*Corresponding author: Water Resources Engineering Department, Faculty of Engineering, Universitas Brawijaya, 65145, Indonesia E-mail address: [email protected] (Nabila Oktaviariyadi)
doi: https://doi.org/10.21776/ub.pengairan.2023.014.02.10 Received: 28-06-2023; Revised: 07-09-2023; Accepted: 29-11-2023
Vol. 14 No. 02 (2023)
Jurnal Teknik Pengairan: Journal of Water Resources Engineering
Journal homepage: https://jurnalpengairan.ub.ac.id/index.php/jtp
Original research article
Study Planning of Check Dam as Sediment Controller at Sumbersari UB Forest Area
Nabila Oktaviariyadi*, Very Dermawan , Anggara Wiyono Wit Saputra
Water Resources Engineering Department, Faculty of Engineering, Universitas Brawijaya, 65145, Indonesia
A R T I C L E I N F O A B S T R A C T Keywords:
Check Dam;
Debris Flow;
Erosion
The construction of a check dam is proposed as a solution to address multiple environmental challenges in the upstream region of a river. Primarily, the focus is on erosion control, the deceleration of debris flow, and the prevention of sedimentation. The strategic implementation of this plan encompasses a range of methodologies, including topographical measurements, geotechnical testing, hydrological analysis, hydraulics analysis, and the meticulous development of a budget plan for the actual construction of the check dam. Within the study area, sedimentation issues stem from a debris flow characterized by a sediment discharge rate of 0.657 m3/s. This phenomenon coincides with a significant 25-year return period flood discharge of 9.134 m3/s. The proposed check dam emerges as a crucial intervention capable of effectively mitigating the situation for approximately 1 hour and 13 minutes, providing a targeted response to the persisting debris flow. To execute this plan, an estimated budget of IDR 460,859,000 has been projected. This financial allocation encompasses the expenses associated with topographical measurements, geotechnical testing, hydrological and hydraulics analyses, as well as the actual construction of the check dam. Overall, the proposed check dam stands as a multifaceted solution designed to harmonize environmental conservation with sustainable water resource management.
1. Introduction
The increasing erosion rate on Earthβs land poses a significant threat due to the impact of rainwater. Data from 1984 shows that soil loss rates range from 20 to 40 tonnes per hectare per year, implying that the topsoil may be depleted within 150 years [1]. This alarming situation emphasizes the urgent need to address erosion as a critical environmental issue. Environmental changes and damage have disrupted the soil's ability to support river flows, leading to erosion processes [2]. The consequences of erosion are particularly felt in downstream areas, such as floods and landslides in cities like Batu. In Mount Arjuno, erosion has been documented at 66.24 tonnes per hectare per year [3]. Recent incidents in Batu City, including flash floods and landslides in 2021, were not solely triggered by weather factors but were also exacerbated by erosion in the upstream areas, specifically the slopes of Mount Arjuno.
Effective conservation measures are necessary to mitigate the potential impacts of erosion and reduce sediment deposition in the upstream regions [4]. One such measure is
the construction of check dams, which serve as critical infrastructure for controlling erosion and minimizing the adverse effects of sediment deposition. This study aims to design a check dam to effectively manage flood and sediment discharges. Furthermore, it seeks to evaluate the check dam's effectiveness in mitigating erosion-related issues and estimate its construction costs. The research aims to contribute to developing sustainable erosion management solutions and safeguard the studied region's balance.
2. Method
A survey of the check dam planning location was conducted in the UB forest area of Sumbersari Hamlet, Tawang Argo Village, Karangploso District, Malang Regency.
The study aimed to assess the natural conditions of the field and determine the suitable location for the check dam. The topography of the river in its original state was also considered during the survey to ensure an appropriate check dam placement. The study location can be seen in Figure 1 and Figure 2. The research was carried out in several stages.
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Figure 1. Study location
Figure 2. Study location The first step involved a site survey to determine the natural
conditions of the field, followed by hydrological calculations to obtain flood discharge data. Geotechnical testing was conducted to obtain soil physical property parameters, which were later used to calculate sedimentation. Additionally, topography measurements were taken, and hydraulics calculations were performed to determine the appropriate design for the check dam. Finally, a budget plan was calculated.
2.1. Location Survey
A survey of the intended site was conducted to determine the appropriate location for the check dam accurately. This survey aimed to assess the original field's conditions and the river's topography in that area.
By conducting this survey, the team could identify the optimal spot for constructing the check dam, considering the original terrain and the characteristics of the river.
2.2. Calculation Hydrology
The design rainfall is calculated using the flood discharge calculation method based on the Indonesian National Standard [5]. The analysis comprises several steps, including calculating the regional average rainfall, determining the annual maximum rainfall, analyzing the frequency distribution to obtain the design rainfall, conducting a frequency distribution test, and determining net rainfall and hourly rainfall distribution. In this research, one rain station that will be used is the rain station Ngujung. The calculations for flood discharge utilize the following Equation (1) and
Madura Strait
Indonesion Ocean Java Sea
East Java map Scale 1 : 1.500.000
Province of Central Java
Study Location
Equation (2):
Q = 0.2778 .C .I .A (1)
where, Q is maximum flood discharge (m3/s), C is coefficient of runoff, A is area of the drainage area (km2 ), I is average rainfall intensity (mm/hour)
I = π π‘π24 π₯ (24
π‘π 2β3
) (2)
where, R is rainfall maximum (mm), and Tc is concentration time.
2.3. Topography Map
The topographic map was obtained through field measurements along the river channel using a Sokkia brand CX Series Compact X-Ellence total station tool. The topography map is shown in Figure 2.
2.4. Geotechnical Surveying
Sampling of the land was conducted along the river channel, and soil testing was performed in the laboratory. The following tests were carried out: specific gravity test [6], content test [7], gradation analysis [8], hydrometer test [8], density test [9], and direct shear test [10].
2.5. Sedimentation Analysis
Sedimentation analysis is performed to determine the sedimentation occurring in the river channel. This sedimentation discharge is subsequently used to calculate the design discharge for the check dam. The formula used for this calculation is the Takahashi approach formula [11].
2.5.1. Debris flow
The nature of the flow, precisely debris flow, can be determined using the Takahashi approach. Use Equation (3):
tan π > πβ(πβππ€) tan β πβ(πβππ€)+ππ€ (1+β
π) (3)
where, ΞΈ is riverbed slope angle (tan ΞΈ = I = riverbed slope), β is shear angle in bed grain, c* is concentration of grains in precipitate, C* can be calculated with ( Vs/V) where Vs = solid material volume; V = water volume), Ο is debris density (tonnes/m3), ΟΟ is density of water (tonnes/m3), h is flow depth, d is average grain diameter of the riverbed surface.
2.5.2. Calculation of Transport Sediment
According to Takahashi's method, the density (Cd) of lava flow types and their volume carried by water in the river can be determined using the following Equations (4) to (6):
πΆπ = ππ .tan β
(πβππ).(tan β βtan π) (4)
πΆπ β€ 0,8 πΆ β (5)
ππ = (πΆββπΆπ).πΆπ.ππ€πΆβ (6) where, Cd is density of lava flow (tonnes/s), Qw is river flow rate (m3/s), Qs is sediment discharge (m3/s)
2.5.3. Design Discharge
The design discharge is calculated as follows Equation (7) to (9):
πΆπ = π π‘ππ π
(πβπ)(π‘ππ β βπ‘ππ π) (7)
πΌ = πΆββπΆππΆβ (8)
Figure 3. Map of check dam location
ππ = πΌ . π (9)
where, Ο is density of sediment (tonnes/m3), Ο is density of water (tonnes/m3), β is soil shear angle (Β°), ΞΈ is riverbed slope (Β°), Ξ± is coefficient of sediment content, c* is volumetric concentration of sediment in debris flow deposits, Cd is volumetric concentration of sediment in the moving debris flow, Qd is peak discharge of debris flow (m3/s), Q is flood discharge (m3/s).
2.6. Hydraulics Analysis
The hydraulics analysis of the check dam includes structural planning and an analysis of the dam's stability against overturning, sliding, and soil bearing capacity. This calculation is based on SNI 2851 [12] and SNI 2004 [13].
2.7. Cost Budget Planning
The budget plan starts with analyzing the unit price, which refers to the Regulation of the Minister of Public Works and Public Housing Number 1 of 2022 [14] and the unit price of labor [15].
3. Result and Discussion
3.1. Survey and Topography Measurement
The survey of the location and topographic measurements provided the topography map of the Bok Twin Bulk River and the location for planning the check dam, as shown in Figure 3. This location was chosen because the right bank has suitable conditions, and the left side has large rocks that would hinder the construction of the check dam. It is also the closest location to the residents and offers a larger reservoir for sediment control. Selection location is on 7Β° 49β 27.281β SL and 112Β° 34β
50.063β EL.
3.2. Geotechnical Testing
Geotechnical testing was conducted using seven types of tests in the groundwater laboratory at the Department of Water Resources Engineering, Brawijaya University, and the soil mechanics laboratory at the Department of Civil Engineering, University of Brawijaya. Ten samples of disturbed soil were used for the tests. The results of the geotechnical testing can be found in Table 1.
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Table 1. Test results for geotechnical testing
No Sample Name
Test Results Geotechnical Specific
Gravity
Bulk Density
Gradation Test and Hydrometer
Direct Shear Test Clarification Granules (%)
( gs ) (πΎ) Gravel Sand Clay Silt C β
1 Cp 6
Basic 2.532 0.923 0.000 76.000 2.380 21.620 0.166 28.44
2 Cp 6
Right 2.450 0.872 0.000 24.074 10.263 65.663 - -
3 Cp 6
Left 2.388 0.915 4.630 44.444 7.646 43.280 - -
4 Cp 9
Basic 2.657 0.940 0.000 25.301 11.978 62.721 0.058 34.24
5 Cp 9
Right 2.440 0.983 4.918 38.525 8.334 48.224 - -
6 CP 9
Left 2.316 1.128 27.011 52.299 6.717 13.973 - -
7 CP 8
Left - 1,273 9.420 63.043 0.000 27.536 - -
8 Cp 10 2.143 0.838 0.000 3.333 14.502 82.165 - -
Table 2 . Chi-Square Test summary Probability
Distribution
π₯2 Observed
π₯2 Critical Hypothesis
1% 5% 1% 5%
Gumbel 6.667 9.210 5.991 Rejected Rejected
Normal 8.667 9.210 5.991 Rejected Rejected
Normal Logs 9.333 9.210 5.991 Rejected Rejected
Log Pearson Type
III 3.333 9.210 5.991 Accepted Accepted
Table 3 . Recapitulation of Smirnov Kolmogorov Test Probability
Distribution βπ πππ₯ βπ πππ₯ πΆπ Hypothesis
1% 5% 1% 5%
Gumbel 0.714 0.404 0.338 Rejected Rejected
Normal 0.133 0.404 0.338 Accepted Accepted
Log-Normal 0.210 0.404 0.338 Accepted Accepted
Log Pearson Type
III 0.119 0.404 0.338 Accepted Accepted
3.3. Hydrological Analysis
Calculations for hydrology were customized using bulk data from 15 years of rainfall. The rainfall data was obtained from the Rain Visit station [16], [17]. Based on the calculations, a bulk analysis of the rain plan was conducted using the Normal Distribution, Normal Log, Gumbel, and Pearson III Log Methods [18], [19]. Subsequently, the suitability of the distributions was tested using the Chi-Square Test and the Smirnov-Kolmogorov Test, as presented in Table 2 and Table 3.
Tabel 2 and Table 3 shows that the distribution log pearson type III was chosen because the degrees of confidence in the vertical deviation (Chi-Square) and horizontal deviation (Smirnov Kolmogorov) were taken as the smallest [20].
Furthermore, for calculating the flood discharge, the design utilizes the rational method. This method is chosen
because the catchment area of the study area is 182.7 hectares.
According to the Ministry of PUPR [18] guidelines on sabo dam calculations, if the catchment area is less than 300 hectares, the rational method is used for flood discharge calculations, employing Equation 1. The flood discharge calculations for various return periods are summarized in Table 4.
From Table 4, the 25-year return period flood discharge value is 9.13 m3/s, which will be used to calculate the design discharge.
3.4. Analysis of Sedimentation
Sedimentation analysis is conducted to determine the type of flow occurring in the planned check dam and to calculate the design discharge [21]. The following data is used:
a) Qp (25-year return period flood discharge) = 9.134 m3/s
b) Slope of the river bed (Tan ΞΈ) = Tan 17Β°
c) The shear angle in CP 9 ( β ) = 34.24Β°
d) The density of debris mass (density test CP 9) ( Ο)
= 1.017 tonnes /m3
e) The mass density of water ( Οw) = 1 tonnes /m3
f) C* (Sediment concentration) = V/Vs = 78/0.02 = 4.034 g) d (Seedbed grain diameter Cp 9, D50) = 0.225
h) Water depth (h) = 0.5 m/s2 i) CP 9 sediment density ( Ο) = 2.470 tonnes /m3 j) The specific gravity of water ( Ο) = 0.997 tonnes /m3 3.4.1. Types of Sediment Flow
Using Equation 2, the calculation yields:
0.305 > 0.00423
Hence, the type of sediment flow occurring is a debris flow.
3.4.2. Calculation of Sediment Discharge
Sediment discharge can be calculated using equality Equation 4 and Equation 5, as follows:
The volumetric concentration of sediment in the moving debris flow or Cd is 0.064 tonnes/sec, and the peak discharge of debris flow or Qs is 0.657 m3/s.
The results of calculating the sediment discharge at each return period are presented in Table 5.
Table 4 . Calculation of the Rational Method with various return periods Return
Periode (Year)
Rainfall Tc(hour) C Rain intensity (mm/hour) Area (km2) Q (m3 /s)
2 81.16 1.20 0.542 24.893 1.83 6.85
5 94.52 1.20 0.542 28.991 1.83 7.98
10 101.19 1.20 0.542 31.037 1.83 8.54
25 108.11 1.20 0.542 33.160 1.83 9.13
50 112.31 1.20 0.542 34.448 1.83 9.48
100 115.97 1.20 0.542 35.571 1.83 9.79
Table 5. Sediment discharge calculation results at each return period Return
Periode Flood discharge Sedimentation Discharge
(Year) (m3/ s) (m3/ s)
2 6.857 0.494
5 7.985 0.575
10 8.549 0.615
25 9.134 0.657
50 9.488 0.683
100 9.798 0.705
Table 6. Recapitulation of check dam stability analysis
No Conditions Overturning Sliding
Foundation Bearing Capacity
ππ ππ
1 The forces acting on the weir flood conditions
without sediment 3.575 2.127 0.341 7.863
2 The forces acting on the weir full of sediment
flood conditions 3.029 1.864 0.484 9.357
3 The forces acting on the weir under normal
water conditions without sediment 5.945 3.226 1.247 5.448
4 The forces acting on the weir under normal
water conditions are full of sediment 4.214 2.546 0.422 6.942 5 The force acting on the weir conditions of
flooding, full of sediment, and earthquakes 1.442 1.579 1.878 5.584 6
The force acting on the weir under normal water conditions, full of sediment and earthquakes
1.506 2.546 6.139 13.504
7 The forces acting on galangal conditions are
flooded, full of sediment, and earthquakes. - 2.795 - -
8 Wall edge 4.229 1.706 13.73 24.118
190 3.4.3. Design Discharge
The debris flow hydrograph containing the sediment content at the peak of the flood can be calculated using Equations 6, 7, and 8:
Cd = 0.552 Ξ± = 1.158 Qd = 10.582 m3/s 3.5. Check Dam Design
The check dam is built with revetment having dimensions of 2 x 1 x 1 m. Revetments are used because the check dam is located in a protected forest [22], and according to Regulation of the Minister of Environment and Forestry of the Republic of Indonesia No. 8 of 2001, it is recommended to use conservation forest materials for infrastructure facilities. This calculation is based on SNI 2851 [7] and SNI 2004 [8].
The recapitulation results of the check dam design are as follows:
a. Main dam height = 3 m b. Bottom overflow width = 5 m c. Top overflow width = 6.1 m
d. Freeboard = 1 m
e. Flood water level = 1.066 m f. Crest width (b) = 2 m g. Downstream slope = 0.2
h. Upstream slope = 0.3
i. Thickness of the stilling basin = 0.5 m j. Length of the stilling basin = 6 m k. Sub dam height = 1.2 m
l. Boundary wal = 4 m
After checking the stability of the structure, the results can be calculated in Table 6. From Table 6 the design check dam was analyzed and found to be safe for overturning sliding, and bearing capacity of the foundation. Drawing results:
check dam design can be seen in Figure 4 and Figure 5.
Figure 4. Check dam top view
Figure 5. Check dam side view
Table 7. Check dam effectiveness with sediment discharge at various return periods.
Check Dam reservoir
(m3 )
Return Period (Year)
Sediment Discharge (m3/ s)
Duration (Hours)
2684.227 2 0.494 1.511
2684.227 5 0.575 1.297
2684.227 10 0.615 1.212
2684.227 25 0.657 1.134
2684.227 50 0.683 1.092
2684.227 100 0.705 1.057
Table 8. Check dam development cost planning No Work Item Unit Quantity
Unit Price (IDR)
Total Price (IDR)
A Cleaning
1 Surface clearing and stripping of soil
m2 195.42 IDR
7.713
IDR 1,507,221 2 Cut
trees/plants with a diameter of 15-30 cm
1 tree
trunk 10 IDR
26.826
IDR 268,259 3 Cut
trees/plants with a diameter of 5 -15 cm
m2 195.42 IDR
7.713
IDR 1,507,221
B Excavation
1 Soil Excavation
C Revetment
Work m3 1462.846 IDR
57.350
IDR 83,894,759 1
Revetment
installation m3 914 IDR
1,058,251
IDR 967,241,536 2
Fibers
installation m3 6 IDR
309,099
Amount IDR
460,858,144
Rounding Off IDR
460,859,000
After obtaining the check dam design parameters, the lifetime of the check dam can be calculated, as presented in Table 7. From Table 7, the duration value of the effectiveness of the check dam is obtained at 1 hour and 13 minutes.
3.6. Budget Cost Planning
The budget plan for the costs required to build a check dam is presented in Table 8. From Table 8, the budget plan required to build a check dam is IDR 460,859,000.
4. Conclusion
Based on the discussion results, the following conclusions can be drawn: The sedimentation observed during the 25-year return period flood discharge of 9.134 m3/s was classified as debris flows with a sediment discharge of 0.657 m3/s. Check dam design parameters were calculated as follows: main dam height = 3 m, bottom overflow width = 5 m, top overflow width = 6.1 m, free board = 1 m, water level during flood = 1.066 m, crest width (b) = 2 m, downstream slope = 0.2, upstream slope = 0.3, stilling basin thickness = 0.5 m, stilling basin length = 6 m, sub dam height = 1.2 m, and boundary wall
= 4 m. The design was analyzed and found to be safe for overturning, sliding, and bearing capacity of the foundation.
The check dam's effectiveness indicates that it can accommodate 2684.227 m3 of sediment without interruption if there is continuous debris flow. The check dam can hold this amount for approximately 1 hour and 13 minutes, and the budget plan required to build a check dam is IDR 460,859,000 Acknowledgment
Water Resources Engineering Department, Faculty of Engineering, Universitas Brawijaya, and all parties involved in this research.
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