1. The Second International Conference on
Sustainable Infrastructure and Built Environment (SIBE-2013)
Bandung, Indonesia – November 19th – 20th 2013
A 3-Dimensional Numerical Study of Flow Patterns around
Three Types of Drop Spillway
Dantje K. Natakusumah1
, Dhemi Harlan 2
, Fitra Adinata3
, Waluyo Hatmoko4
, Ade
Khairani Tobing5
, Muhammad Juangga6
dan M. Rizki Kusmaryadi7
1,2
Water Resources Engineering Research Group, Institute of Technology Bandung
3
PT Sapta Adhi Pratama, Bandung
4
Water Resources Research Center, Ministry of Public Works, Bandung
5,6,7
Water Resources Engineering Graduate Students, Institute of Technology Bandung
Email: 1
dkn@si.itb.ac.id
Abstract. Traditionally the behaviors of hydraulic structures are studied using
scaled physical models constructed in hydraulic laboratories. In general these
approaches are expensive, time-consuming and often subject to error due to
difficulties associated with scaling effects. With the advance in computer
graphics, computer technology and more efficient Computational Fluid
Dynamics (CFD) algorithm, the behavior of hydraulic structures can now be
investigated numerically in reasonable time and expense.
This paper describes the CFD modeling of three type of drop spillway in three-
dimension. FLOW3D3 software which solves the Navier-Stokes equation by the
finite difference method, use the algorithm based on SOLA method while the
Volume of Fluid (VOF) method was used for computing free surface motion. In
this analysis FLOW3D was applied to numerically solve the Navier-Stokes
equations for solution domains around three types of drop spillways each of
which is modeled into single region. Depending of complexity and the number of
grid poits of the spillway model, numerical simulation by using FLOW3D on
personal computer can takehours to a few days. Much shorter than scaled
physical models constructed in hydraulic laboratories
In this preliminary paper, the calculated results such as pressure, velocities, flow
rate, surface height have not been validated against experimental data. The work
on that direction is now underway. In conclusion, the results obtained using
numericalmodel in terms of velocity patterns, local flow disturbances, discharge
rate, surface height distribution and Froude number can be easily obtained for
further used for engineering design purpose.
Keywords: Drop Spillway, FLOW3D, Numerical model, Hydraulics
1 Introduction
One of the main functions of the spillway is to pass water from a high elevation
to low elevation place to lower one. Due to the elevation change, the potential
energy turns into kinetic energy and directing the flow of water moving at a
certain speed. Another function of the spillway is to reduce the kinetic energy of
water through the spillway so that the speed at the end of spillway becomes
smaller. Damping occurs either as a result of collisions with rigid bodies of
water or due to collisions among the particles of water in the whirlpool, causing
partial loss of kinetic energy of the flow.

2. 2 Dantje K. Natakusumah et.al
In conventional spillway energy dissipation took place in a horizontal direction,
by the collision with vertical plane (e.g baffle piers) and resulting turbulence. In
the conventional spillway, Water flow through the spillway crest and chute
channel, only relatively small energy is reduce by friction. However, upon
entering the energy dissipator, the energy flow will be broken down by chute
block and most of kinectic energy will be dissipate by baffle piers and water
turbulence. Finally the water flow will be levelled by end sill.
The initial idea for developing drop spillway studied in this research, started
from experience of the main author, when he design a detention pond located in
LIPO Cikarang. At the outlet of detention pond a conventional WES spillway of
16 meters crest lenght and 4 meters high and a USBR-III stilling basin has been
prepared for the contruction. Since the construction cost of the original design
was quite high, and the available land is limited, the original design was
replaced with a new design, the drop spillway , we name it type I drop
spillway, connected with the box culvert. This spillway can significantly reduce
the construction costs and require much smaller space. Based on this success,
some impovement and changes have been made, until we arive at the concept of
the drop spillway I, T and U type.
2 Methodology
In this paper, we present some preliminary results on hydraulic characteristics
testing of 3 types of drop spillway known as drop spillway I-Type, T-Type and
U-Type. This 3D numerical study was performed using FLOW3D software.
FLOW-3D is a general-purpose computational fluid dynamics (CFD) software.
FLOW3D is based on the Navier Stokes equations which consists of a three-
dimensional continuity equation, momentum equation and energy equation 3-
dimensional fluid.
Detailed description on how to solve the equation is beyond the scope of this
paper, and the interested reader is referred to the FLOW3D User technical
refference [4]. However, it can be explained that FLOW3D employs specially
developed numerical techniques to solve the equations of motion for fluids to
obtain transient, three-dimensional solutions to multi-scale, multi-physics flow
problems. An array of physical and numerical options allows users to apply
FLOW-3D to a wide variety of fluid flow and heat transfer phenomena.
The problem of flow with free of water surface is a particular challenge in 3D
numerical models. The Volume of Fluid (VOF) method developed by Hirth [1]
is employed in FLOW-3D for this purpose. It consists of three main
components: the definition of the volume of fluid function, a method to solve
the VOF transport equation and setting the boundary conditions at the free
surface.
Flow-3D using structured and orthogonal grid with a rectangular shape (2D)
and hexahedral cells (3D). Calculation grid is fixed (non-adaptive) and do not
move during the process of calculation. Boundary between air and objects
defined by the method of Fractional Area Volume Obstacle Representation
(FAVOR). As surface of water moves, the grid will also move vertically.
Therefore, only the water phase will be counted, not the air phase [2].

3. A 3-D Numerical
3 Results and Disscusion
In this paper, some preliminary results on numerical modeling of three drop
spillway, known as drop spillway
spillway are intended for embung. Embung is local name for a small dam with
water stroring capacity less than 500 thousand m
km, embankment height less than 10 meters and it is built on firm soil and low
permeability soil.
Figure 1 shows 3 types of drop spillways
These drop spillway
constructed in two stages. Using stage construction, the costs of construction
can be distributed in stage. It starts with low cost low height dam and when
addional fund is available, the constructi
stop the operation of embung built in the earlier stage. According to the
regulation, development of small embung like this, does not require dam
certification process.
Figure 1: Perspective
Numerical Study of Three Types of Drop Spillway
Results and Disscusion
some preliminary results on numerical modeling of three drop
spillway, known as drop spillway I-Type, T-Type and U-Type. These drop
spillway are intended for embung. Embung is local name for a small dam with
water stroring capacity less than 500 thousand m3, dam crest lengt less than 1
km, embankment height less than 10 meters and it is built on firm soil and low
3 types of drop spillways investigated in this research
pillway are planned to be built in conjuction of embung
constructed in two stages. Using stage construction, the costs of construction
can be distributed in stage. It starts with low cost low height dam and when
addional fund is available, the construction can be continue without having to
stop the operation of embung built in the earlier stage. According to the
regulation, development of small embung like this, does not require dam
Perspective View of Drop Spillway I-Type, T-Type and U-
Three Types of Drop Spillway 3
some preliminary results on numerical modeling of three drop
. These drop
spillway are intended for embung. Embung is local name for a small dam with
3, dam crest lengt less than 1
km, embankment height less than 10 meters and it is built on firm soil and low
in this research [3].
are planned to be built in conjuction of embung
constructed in two stages. Using stage construction, the costs of construction
can be distributed in stage. It starts with low cost low height dam and when
on can be continue without having to
stop the operation of embung built in the earlier stage. According to the
regulation, development of small embung like this, does not require dam
-Type

4. 4 Dantje K. Natakusumah et.al
3.1 Drop Spillway I-Type
The first type of spillway modeled numerically using FLOW3D is I-Type drop
spillway. The dam embankment is planned to be built in two stages, where in
the Stage-1, 5-meter embankment is constructed. At Stage -2, additional 5 meter
embankment construted behind the stage-1 embankment. Development of
Stage-1 to Stage -2 can be done without without having to stop the operation of
embung built in the earlier stage.
Perspective view of I-Type drop Spillway at the first and second stage are
shown in figure Figure 2.a). Crest Lenght in both stages is 10.0 meter, but
Crest Elevastion has ben raised from elevation +3.0 m to elevaton +7.0 m. The
following results were obtained when flood dicharge of 20 m3/s pass over the
spillway crest. Figure 2.b) shows perspective view of velocity around I-Type
drop spillway at the first and second stage. Figure 2.c) shows detailed
perspective view of velocity around I-Type drop spillway at the first and second
stage. Figure 2.d) shows velocity contour and vector of of velocity around I-
Type drop Spillway at the first and second stage. Finally a more detailed :
Numerical Results of 3D Drop Spillway I-Type is given in Table 1.
Table 1 : Numerical Results of 3D Drop Spillway I-Type
No Computed Values Unit Stage-1 Stage -2
1 Discharge m3/s 20 20
2 Crest Lenght m 10 10
3 Crest Elevastion m +3.0 +7.0
4 Weter Level at the stilling basin m +0.0 +0.0
5 Weter Level at the reservoar m +7.66 + 11.94
6 Water Depth Above the Crest m 0.64 0.72
7 Velocity in the middle of the crest m/s 2.8 2.5
8 Velocity at the mid of stilling basin m/s 2.8 2.5
9 Weter Depth at mid the basin m 2.32 3.085
10 Velocity at the start Box Culvert m/s 4.39 2.2
11 Depth at the start Box Culvert m 2.32 3.085
12 Velocity at the end Box Culvert m/s 6.95 5.254
13 Depth at the end Box Culvert m 2.2 2.9
3.2 Drop Spillway T-Type
The Second type of spillway modeled numerically using FLOW3D software is
T-Type drop spillway. Perspective view of T-Type drop Spillway at the first
and second stage are shown in figure Figure 3.a). Crest Lenght in both stages is
10.0 meter, the crest Elevation of the spillway has ben raised from elevation
+3.0 m to elevaton +7.0 m. The following results were obtained when flood
dicharge of 20 m3/s pass over the spillway crest. Figure 3.b) shows perspective
view of velocity around T-Type drop spillway at the first and second stage.
Figure 3.c) shows detailed perspective view of velocity around T-Type drop
spillway at the first and second stage. Finally Figure 3.d) shows velocity
contour and vector of of velocity around T-Type drop Spillway at the first and
second stage. Finally a more detailed Numerical Results of 3D Drop Spillway I-
Type is given in Table 2.

5. A 3-D Numerical Study of Three Types of Drop Spillway 5
Table 2 : Numerical Results of 3D Drop Spillway Tipe-T
No Computed Values Unit Stage-1 Stage -2
1 Discharge m3/s 20 20
2 Crest Lenght m 10 10
3 Crest Elevastion m +3.0 +7.0
4 Weter Level at the stilling basin m +0.0 +0.0
5 Weter Level at the reservoar m +7.86 +11.97
6 Water Depth Above the Crest m 0.79 0.95
7 Velocity in the middle of the crest m/s 4.845 2.55
8 Velocity at the mid of stilling basin m/s 1.625 2.55
9 Weter Depth at mid the basin m 2.66 4.13
10 Velocity at the start Box Culvert m/s 4.31 7.75
11 Depth at the start Box Culvert m 1.73 1.84
12 Velocity at the end Box Culvert m/s 6.46 7.75
13 Depth at the end Box Culvert m 1.41 1.14
3.3 Drop Spillway U-Type
The first type of spillway modeled numerically using FLOW3D is U-Type drop
spillway. Perspective view of U-Type drop Spillway at the first and second
stage are shown in figure Figure 4.a). Despite their curved shape, Crest Lenght
in both stages is 10.0 meter, but the Crest Elevastion has ben raised from
elevation +3.0 m to elevaton +7.0 m. The following results were obtained when
flood dicharge of 20 m3/s pass over the spillway crest. Figure 4.b) shows
perspective view of velocity around U-Type drop spillway at the first and
second stage. Figure 4.c) shows detailed perspective view of velocity around
U-Type drop spillway at the first and second stage. Finally Figure 4.d) shows
velocity contour and vector of of velocity around T-Type drop Spillway at the
first and second stage. Finally a more detailed Numerical Results of 3D Drop
Spillway U-Type is given in Table 3
Table 3 : Numerical Results of 3D Drop Spillway Tipe-U
No Computed Values Unit Stage-1 Stage -2
1 Discharge m3/s 20 20
2 Crest Lenght m 10 10
3 Crest Elevastion m +3.0 +7.0
4 Weter Level at the stilling basin m +0.0 +0.0
5 Weter Level at the reservoar m +7.83 +11.771
6 Water Depth Above the Crest m 1.05 1.034
7 Velocity in the middle of the crest m/s 3.53 2.95
8 Velocity at the mid of stilling basin m/s 4.69 8.8
9 Weter Depth at mid the basin m 3.35 2.01
10 Velocity at the start Box Culvert m/s 5.17 2.95
11 Depth at the start Box Culvert m 1.86 2.23
12 Velocity at the end Box Culvert m/s 5.17 5.9
13 Depth at the end Box Culvert m 1.48 1.46

6. 6 Dantje K. Natakusumah et.al
a) Perspective view of I-Type drop Spillway
b) Perspective view of Velocity Around I-Type drop Spillway
c) Detailed Perspective view of Velocity Around I-Type drop Spillway
d) Velocity Contour and Vector of of Velocity Around I-Type drop Spillway
Figure 2 : Simulation Resuls of I-Type drop Spillway

7. A 3-D Numerical Study of Three Types of Drop Spillway 7
a) Perspective view of T-Type drop Spillway
b) Perspective view of Velocity Around T-Type drop Spillway
c) Detailed Perspective view of Velocity Around T-Type drop Spillway
d) Velocity Contour and Vector of of Velocity Around T-Type drop Spillway
Figure 3 : Simulation Resuls of T-Type drop Spillway

8. 8 Dantje K. Natakusumah et.al
a) Perspective view of U-Type drop Spillway
b) Perspective view of Velocity Around U-Type drop Spillway
c) Detailed Perspective view of Velocity Around U-Type drop Spillway
d) Velocity Contour and Vector of of Velocity Around U-Type drop Spillway
Figure 4 : Simulation Resuls of U-Type drop Spillway

9. A 3-D Numerical Study of Three Types of Drop Spillway 9
4 Research Benefits
Small dam and dry detention pond both have almost similar shape, in the form
of hollow ground which is usually a small river valley and dammed the building
is equipped with spillway and outlet expenses can be arranged. Although small
dam and dry detention pond has almost the same shape, but they have different
functions.
 Small dam function to save rainwater to be used for a variety of uses (e.g.
agricultural, domestic or industrial). Thus the small dam is almost always
filled with water and empty only if the water supply has been used up.
Function as small dam of water-use and water conservation infrastructure
for various needs
 Dry detention pond serves to hold the flood discharge of the river basin is
relatively small, with spending set saved flood water through the outlet can
be set in order for the downstream location of the dry detention pond area
was not flooded. Function is as a dry detention pond handling of destructive
force of water infrastructure.
One benefit of this research can also be seen from the fact that many former pit
coal mines are scattered in various locations in East Kalimantan and South
Kalimantan. Besides the former tin mine often found in Bangka Belitung
province, mined bauxite is also often found on the island of Bintan, Riau Islands
Province. Conversion pits into ponds for water conservation will solve one
environmental problem arising after mining operations were closed. Utilization
of pits water can only be done if the water in the pit can be controlled.
Controlling water in the former mines can only be done by deepening outlet
mined by digging or raise water by damming part of the land around the pit
outlet and then install the spillway and water level control.
Another benefit of this research can also be seen from the fact that many
residential areas and industrial areas, frequently flooded due to lack of
infrastructure gor controlling runoff. According to regulations, the developer is
actually required to make flood control infrastructure, where one of them is a
conventional reservoir. Conventional flood control infrastructure is not popular,
because it takes a lot of areas and they cannot be used for other activities, since
they filled with water.
To overcome the reluctance of developers to build a conventional detention
pond, recently developed a new idea to create a dry detention pond. When there
is no rain reservoar pool is not filled with water, or only slightly flooded, thus
the location of the dry detention pond can be used as a green area where the
morning sports area taking place. When it rains, substantial portion reservoir
pond will be filled with water, but they will gradually recede because the water
is gradually released through an outlet reservoir dry.
5 Conclusion
Simulation results on the drop spillway I-Type, T-Type and U-Type shows
realistic results. The results obtained were able to show the magnitude of
velocity, thickness of water, turbulent energy and dissipation energy in almost
all parts of spillway from upstream to downstream..

10. 10 Dantje K. Natakusumah et.al
This kind of detailed results, althouh can still be obtained in the physical model,
it will require much longer time, both to acquire the raw data and to process it
into a variable such as turbulent energy, energy dissipation and the Froude
number that cannot be measured directly. The test results of drop spillway I-
Type, T-Type and U-Type shows that the numerical model has its advantages
which can give results much faster and relatively cheaper, the physical model
requires a much longer time and are more expensive.
Spillway physical model testing needs to be done immediately for the most
promising shape, according to the numerical results that will be performed at
the Laboratory of Physical Hydraulic Model Testing, Civil Engineering ITB.
Currently physical models of the most promising forms are still in progress.
6 Acknowledgements
The authors express gratitude to Directorate General of Higher Education and
research that has provided funding through the DIKTI Decentralization of
Higher Education Research Program 2013. The authors also express our
gratitude to the LPPM-ITB who had been monitoring the implementation of the
study.
7 References
[1] C. W. Hirt And B. D. Nichols, Volume of Fluid (VOF) Method for the
Dynamics of Free Boundaries, Journal Of Computational Physics 39,
201-225 (1981)
[2] Hossein Afshar, Seyed Hooman Hoseini, Experimental and 3-D
Numerical Simulation of Flow over a Rectangular Broad-Crested Weir,
International Journal of Engineering and Advanced Technology (IJEAT),
ISSN: 2249 – 8958, Volume-2, Issue-6, August 2013
[3] Dantje K. Natakusumah,Pembuatan Protoptye, Pengujian Modek Fisik
Dan Model Numerik Tiga Dimensi Untuk Pelimpah Terjunan Tipe I,
Tipe T Dan Tipe U Serta Penggunaanya Pada Konstruksi Kolam Tandon
Kering (Dry Detention Pond) Dan Konstruksi Embung (Small Dam,
Proposal Riset Desentralisasi DIKTI, 2013).
[4] FLOW3D, User Manual, Flow Science, Inc, 2013.