Applied Hydrology, McGraw-Hill, New

York.

Ministry of Public Works. (1986). Standar

Perencanaan Irigasi KP-04 [Irrigation Design

Standard KP-04], Publisher Agency of Public

Works Ministry, Jakarta.

Soemarto. (1989). Hidrologi Teknik [Hydrology

Engineering], PPMTT, Malang.

Sri Harto, Br. (2000). Hidrologi – Teori, Masalah dan
Penyelesaian [Hidrology – Theory, Problems and

Solving], Nafiri, Yogyakarta.