rusar r%mumat rviaiuumar t%vLauciu, a I fNIVERSITI MALAYSIA SARAWAK

P. KHIDMAT MAKLUMAT AKADEMIK UNIMAS

1111111111111111111111111111 1000165786

DEVELOPMENT AND PERFORMANCE TESTS OF A SEDIMENTATION TRAP FOR SILT AND CLAY PARTICLES

PEDO ANAK EWAT

This project is submitted in partial fulfillment of the requirements for the Degree of Bachelor of Engineering with

Honours (Civil Engineering)

Faculty of Engineering UNIVERSITI MALAYSIA SARAWAK

2006

To my beloved parents

and

my siblings

i

ACKNOWLEDGEMENT

First and foremost, I would like to express my sincere gratitude to my supervisor, Ir.

Dr. Law Puong Ling, who has guided me along the whole research project and gave

me many useful theory guidance and suggestions during the process of this research.

I gratefully acknowledge all the technicians in Civil and Environmental Laboratories,

especially Mr Rozaini Ahmad, for his technical help during the preparation of

apparatus and running of experiments. Special thanks to Dr Kolay Kumar for

providing the hydrometer analysis procedure for determining the soil particle sizes

and Prof. F. J Putuhena for his advice regarding to the usage of Manning's formula.

My thanks also go to Jabatan Kerja Raya (JKR) for providing me with useful

information.

Finally, my deepest gratitude goes to my family for much love, patience and support

throughout the entire time of my study that led to the completion of this thesis.

ii

ABSTRACT

This research project focuses on the design, development and performance tests of a

sedimentation trap model regarding to its usage in civil engineering construction site

to remove or reduce the suspended solids (SS), especially for light soil particles such

as silt and clay contained in the surface runoffs. The system consists of two

components; a) the channel or drainage which is the main collecting point for the

surface runoff, and b) the sedimentation trap at which the main sedimentation

activities of suspended solids particles take place. The silt trap is divided into four

zones, namely i) Inlet Zone ii) Sedimentation/Settling Zone iii) Sludge Zone iv)

Outlet Zone. The flowrate values, Q= 3L/min and 5L/min are selected due to the

considerations on the size of the model and the apparatus for the experiment. For this

applied experimental research, it was found that at influent SS level of approximately

264 mg/L and flowrate, Q=3 L/min, the sedimentation trap would experience

sediment removal rate of approximately 23.11%; At influent SS level of

approximately 390 mg/L and flowrate, Q=3 L/min, the silt trap would operate in

approximately 17.18% sediments removal rate; and at influent SS level of

approximately 378 mg/L and Q=5 L/min, the performance of the system would be

about 12.17%. A11.14% reduction in sediment could be achieved with an influent SS

level of about 440 mg/L and Q=5 L/min.

111

ABSTRAK

Projek penyelidikan ini merupakan satu hasil kerja yang menumpukan kepada rekaan,

pembangunan dan ujian kecekapan bagi model sistem perangkap kelodak dan

lumpur. Objektif utama sistem ini adalah untuk mengurangkan dan menyingkirkan

kandungan partikel tanah terampai yang terkandung di dalam air kelodak yang

dilepaskan dari tapak pembinaan. Sistem ini terdiri daripada dua komponen; iaitu a)

terusan atau parit di mana ia berfungsi sebagai pusat pengumpulan dan laluan bagi air

kelodak yang dilepaskan dari tapak pembinaan, dan b) perangkap kelodak dan lumpur

di mana proses utama sedimentasi akan berlaku. Perangkap kelodak dan lumpur ini

dibahagikan kepada empat zon iaitu i) saluran masuk dari sistem perparitan ii) zon

sedimentasi iii) zon pengumpulan lumpur dan iv) saluran keluar. Kadar aliran air, Q=

3L/min dan 5L/min diaplikasikan di dalam eksperimen ini setelah mengambil kira

spesifikasi model dan kesesuaian peralatan eksperimen. Daripada eksperimen yang

telah dijalankan, didapati bahawa peratus kecekapan penyingkiran partikel tanah

terampai dari air kelodak bagi kepekatan ampaian permulaan 264 mg/L, 390 mg/L

dan kadar aliran air, Q=3 L/min ialah masing-masing 23.11 peratus dan 17.18

peratus. Bagi kepekatan ampaian permulaan 378 mg/L, 440 mg/L dan kadar aliran

air, Q=5 L/min, peratus kecekapan penyingkiran partikel tanah terampai ialah

masing-masing 12.17 peratus dan 1 1.14 peratus.

iv

Pusat Khldmat Nýakluruat tucademtx UfYIVERSITI MALAYSIA SARAWAK.

TABLE OF CONTENT

CONTENT

CHAPTER 1: INTRODUCTION

1.1 Overview

1.2 Objective

1.3 Specific Aims

1.4 Hypothesis

1.4.1 Sedimentation Concepts

CHAPTER 2: LITERATURE REVIEW

2.1 Overview

2.2 Silt and Clay

2.2.1 Soil in General

2.2.2 Silt

2.2.3 Clay

2.2.4 Field Tests to Identify Silt and Clay

2.3 Devices/ Apparatus to Trap Soil Particles from Construction

Site

2.3.1 Sediment Trap

2.3.2 Sedimentation Basin

PAGE

I

2

2 3

5

8

11

11

13

15

16

17

17

17

V

2.3.3 Silt Fence

2.3.4 Straw Bale Dikes/ Barriers

2.3.5 Check Dam

2.3.6 Inlet Protection

2.4 Manning Formula

18

19

20

21

22

CHAPTER 3: METHODOLOGY

3.1 Introduction 25

3.2 Design 25

3.2.1 Sizing of Sedimentation Trap for Implementation

Purpose 27

3.2.2 Plans 29

3.2.3 Estimation of Volume 33

3.2.4 Summary of Model Design Details 35

3.3 Development/ Fabrication 36

3.4 Performance Tests 38

3.4.1 Workability of Model 39

3.4.2 Determination of Manning's Roughness Coefficient, n 39

3.4.3 Procedure of Performance Tests and Samplings 40

3.4.4 Testing of Water Samples 44

3.4.5 Schematic Diagram of Experimental Procedures 45

3.4.6 Schematic Diagram illustrating Sampling and Analysis

of Samples 46

vi

CHAPTER 4: RESULTS AND DISCUSSION

4.1 Overview

4.2 Data Analysis

4.2.1 Manning's Roughness Coefficient Value, n

4.2.2 Suspended Solids Analysis

CHAPTER 5: CONCLUSIONS

5.1 Conclusions

CHAPTER 6: RECOMMENDATIONS

6.1 Limitations in the Research

47

48

48

50

60

61

6.2 Recommendations for Future Research 61

REFERENCES

APPENDIX A

Interim Water Quality Standards for Malaysia (1987)

APPENDIX B

Determination of Grain Size Distribution by Hydrometer

63

66

68

VII

LIST OF TABLES

PAGE

Table 2.1 Basic Types of Soil 12

Table 2.2 British Soil Classification System 13

Table 2.3 Field Test to Identify Silts and Clays 16

Table 2.4 Manning's Roughness Coefficients for the Design of

Improved Channels 24

Table 3.1 Estimated Side Area of Sedimentation Trap Model 33

Table 3.2 Estimated Volume of Sedimentation Trap Model 34

Table 3.3 Estimated Side Area of Actual Sedimentation Trap 34

Table 3.4 Estimated Volume of Actual Sedimentation Trap 35

Table 4.1 Section Properties of Selected Channel Sections with

Flow rate of 5.00 x 10-' m3/sec 48

Table 4.2 Section Properties of Selected Channel Sections with

Flow rate of 8.33 x 10-' m3/sec 49

Table 4.3 First Trial for Sampling with C1 = 300mg/L and

Flowrate Q=5.00 x 10-5 m3/sec 51

Table 4.4 Second Trial for Sampling with CI = 300mg/L and

Flowrate Q=8.33 x 10-' m3/sec 53

viu

Table 4.5 Third Trial for Sampling with Ct = 500mg/L and

Flowrate Q=5.00 x 10-5 m3/sec

Table 4.6 Fourth Trial for Sampling with Ct = 500mg/L and

Flowrate Q=8.33 x 10-5 m3/sec

Table 4.7 Comparison of Sedimentation Trap Removal Efficiencies

With Varying Parameters

55

57

59

ix

LIST OF FIGURES

PAGE

Figure 1.1 Existing Sedimentation Trap 3

Figure 1.2 Existing Sedimentation Trap Design 4

Figure 1.3 Upflow Settling Tank 5

Figure 1.4 Side View of Partial Solids Removal in Ideal

Sedimentation Tank 7

Figure 2.1 Revegetation of Exposed Cut Area in Road

Construction 9

Figure 2.2 Drainage Installation on the Cut Batter to Discharge

the Surface Runoff 10

Figure 2.3 Typical Structure of Silt (Granular) 14

Figure 2.4 Typical Structure of Clay 15

Figure 2.5 Silt Fence 19

Figure 2.6 Ditch Check Dam 21

Figure 2.7 Inlet Protection 21

Figure 3.1 Plan of Sedimentation Trap Model 29

Figure 3.2 Plan of Actual Sedimentation Trap With 3mx3m

Sludge Zone Area 30

X

Figure 3.3 Plan of Smaller Sedimentation Trap with 2mx2m

Sludge Zone Area. 31

Figure 3.4 Zones in Sedimentation Trap 32

Figure 3.5 Cross Sectional View of Channel 35

Figure 3.6 Fabricated Model 36

Figure 3.7 3- Dimensional View of Model 37

Figure 3.8 Sampling Locations 38

Figure 3.9 Trapezoidal Channel Section Geometric Elements 40

Figure 3.10 Mixer Tank 41

Figure 3.11 Silt and Clay Samples 41

Figure 3.12 Control valve

Figure 3.13 Water Sampling at point A

Figure 3.14 Hach DR/2400 Portable Spectrometer

Figure 4.1 First Trial (Influent Concentration, Can = 264 mg/L,

Flow rate, Q=5x 10 -' m3/sec)

Figure 4.2 Second Trial (Influent Concentration, Can = 378 mg/L,

Flow rate, Q=8.33 x 10 -s m3/sec)

Figure 4.3 Third Trial (Influent Concentration, Cm = 390 mg/L,

Flow rate, Q=5.00 x 10 -s m3/sec)

Figure 4.4 Fourth Trial (Influent Concentration, Cin = 440 mg/L,

Flow rate, Q=8.33 x 10 -' m3/sec)

42

43

44

52

54

56

58

XI

LIST OF CHARTS

PAGE

Chart 3.1 Schematic Diagram of Experiment Procedures 45

Chart 3.2 Schematic Diagram Illustrating Sampling and 46

Analysis of Samples

XII

LIST OF ABBREVIATIONS

C- Concentration

DO - Dissolved Oxygen

DOE - Department of Environmental

G- Gram

h- depth

L- Liter

m- Meter

ml - Mililiter

mm - Milimeter

min - Minutes

NREB - Natural Resources and Environmental Board

NTU - Nephelometry Turbidity Unit

N- Manning's Coefficient of Roughness

P- Wetted Perimeter

Pa - Pascal

Q- Flowrate/ Discharge

R- Hydraulic Radius

r- Radius

sec - Second

SS - Suspended Solids

X111

USEPA - United States Environmental Protection Agency

UV - Ultra Violet

y- Water Depth Normal to the Bottom of Channel

V- Velocity

Vr _ Settling Velocity

°C- Degree Celsius

µ- Micro

71 - pi

- Percentage

xiv

CHAPTER I

INTRODUCTION

1.1 Overview

At present, silt trap is one of the options to control the release of suspended

solids, mainly silt and clay particles from the construction site to the rivers and

streams. Sand particle is rarely taken into the consideration due to its high weight

ratio compared to the silt and clay particle and the settling path is shorter. A

proper control on the release of these particles into the river is important and

critical to preserve the natural condition of the river and streams. The release of

silt and clay particles into the river in vast amount can cause rapid settlement on

the river bed and reduce the depth of the river and will cause flooding. High total

suspended solids concentration in the river can block light from reaching

submerged vegetation. As the amount of light passing through the water is

reduced, photosynthesis slows down. Reduced rates of photosynthesis causes less

dissolved oxygen to be released into the water by plants. If light is completely

blocked from bottom dwelling plants, the plants will stop producing oxygen and

will die. As the plants are decomposed, bacteria will use up even more oxygen

from the water. Low dissolved oxygen can lead to fish kills. High concentration of

total suspended solids can also cause an increase in surface water temperature,

because the suspended particles absorb heat from sunlight. This can cause

I

dissolved oxygen levels to fall even further (because warmer waters can hold less

DO), and can harm aquatic life in many other ways (Mitchell and Stapp, 1992).

1.2 Objective

The objective of this research project attempts to develop a more reliable

sedimentation trap especially for silt and clay with special application to road

construction activities in the tropics. The main consideration for the application is

during the rainy season when an overflow case is considered.

1.3 Specific Aims

The primary components of the proposed system consist of 1) Inlet Zone, 2)

Sedimentation/Settling Zone, 3) Outlet Zone, and 4) Sludge Zone. This research

project focuses on relatively more effective design, development and performance

tests of a pilot scale sediments removal system. The system is suitable for

sediment loaded surface runoffs resulted from road construction activities such as

fill and cut areas.

The specific aims of this project are to:

i. Develop a pilot scale "sedimentation trap" model suitable for fill and cut

surface runoffs loaded with suspended solids especially silt and clay;

ii. Determine removal efficiencies of suspended solids such as silt and clay

by using overflow case; and

iii. Optimize system removal efficiencies by adjusting, changing, or

manipulating design and operating parameters.

2

1.4 Hypothesis

Natural Resources and Environment Board, Sarawak (NREB) and

Department of Environment, Malaysia (DOE) currently accepted an existing

design of a sedimentation trap as a "suitable silt trap" for control of silt and clay

particles from being discharged into rivers and streams for a road construction

project. Figure 1 (a & b) and Figure 2 show the detailed design of an existing

sedimentation trap that is currently in use.

Current field studies on the performance of the existing sedimentation trap

found that those sedimentation traps are generally non-functional or serve very

little purpose for removal of silt and clay especially when overflow condition is

considered during the rainy season.

Figure 1.1 : Existing Sedimentation Trap.

Recently, NREB environmental control officials reviewed that the

department would welcome and adopt any alternative sedimentation trap of

different designs, provided that the design is certified by a registered

civil/environmental professional - Professional Engineer Registration with BEM.

3

fTHTT

- Z- öv

I

ý3 INLET

MIN) 111 EXCAVATED EARTH CHANNEL PLAN STREAM (SEE NOTE 2) PLAN

0 2m

SAND FILLING

I Is

NUMBER OF GASIONS TO SUIT STREAM OUTLET

OUTLET 0

10 m LENGTH (MINI b EXCAVATED EARTH CHANNEL

STREAM (SEE NOTE 2)

IRE BOX GABION WITH ROCKFILL

RIV-V I ýý ý

A

I J

GEOTEXTILE FABRIC POLYFELT TS65 .. J

OR EQUIVALENT

SECTION C-C

o2 m SILT TRAP ON FLAT GROUND

SIZE OF SILT TRAP TABLE i DIMENSION

L(m) 3.0 4.0

5.0

W (m) 3.0 4.0 5.0

BS SIEVE SIZE % PASSING BY WEIGHT 10.0 mm 100 5.0 mm 90-100

1.18 mm 45-80 300 um 10-30 150 um 2-10

NOTES 1. SAND FOR FILLING SHALL HAVE A GRADATION COFORMING TO THE ENVELOPE SHOWN IN

TABLE 1. 2. THE CONTRACTOR SHALL PROPOSE THE SECTIONS FOR EARTH CHANNELS UP STREAM AND

DOWN STREAM OF PROPOSED SILT TRAPS ON FLAT OR SLOPING GROUND FOR A LENGTH OF AT LEAST 10 METRES EACH. ONCE APPROVED BY S. O. THEY SHALL BE EXCAVATED AND MAINTAINED BY THE CONTRACTOR AND THE COSTS SHALL BE DEEMED TO BE INCLUDED IN THE RATES FOR CONSTRUCTION AND MAINTENANCE OF SILTTRAPS.

3. EXISTING GROUND SLOPE SHALL BE TRIMMED ACCORDINGLY TO RECEIVE THE GEOTEXTILE FABRIC, SAND FILL AND GABIONS.

Figure 1.2: Existing Sedimentation Trap Design.

4

1.4.1 Sedimentation Concepts

The design of the proposed sedimentation trap would take into considerations

both the design (shape/structure) parameters and collections principles of gravity

settling chamber, i. e., sediment loaded runoffs are directed through an oversized

section where horizontal velocity drops low enough (while vertical velocity

remains the same) to let silt particles settled by gravity.

Two important terms that need to be considered in sedimentation zone design

is the particle settling velocity, vs and the second term is the overflow rate vo. The

overflow rate is the velocity at which the tank is designed to operate. Consider an

upward flow sedimentation tank as shown in the figure on the next page.

Surface Area = As \4

T

Liquid

/_, r

Its

f Settled Particles

ý-1 I--ý Liquid Floms rate =Q

Vo Overflow rate =-

A

1 Particles + Liquid

Figure 1.3: Upflow Settling Tank.

The particles will fall downward and the water rises vertically. In order for

the settling of particles to happened in the clarifier, the particle settling velocity

must be greater than the liquid rise velocity (vs > vo). As stated earlier in clause

1.4.1 (paragraph 3), If v., is greater than vo one would expect 100 percent particle

5

removal and if vs is less than vo one would expect 0 percent removal. For the

vertical settling tank, the term overflow rate is used since the water is flowing

over the top of the tank into the weir system and it is sometimes referred to as the

surface loading rate because it has units of m3/d. m2. This can be thought of as the

amount of water that goes through each m2 of tank surface area per day, which is

similar to a loading rate. From the equation below, an overflow rate is the same as

a liquid velocity:

Volume / Time (Depth)(SurfaceArea) Depth vo =__= Liquid Velocity (Eq. 1.9)

SurfaceArea (Time)(SurfaceArea) Time

From the equation above it can be seen that in vertical settling tank is

independent of the depth of the sedimentation tank.

An ideal horizontal sedimentation tank is based upon three assumptions ( A.

Hazen, 1904 & T. R. Camp, 1946).

1) Particles and velocity vectors are evenly distributed across the tank cross

section. This is the function of the inlet zone.

2) The liquid moves as an ideal slug down the length of the tank.

3) Any particle hitting the bottom of the tank is removed.

In a horizontal sedimentation tank, unlike an upflow clarifier, some

percentage of the particles with vs less than vo will be removed. For example,

consider particles having a settling velocity of 0.5 va entering uniformly into the

settling zone. Figure 3-26 shows that 50 percent of these particles (those below

half the depth of the tank) will be removed. That is they will hit the bottom of the

tank before being carried out because they only have to settle one-half the tank

depth. Likewise, one-fourth of the particles having a settling velocity of 0.25 v,,

will be removed.

6

50 %

50 %

i -01. ý ý ý ý

I ý ý AN. ý -00.

Escaped

Captured

Figure 1.4: Side View of Partial Solids Removal in Ideal Sedimentation Tank.

7

CHAPTER 2

LITERATURE REVIEW

2.1 Overview

In a tropical environment, "soil is moved primarily by runoff associated with

rainfall, thus, erosion is defined as the movement of soil particles either

individually or as aggregates, downslope as a result of the waterflow" (Crighton

and Tomkins, 2000). Erosion and sedimentation from construction of roads,

highways, and bridges, and from unstabilized cut-and-fill areas, can significantly

impact surface waters and wetlands with silt and other pollutants including heavy

metals, hydrocarbons, and toxic substances. Erosion and sediment control plans

are effective in describing procedures for mitigating erosion problems at

construction sites before any land-disturbing activity begins (U. S. Environmental

Protection Agency, 2005).

At present, methods of minimizing soil erosion and sedimentation of water

bodies (i. e., rivers and streams) for roadway/highway construction projects in the

State of Sarawak include some of the followings:

i. Minimize clearing to within 3m from the top of cut butters and within 5m

of the bottom of the road.

ii. Carry out directional felling so that tree fall into the road clearing area to

minimize damage to adjacent vegetation.

8

iii. Stockpile topsoil for later use in revegetation.

iv. Carry out progressive revegetation of exposed area in tandem with slope

stabilization work.

Figure 2.1: Revegetation oC Exposed Cut Area in Road Construction.

v. Retain a 50m buffer strip of vegetation fringing rivers within which

borrowed areas, spoil dumpsites and clearing (expected at stream

crossings) or dumping of vegetation is prohibited.

vi. During cut and fill operations, all fill areas must be firmly consolidated

and compacted.

vii. Both cut and fill batters should be turfed or hydroseeded as soon as

possible,

viii. Larger and/or steeper cut or fill batters must be terraced and provided with

appropriate drainage installation to discharge surface runoff.

9