EROSION AND SEDIMENT YIELD EVALUATION IN REGARDS OF EROSION SEDIMENT CONTROL PRACTICES (ESCP)
SITI ISMA HANI BINTI ISMAIL
UNIVERSITI SAINS MALAYSIA
2010
ACKNOWLEDGEMENT
“IN THE NAME OF GOD, THE MOST GRACIOUS, THE MOST
COMPASSIONATE”
Alhamdulillah, I thought the time to write this section would never arrive, and often I even wondered why I’d ever decided to start on my Masters. Now I’ve reached the end and it is time to express my gratitude to all the people who have encouraged me to finish this work.
For sure, the fulfillment of this research is due to the cooperation of many people. Therefore
I can only hope that I mention you all and those who I forget at this moment please forgive me and think that despite this lapse I really do appreciate you all
I would like to begin by saying how greatly indebted I am to The Almighty Allah S.W.T for giving me the strength, patience and never ending courage in completing my research.
I would like to take this golden opportunity to dedicate this report with grateful thanks to my dearest parents and parents in law, En. Ismail Bin Haji Omar, Puan Siti Eshah Binti Haji
Hasan, En. Asbullah Bin Latif and Puan Sabrinawati Binti Abdullah for their continuous supports during this thesis preparation. My sincere gratitude and love goes to my beloved husband, En. Anuar Shamsuri Bin Haji Asbullah who made it possible for me to embark on my research.
I would like to express my sincere and million thanks to my supervisor, En Zorkeflee Bin
Abu Hasan for his priceless guidance, suggestions, supportive advice, constructive criticism and encouragement all the way through this study project. Without him I would not be able to complete this research. On the other hand, I am also grateful to my second supervisor Dr.
H. Md. Azamathulla for his idea and assistance.
ii I would like to offer my special thanks and appreciate to my boss, Mr. Lim Man Kwang, my consultants Ir Tang Heap Seng and Ir Yeap Geok Ngoh, Professor Dr. Nor Azazi Zakaria,
Dr. Lai Sai Hin, Profesor Dr. Roslan Zainal Abidin, Puan Nurul Azfa Binti Azizan, Cik Noor
Hasliza Binti Wan Chik, Cik Nuramidah Binti Hamidon, En Zubir Bin Mohammed, En.
Nassir, Puan Norsalina Binti Johari, Noor Arbaayah bin Mohd. Hashim and Puan Noor
Zamrina Binti Zakaria for their guidance and supports throughout my research.
I would like to thank those researchers in the field of erosion modeling and processes from different countries around the world that unselfishly provided their findings, software and publications, thus greatly contributing to my research.
Last but not least to all my friends for their endless support and encouragement throughout the years of my studies. Finally to all the individuals who were involves in the mission to complete this thesis, thank you again from the bottom of my heart.
May all the good deeds that were done will be blessed by ALLAH S.W.T.
iii TABLE OF CONTENTS
CHAPTER CONTENT PAGE
ACKNOWLEDGEMENT ii
TABLE OF CONTENTS iv
LIST OF TABLES viii
LIST OF FIGURES xii
LIST OF PLATES xvi
LIST OF ABBREVIATIONS xvii
LIST OF SYMBOLS xix
ABSTRAK xx
ABSTRACT xxi
CHAPTER 1 – INTRODUCTION 1.0 General 1 1.1 Background 3 1.2 Study area 11 1.2.1 Rational for Selection of Study Area 12 1.3 Problem statement 13 1.4 Objectives 17 1.5 Research Significance 18 1.6 Research Report Outline 18
CHAPTER 2 - LITERATURE REVIEW 2.0 Introduction 20 2.1 Definition of Soil Erosion 21 2.1.1 Why does erosion occur? 24 2.1.2 How does erosion occurs 24 2.1.3 Type of Erosion 27 2.1.4 Erosion and Sediment Hazards Associated with Development 33 2.1.5 Factors that Influence Erosion 37 2.1.6 Best Management Practices 39
iv 2.1.7 Erosion and Sediment Control Practices (ESCP) 41 2.1.8 Sediment Delivery Ratio (SDR) 41 2.2 Existing Model Review/Model types 42 2.2.1 Universal Soil Loss Equation (USLE) and Modifications 45 2.2.2 Revised Universal Soil Loss Equation (RUSLE) 45 2.2.3 Agricultural Non-Point Source (AGNPS) 46 2.2.4 Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS) 46 2.2.5 The Chemical Runoff and Erosion from Agricultural Management Systems (CREAMS) 46 2.3 Weirs 47 2.4 Discussion and Conclusion 48
CHAPTER 3 - STUDY AREA AND METHODOLOGY 3.0 Introduction 49 3.1 Study Area 49 3.1.1 Landuse / Development 50 3.1.2 Topography 51 3.1.3 Soil Types 52 3.1.4 Drainage and Hydrology 53 3.1.5 Flooding Conditions 54 3.1.6 Climate and Meteorology 55 3.2 Methodology 56 3.2.1 Desk Study 57 3.2.2 Research Preparation 66 3.2.3 Field work / Data collection 67 3.3 Data analysis and overall brief discussion 96
CHAPTER 4 - DATA COLLECTION AND ANALYSIS 4.0 Introduction 100 4.1 Data Analysis 100 4.1.1 To measure water level of dry sedimentation ponds during Storm events 100 4.1.2 To measure Inflow and Outflow of dry sedimentation Pond B by using the Rectangular Sharp Crested Weir 109 4.1.3 To check the Total Suspended Solid (TSS) of Inflow and Outflow of dry sedimentation Pond B 115
v 4.1.4 To estimate soil erosion rates for study area 119 4.2 Summary 151
CHAPTER 5 – RESULTS AND DISCUSSION 5.0 Introduction 152 5.1 Dry Sediment Pond designs on the study area 152 5.2 Measured water levels of dry sedimentation ponds during the storm events 156 5.3 The measured Inflow and Outflow of Dry Sedimentation Pond B By using Rectangular Sharp Crested Weir 163 5.3.1 Measured Water Level versus Time 163 5.3.2 Weirs’ discharge rate versus Time 164 5.3.3 Required Storage Volume for Pond B during storm events 167 5.3.4 Runoff volume (m3) and peak runoff rate per event (m3/s) 168 5.4 Total Suspended Solid (TSS) at Inflow and Outflow of dry sediment Pond B 169 5.4.1 Summary of the efficiency of the ESCP 174 5.5 Evaluation of the soil erosion rates at study area 175 5.5.1 Assessment of soil erosion rates by using Modified Soil Loss Equation (MSLE) and Revised Universal Soil Loss Equation (RUSLE) 176 5.5.2 Assessment of soil erosion rates at Pond B by using Modified Soil Loss Equation (MUSLE) Equations versus measured Erosion rates (TSS) 179 5.5.3 Assessment of soil erosion rates at Pond B by using MUSLE by William and Berndt (1977) compared to RUSLE and MSLE Equations 186 5.5.4 Assessment of soil loss rates at Pond B by using MUSLE Equation and measured erosion with Sediment Delivery Ratio (SDR) 188 5.6 Conclusion 189
CHAPTER 6 - CONCLUSIONS AND RECOMMENDATIONS 6.0 Introduction 191 6.1 Conclusion 191 6.1.1 Estimation and evaluation of the soil loss on the study area 192
vi 6.1.2 Comparison of various equations used by researchers for soil loss evaluation 193 6.1.3 Efficiencies of the ESCP used on the study area 194 6.2 Recommendation 195 6.3 Summary and Concluding 196
REFERENCES 198
APPENDICES
APPENDIX A Dry Sedimentation Pond Designs
APPENDIX B Measured Water Levels for Pond A, B, C, D and
E during the storm events for the year of 2008
APPENDIX B (i) Value for V (m3) for Pond A
APPENDIX B (ii) Value for V (m3) for Pond B
APPENDIX B (iii) Value for V (m3) for Pond C
APPENDIX B (iv) Value for V (m3) for Pond D
APPENDIX B (v) Value for V (m3) for Pond E
APPENDIX C Measured water levels at the Rectangular Sharp Crested
Weir (Inflow and Outflow) and the hydrograph for weir
discharge
APPENDIX D Total Suspended Solid (TSS) calculation
APPENDIX E Erosion calculation by using MSLE, RUSLE and MUSLE
Equations
APPENDIX F Soil Investigation - Boreholes results
vii
LIST OF TABLES
TABLE TITLE PAGE
1.1 Population Distribution and Yearly Average Growth Rate 6 Percentages for Penang According to District from 1980 to 2000
1.2 Migration distribution according to State, 1995 to 2000 7 (Interim Reports on Penang State Structure Plan (2005- 2020))
1.3 Housing Development in Penang, 1991 to 2000 (Interim 9 Reports on Penang State Structure Plan (2005 to 2020))
1.4 Estimated Demand for Residential Land 2000 - 2020. 9
1.5 Projection of the Development Land needed for 10 Residential by Sector for every 5 Year, Penang (Hectare)
1.6 Major impact of soil erosion failures for on-site and off- 10 site scenarios (Goh and Tew, 2006)
1.7 Landuse Suitability at the study area (Geotechnical 13 Report, 2006)
2.1 Erosion/Sediment transport models (Merritt et al. 2003) 43
3.1 Rainfall Data for Year 2008 (MMD, 2008) 56
3.2 Terrain classification (Geotechnical Report, 2006) 63
3.3 Percentage of OM content for 26 Malaysian Soil Series 81
3.4 Soil Structure (S) Class and Code for 26 Malaysian Soil 82 Series
3.5 Soil Permeability (P) Class and Code for 26 Malaysian 83 Soil Series
3.6 Exponent m based on slope percent (FRIM, 1999) 86
3.7 C Factor and P Factor values for construction site rainfall BMPS 89
4.1 MSMA - Sediment Basin Types and Design 101 Consideration (DID, 2000a)
4.2 MSMA - Dry sediment basin sizing Guideline (DID, 101 2000a)
viii
TABLE TITLE PAGE
4.4 Sediment basin size required based on MSMA guideline 103 (DID, 2000a)
4.5 Summary of the Dry Sediment Pond designs on study site 105
4.6 Example of volume calculated for Pond A and Pond B on 107 the study area
4.7 Example of daily water level measured at Pond A, B, C, D 109 and E
4.8 Examples of water level measurement at Inflow and 113 Outflow of weirs for discharge (Q) value (dated 10th May 2008)
4.9 Typical water sampling laboratory results for TSS (June 116 2008)
4.10 Water sampling laboratory results for TSS value for the 117 month of October 2008
4.11 Extract of the Meteorological Data for 4th October 2008 118
4.12 Summary of the TSS results at Pond B 119
4.13 K factor at Boreholes 1 to 22 on the study area 125
4.14 LS Factor at the study area for Boreholes 1 to 22 126
4.15 Soil Loss estimation by using MSLE equation for 128 Boreholes 1 to 22 on the study area
4.16 Soil loss rates by using RUSLE equation for Boreholes 1 130 to 22 at the study area
4.17 Percentage (%) different in Soil Loss estimation by using 131 MSLE and RUSLE at the Boreholes 1 to 22
4.18 Extract of the Meteorological Data based on water 133 sampling dates
4.19 EI30 value for Onstad and Foster (1975) 134
4.20 Summary of total runoff rate per event and peak runoff 136 rate per event for Pond B
4.21 K and LS Factor for MUSLE equations for Pond B 137
ix
TABLE TITLE PAGE
4.22 Soil loss rate by using MUSLE equation by Onstad and 138 Foster (1975) at Pond B
4.23 Soil loss rate by using MUSLE equation by William and 141 Berndt (1977) at Pond B
4.24 Soil loss rate by using MUSLE equation by Fifield (2004) 142 at Pond B
4.25 EI30 value and soil loss rate by using MUSLE equation by 143 Tew and Goh (2006) at Pond B
4.26 Summary of erosion rates at Pond B by using the MUSLE 145 equations versus TSS
4.27 Soil loss rates for Pond B by using RUSLE and MSLE 147 equations
4.28 Soil loss rates comparison between MUSLE with RUSLE 148 and MSLE
4.29 SDR for erosion estimation by using the MUSLE 150 equations
5.1 Dry sedimentation pond sizing and designs 153
5.2 The maximum height and pond’s capacity designed 158
5.3 Measured water levels on 8th Mac 2008 and 22nd April 158 2008 which exceeded the maximum allowable height of the sedimentation ponds
5.4 Extract of Rainfall data from the Meteorological Data on 162 8th of Mac 2008 and 22nd of April 2008
5.5 Extract of Rainfall data from the Meteorological Data on 167 6th of September 2008
5.6 The summary of the required storage volume for Pond B 168
5.7 TSS results for the water samples at Inflow and Outflow 169 of Pond B
5.8 The variable K Factor and LS Factor for soil erosion 177 evaluation using the MSLE and RUSLE
5.9 Summary of erosion rates comparison using the MSLE 178 and RUSLE equation
5.10 Classification of the Soil Erosion Rate (Department of 179 Agriculture, 2008)
x
TABLE TITLE PAGE
5.11 Classification of the Soil Erosion Rate (Hardy, 2004) 179
5.12 The erosion rates comparison obtained from various 181 MUSLE equations with measured erosion for Catchment B
5.13 The percentage of soil loss volume for MUSLE equations 185 and TSS
5.14 Soil loss estimation using the MUSLE, RUSLE and 187 MSLE equations for Pond B
5.15 Sediment Delivery Ratio (SDR) for each of the MUSLE 189 equations
xi LIST OF FIGURES
FIGURE TITLE PAGE
1.1 Physical Topographical of Penang (Penang Structure Plan 4 2005 – 2020)
1.2 Landuse in Penang Year 2004 (Penang Structure Plan 5 2005 – 2020)
1.3 Population distribution for Penang according to district, 7 1980 to 2000 (Interim Reports on Penang State Structure Plan (2005-2020)
1.4 Location map of the study area 12
1.5 Artist illustrations on land development impact on Soil 15 Erosion(Connecticut Guidelines for Soil Erosion and Sediment Control, 2002)
1.6 The research work flow 19
2.1 The GLASOD estimate of global land degradation 23
2.2 A simple model of hillside erosion (Merritt et al., 2009) 25
2.3 Types of erosion ((A) Encyclopedia Britannica, 2006) and 27 (B) Lal, 1990)
2.4 The five types of Soil Erosion on an exposed slope 29 Source: North Carolina DEHNR, 1993
2.5 The direct impact of falling drops of rain on soil particles 30
2.6 Changes in the runoff due to urbanization 34
2.7 Typical pre-development and post-development discharge 35 rates
2.8 Changes in stream hydrology as a result of urbanization 36 (Schueler, 1992)
2.9 Factors influencing erosion potential 39
2.10 Sharp Crested Weirs 48
3.1 Location of the study area 50
3.2 Survey plan of the research area (Geotechnical Report, 51 2007)
xii
FIGURE TITLE PAGE
3.3 Cross Section Profile for the site plan (Geotechnical 52 Report, 2007)
3.4 Soil Map of the Project Area (EIA, 2007) 53
3.5 Flow chart showing the four phases in conducting the 57 research
3.6 Topography Plan for the study area 59
3.7 Example of particles size distribution from the SI Report 61
3.8 Boreholes Location of the study area (SI Report, 2006) 62
3.9 Terrain Map of the study area (Geotechnical Report, 63 2006)
3.10 Building consideration by following land profile 64 (Geotechnical Report, 2006)
3.11 Work flow for the data collection segment 66
3.12 Typical Dry Detention Basin Components (DID, 2000) 68
3.13 Site plan showing all the pond location and the receiving 68 catchment area
3.14 Form used for the data collection of the water level 70 reading at Pond A to Pond E
3.15 Type of weirs 71
3.16 The location of the ‘ruler’ at the weirs 73
3.17 Form used for data collection at the weirs 73
3.18 Annual Rainfall Erosivity (R) map for the Penang State of 80 Malaysia (Shamshad et al. 2007)
3.19 Nomograph for Soil Erodibility (K) factor 84
3.20 Soil texture triangle for determining soil texture 85
3.21 RUSLE equation and its factors influencing Soil Erosion 88 and Sedimentation
3.22 Rainfall Erosivity analysis flow chart 91
3.23 Example of runoff hydrograph 93
xiii
FIGURE TITLE PAGE
3.24 Water level measurement at the dry sedimentation ponds 97
3.25 Nixon-Steramflo and the Current Meter 98
4.1 Dry sedimentation pond sizing and detail design 104
4.2 Graph showing the volume versus water level measured 108 on the study area
4.3 Example of volume estimation for the water level 110 measurement
4.4 A typical Rectangular Sharp Crested Weir (Bentley 110 Systems, 2007)
4.5 Rectangular Sharp Crested Weir with end contractions 111 and its section (DID, 2000b)
4.6 Graph showing the measured water level versus time for 114 Pond B
4.7 Typical example of graph for flow discharge versus time 115 for Pond B
4.8 Annual Rainfall Erosivity (R) map for the Penang State of 121 Malaysia (Shamshad et al. 2007)
4.9 SI analysis report for Boreholes 11 122
4.10 Soil Erodibility Nomograph (Foster et al., 1981) 123
4.11 Diagram used to calculate the LS value 124
4.12 Catchment area B divided into two zones based on the 132 boreholes location
4.13 The total runoff rate calculation 135
5.1 Sediment pond and cross section 154
5.2 Water flows from higher level to lower level 155
5.3 Illustration of check dam located inside the earth drain 156
5.4 Typical graph for volume versus measured water level for 157 Pond A
5.5 Typical effect on the impervious area for land 161 development
xiv
FIGURE TITLE PAGE
5.6 Rainwater effects on surface runoff 162
5.7 Rectangular Sharp Crested Weir 163
5.8 Typical graphs for measured water level versus time at the 164 weirs from May 2008 to December 2008
5.9 Typical hydrograph of Q versus time at Inflow and 165 Outflow of Weirs from May 2008 to December 2008
5.10 The Inflow hydrograph is smaller compared to the 166 Outflow hydrograph on 6th September 2008
5.11 Peak discharge rate and the total runoff volume for the 168 hydrograph
5.12 Suspended solid (TSS) trend at Pond B 170
5.13 National Water Quality Standard for Malaysia (DOE, 171 2006)
5.14 DOE Water Quality Index Classification and Uses (DOE, 171 2006)
5.15 Maintenance access for typical Sedimentation Basin 172 Layout
5.16 Cross section showing the storage capacity is reduced due 173 to sediment accumulation
5.17 Potential significant environmental impact on surface 174 water during construction
5.18 Localized Deposition of particles before entering Pond B 183
5.19 Emergency spillway at Pond B 184
5.20 Use of Sediment Basin on construction sites 190
xv
PLATE TITLE PAGE
1.1 Typical example of Soil Erosion features on construction 16 site
2.1 Soil Erosion Phenomena on bare slope 20
3.1 Historical flood surrounding the study area due to surface 55 runoff
3.2 Pictures showing the site plan before the land 60 development
3.3 Dry Sedimentation Ponds on study area 69
3.4 Pictures showing the water level measurement at the 70 sedimentation ponds
3.5 The construction of weirs at the study area 72
3.6 Weirs and ‘ruler’ located at the Inlet and Outlet of Pond B 73
3.7 Water level measurement and water sampling at Pond B 74
3.8 Water samples 76
3.9 Laboratory Works for TSS 77
4.1 Pond B 105
4.2 Pond A 105
5.1 A ‘ruler’ was placed inside the sediment pond for 156 measuring purposes
5.2 Poor maintenance work for the sediment ponds 159
5.3 Receiving drain after heavy rain 159
5.4 Maintenance works is carry out at the receiving drain after 159 heavy rain
5.5 Uncontrolled site clearing activities 160
5.6 Failed side slope at Pond B 173
xvi LIST OF ABBREVIATIONS
AGNPS Agricultural Non-Point Source Pollution Model
ANSWERS Areal Nonpoint Source Watershed Environment Response
Simulation
ARI Average Recurrence Intervals
ASML Above Sea Mean Level
BLIA Bayan Lepas International Airport
BMP Best Management Practices
CREAMS The Chemical Runoff and Erosion from Agricultural
Management Systems model
DID Department of Irrigation and Drainage
DOA Department of Agricultural Malaysia
DOE Department of Environmental
ECP Erosion Control Plan
EIA Environmental Impact Assessment
EMP Environmental Management Plan (EMP)
EPA Environmental Protection Agency
ESCP Erosion Sediments Control Practices
EWRC Environment Waikato Regional Council
F.R. Forest Reserves
FAO Food and Agriculture Organization of the United Nation
FRIM Forest Research Institute Malaysia
GIS Geographic Information Systems
GLEAMS Groundwater Loading Effects of Agricultural Management
Systems
LESTARI The Institute for Environment and Development
MDRN Missouri Department of Natural Resources
xvii MMS Malaysia Meteorological Services Department
MPPP Majlis Perbandaran Pulau Pinang
MSC Multimedia Super Corridor
MSLE Modified Soil Loss Equation
MSMA Manual Saliran Mesra Alam
MUSLE Modified Universal Soil Loss Equation
NC DEHNR North Carolina Department of Environment, Health and Natural
Resource
NSW New South Wales
NWQSM National Water Quality Standard of Malaysia
PERFECT The Productivity, Erosion and Runoff, Functions to Evaluate
Conservation Techniques
RMSE Root Mean Square Error
RUSLE Revised Universal Soil Loss Equation
SIR Storie Index Rating
SWAT Soil and Water Assessment Tools
TIA Traffic Impact Assessment
TSS Total Suspended Solids
UNEP/GPA United Nations Environment Programme/Global Programme of
Action
USDA United States Department of Agriculture
USEPA United State Environment Protection Agency
USLE Universal Soil Loss Equation
WEPP Water Erosion Prediction Project
WQI Water Quality Index
xviii LIST OF SYMBOLS
SYMBOLS DESCRIPTIONS Ηx Measured height A Erosion rate for RUSLE B Weir base width
CSCW Constant for Rectangular Sharp Crested Weir E Rate of erosion for MUSLE EI Rainfall Erosivity index H Head above weir crest excluding velocity head Hc Height of the weir until the bottom of the opening
I30 Rainfall intensity for 30 minutes IA Fraction of impervious area K Soil Erodibility Factor LS Slope Length Factor m Exponent n Number of end contractions for weir OM Organic Matter P Annual rainfall Q Weir discharge qc Erosion Rate for MSLE
QP Peak runoff rate per event
qP Peak flow rate R Rainfall Erosivity RO Total runoff rate per event for MUSLE S Soil structure code T Sediment yield per storm event TSS Total Suspended Solid V Volume of runoff VM Vegetation management factor Constant for MUSLE
2 Constant for MUSLE
xix PENILAIAN HAKISAN DAN HASILAN ENDAPAN BERKAITAN DENGAN
AMALAN KAWALAN HAKISAN ENDAPAN
ABSTRAK
Tapak projek pembinaan adalah terdedah kepada risiko hakisan air disebabkan oleh aktiviti kerja tanah yang giat dijalankan. Bagi tapak pembinaan ini, didapati cerun bukit terdedah begitu sahaja tanpa sebarang tanaman dan sistem pemparitan yang sedia ada pula dipenuhi dengan hasilan endapan. Hasilan endapan ini akan menyebabkan peningkatan ketara bagi beban endapan ke kawasan tadahan sungai manakala teknik pembinaan yang digunakan turut menyumbang kepada pencemaran di kawasan sekeliling tapak pembagunan ini. Hakisan yang berlaku di tapak kajian adalah disebabkan oleh aktiviti penebangan pokok, keamatan lebat hujan yang tinggi dan juga kegagalan kolam endapan untuk berfungsi dengan berkesan.Kajian ini dijalankan untuk menilai hakisan dan hasilan endapan yang disebabkan oleh hujan lebat dan air larian di tapak kajian yang terletak di Sungai Ara, Pulau Pinang,
Malaysia. Jumlah kehilangan tanah ditentukan dengan menggunakan kaedah permodelan empiric bagi hakisan iaitu Revised Universal Soil Loss Equation (RUSLE), Modified Soil
Loss Equation (MSLE) dan Modified Universal Soil Loss Equation (MUSLE) dan juga berdasarkan kepada sampel yang telah diambil di kawasan kajian. Keputusan kajian menunjukkan kadar hakisan dan enapan adalah tinggi bagi kawasan kajian ini. Kadar hakisan tahunan tertinggi adalah direkodkan di Lubang Jara 19 melalui persamaan RUSLE iaitu sebanyak 7,772 ton/hektar/setahun. Dengan menganalisa sampel yang diambil di Kolam
Endapan B, keputusan beban enapan terampai (TSS) yang diperolehi melalui aliran masuk ke kolam enapan adalah diantara 352 mg/l sehingga 5031 mg/l manakala di aliran keluar pula mencatatkan nilai diantara 309 mg/l ke 5375 di mana kesemua nilai ini diklasifikasikan sebagai Kelas V bagi Jabatan Alam Sekitar Malaysia. Walaubagaimanapun, berdasarkan sampel yang telah diambil, didapati kadar kehilangan tanah adalah jauh berkurangan jika dibandingkan dengan kaedah pengiraan kehilangan tanah.
xx EROSION AND SEDIMENT YIELD EVALUATION IN REGARDS OF
EROSION SEDIMENT CONTROL PRACTICES (ESCP)
ABSTRACT
During construction, large areas of soil are exposed to the risk of water erosion due to earthworks activities. Bare slopes and drains choked with sediment can often be observed on construction sites. This erosion may result in a significant increase in sediment loads to receiving waters and the construction techniques used on site can cause offsite contamination. Erosion from the study area occurred due to the removal of the vegetation cover, high rainfall intensity and the failure of the sediment basins to function effectively.
The present study aims to evaluate the erosion and sediment yield due to storm rainfall and runoff on a construction site located at Sungai Ara, Penang state of Malaysia. The soil loss was evaluated by using empirical erosion modelling namely the Revised Universal Soil Loss
Equation (RUSLE), Modified Soil Loss Equation (MSLE) and Modified Universal Soil Loss
Equation (MUSLE) and from the water samples taken at the study area. Results showed that large amount of sediment has being eroded from the study area. The highest annual erosion rates estimated is by using the RUSLE equation is recorded at Borehole 19 with soil loss of
7,772 tons/ha/y. By analyzing the samples collected at the Pond B, the TSS value is noted from 352 mg/l to 5031 mg/l at Inflow and 309 mg/l to 5375 mg/l at Outflow which fall under the Class V according to the classification by Department Of Environment in Malaysia.
However, the results shows that the measured soil loss was very much smaller compared to the calculated soil loss.
xxi CHAPTER 1
INTRODUCTION
1.0 General
In Malaysia, township and urban areas were rapidly developed. By the 1970s, urbanization and industrialization touched most of the country. As a result, land became an increasingly scarce resource in many of the developed areas such as Kuala Lumpur, Petaling Jaya,
Penang and Johor Bahru. In the last ten years, intensification of industrialization, housing and construction, the development of tourism and agriculture, and greater urbanization have led to greater pressure on land. Even land reclamation (in some coastal areas) has not eased the pressures as demand for land remains high. As such, developers have turned to developing hill land (Ibrahim et al., 2002).
Hill land, which is located on the upstream of drainage basins, is extremely sensitive to human induced environmental changes (Ibrahim et al., 2002). Even small changes caused by forest clearance could lead to severe damage on natural systems such as flora, fauna, climate, hydrology and soils (Ibrahim et al., 2002). Rapid development of the foothills, slopes and hill tops since the 1970s, have resulted in depletion of forest, destruction and deterioration of water catchments, changes in micro climatic elements, endangering of wild life, high rates of soil erosion, increased incidence of landslide and rock-falls, high rates of sedimentation leading to rapid siltation and reduce capacities of rivers leading to an increased frequencies and magnitudes of downstream flooding (Chan, 1998), besides the pollution of the river water (Ibrahim et.al. 2002).
1 In line with vision 2020, Malaysia has undergone tremendous land development, especially in the development of infrastructures. Although these activities form an integral part of the socio economic advancement in this country, their success is indeed limited, if insufficient attention is paid to the adverse effects of land development particularly on soil erosion issues
(Faisal and Tew, 2006).
As all of us are aware, degradation of the non-renewable soil resource by accelerated (human sinduced) erosion is a serious environmental problem (Sutherland, 1989). Accelerated erosion results from agriculture, mining and any activities related to urbanization, such as building construction, utility development and road building (Wolman and Schick, 1967;
Anderson and McCall, 1968; Guy and Jones, 1972; Reed, 1980). Goldman et al. (1986) stated that when land is disturbed for construction, road building, mining, logging, landscaping or other activities, the soil erosion rate increases from two to forty thousand times. Construction areas are of particular concern because they are considered to be one of the most severe modifications of the human landscape (Meyer, et al., 1971). It was reported by Fifield (2008) and North Carolina Department of Environment, Health, and Natural
Resources (NC DEHNR) (1993) that erosion rates at construction sites may be ten to twenty times greater than for undisturbed lands. Over a short period of time, construction sites can contribute more sediment to receiving streams than was previously deposited over several decades (NC DEHNR, 1993).
On the other hand, studies in the Auckland region shows that construction sites yield ten to hundred times more sediment than untouched land (Associated Rockery Contractors (ARC)
1992; The Auckland Regional Authority (ARA) and Auckland Regional Water Board
(ARWB), 1983; Swales 1989).
2 In engineering perspective, soil erosion is defined as a general destruction of soil structure by the action of water and wind (Beasley, 1972). It is essentially the smoothing process with soil particles being carried away, rolled and washed down by the force of gravity (Morgan,
1993). Rainfall is the prime agent of soil erosion, whereby the rain’s runoff will scour away, loosen and break soil particles and then carry them away, thus leaving behind an altered bare earth surface (Wischmeier et al., 1978). In the case of a slope, an altered bare surface of the slope with the formation of sheet, rill and gully erosion features will cause instability of the slope. This situation will gradually cause slope failure or landslide as commonly known. The soil erosion phenomenon is basically the function of the erosivity of the rainfall and the erodibility of the soil (Roslan, 1992). In other words, when the rainfall acts upon the earth surface, the amount of the soil erosion loss will basically depend upon the combination of the strength and the magnitude of the rainfall to cause the erosion process and the ability of the soil to withstand the rain itself (Hudson, 1979).
1.1 Background
The Penang state of Malaysia has made remarkable progress in its economic development over the past few decades. The diversification of the economy from agricultural sector into manufacturing sector has meant rapid urbanization and industrialization. Bayan Baru and
Bayan Lepas Industrial Estates were established since 1969 (Penang Development News,
2003) to boost the economic growth in the island. George Town has been extended and became a regional hub for Northern Region of Malaysia. Following the impetus for economic expansion, comes the related demand for manpower especially in the fields of manufacturing and commercial businesses. Since then, the influx of population from other states to Penang has contributed to the greater growth of its population.
Increasingly, land is a scarce resource which is much sought after in Penang Island,
Malaysia. This is because Penang is largely made up of steep topography and much of the lowland areas are already been developed as shown in Figure 1.1 and Figure 1.2.
3 Figure 1.1: Physical Topographical of Penang (Penang Structure Plan 2005 – 2020) Source: Penang Structural Plan, 2005 – 2020
4 Figure 1.2: Landuse in Penang Year 2004 (Penang Structure Plan 2005 – 2020) Source: Penang Structural Plan, 2005 – 2020
5 Penang is one of the many rapidly industrializing states in Malaysia with a largely urban populace. In recent decades, efforts at industrialization and the development of other economic sectors have been intensified, leading to greater urbanization and greater pressures on land (Chan, 1998). The rapid urbanization and industrialization has also accelerated its impact on the hydrology and geomorphology of the island. The tremendous increase in the population of the island due to internal migration and influx of people from other countries such as Indonesian and Bangladeshi, seeking jobs in the island’s industries, have caused and increased demand for more land for development of housing estates as shown in Table 1.1,
Figure 1.3 & Table 1.2. The intention of the State Government to make Penang the leading industrial state in Malaysia has also caused more flatlands to be developed for industrial use
(Ismail, 1997).
Table 1.1: Population Distribution and Yearly Average Growth Rate Percentages for Penang According to District from 1980 to 2000 (Interim Reports on Penang State Structure Plan (2005-2020))
Yearly Average Growth 1980 1991 2000 Rate (%) District 1980 - 1991 - 1980 - Population % Population % Population % 1991 2000 2000 North East 391,400 43.5 395,714 37.2 444,923 33.9 0.1 1.31 0.6 South 76,390 8.5 122,764 11.5 169,442 12.9 4.4 3.7 4.1 West Northern Main 199,449 22.1 224,647 21.1 259,823 19.8 1.1 1.6 1.3 Land Central Main 161,975 18.0 236,270 22.2 313,607 23.9 3.5 3.2 3.4 Land Southern Main 71,558 7.9 84,771 8.0 125,654 9.6 1.6 4.5 4.5 Land Penang 900,772 100 1,064,166 100 1,313,449 100 1.5 2.4 1.9
Source: Department of Statistic Malaysia, 2002
6 Population Distribution Population 500,000
400,000
300,000
200,000
100,000
0 1980 1991 2000 Year
North East South West Northern Seberang Perai Central Seberang Perai Southern Seberang Perai
Figure 1.3: Population distribution for Penang according to district, 1980 to 2000 (Interim Reports on Penang State Structure Plan (2005-2020) Source: Department of Statistic Malaysia, 2002
Table 1.2: Migration distribution according to States, 1995 to 2000 (Interim Reports on Penang State Structure Plan (2005-2020))
State 1995 2000 Net Net Migrate In Migrate out Migrate In Migrate out Migration Migration Selangor 78,005 40,370 37,635 60,941 36,637 24,304 Penang 24,436 11,925 12,511 29,735 15,077 14,658 Johor 22,387 24,471 (2,084) 31,522 18,146 13,376 Terengganu 11,689 15,913 (4,224) 19,953 11,519 8,434 Melaka 13,224 10,961 2,263 9,688 9,507 181 Kedah 18,798 17,943 855 22,530 23,143 (613) Negeri 23,535 15,438 8,097 16,293 17,100 (807) Sembilan Perlis 2,897 2,484 413 1,832 3,567 (1,735) Pahang 17,218 25,488 (8,270) 17,908 19,720 (1,812) Sarawak 8,133 9,709 (1,576) 9,284 12,066 (2,782) Perak 15,975 36,346 (20,371) 20,711 27,656 (6,945) Sabah 12,685 11,615 1,070 13,147 21,079 (7,932) Kelantan 22,406 17,679 4,727 12,846 21,422 (8,576) Kuala 14,137 45,183 (31,046) 4,459 34,200 (29,741) Lumpur
Source: Migration Investigation Report, 1995 – 2000, Department of Statistic Note: ( ) Means a negative value
Although land reclamation has eased the pressures somewhat, it is not enough to satisfy the high demand for land on the island. Due to its small size of 285 km2 in area and lack of flat land, developers have turned to the remaining hill land on the island. Many hills and their
7 environs are already being developed and many hill projects are in the pipe line (Ismail,
1997), which is very common in Penang Island nowadays. As all of us are aware, construction industries are the backbone of any land development and it growths rapidly as well. The immediate response that will come across our mind of any construction development is the negative impacts to the adjacent areas or downstream such as deforestation, decimation of water catchments, destruction of endangered fauna and flora, soil erosion, landslides, water pollution, sedimentation and downstream flooding. Some of these problems have been exacerbated and turned into disasters due to the extremely fragile and sensitive nature of hill ecosystems. Despite such problems, the State Government has decided to lift the freeze on development of hill land since January 1998 and this has effectively opened up all hill land for development on the island (Chan, 1998).
As a result of growing population comes a corresponding need for adequate housing. It is projected that between the year 1996 to 2010, an average of 3,800 housing units are required annually in the island (Majlis Perbandaran Pulau Pinang (MPPP), 2007). Table 1.3 and Table
1.4 shows the Housing Development and Land demand in Penang. However, the figure is expected to increase by taking into account those immigrants from other States. As to hasten development and accelerate the pace towards Vision 2020, the housing woes must first be solved. To deal with the issue, there must be concerted efforts by the private and public sector to reduce the present housing shortage and to satisfy future housing needs. The objective of housing development as outlined in the Penang Island Structure Plan (1989) is to ensure an adequate housing provision at an appropriate location accompany with range of utilities, social amenities and recreational facilities as tabulated in Table 1.5.
8 Table 1.3: Housing Development in Penang, 1991 to 2000 (Interim Reports on Penang State Structure Plan (2005 to 2020))
Percentage of Residential Unit Unit Increments increments (%) District 1991 - 1995 - 1991 - 1995 - 1991 1995 2000 1995 2000 1995 2000 Northeast 79,631 99,530 130,612 19,899 31,082 25.0 31.2 Island Southwest 26,562 32,927 44,847 6,365 11,920 24.0 36.2 Total 106,193 132,457 175,459 26,264 43,002 24.7 32.5 Northern 48,112 52,300 58,779 4,188 6,479 8.7 12.4
Main Central 55,618 66,565 83,940 10,947 17,375 19.7 26.1 Land Southern 19,550 23,307 34,648 3,757 11,341 19.2 49.7 Total 123,280 142,172 177,367 18,892 35,195 15.3 24.8 Total for Penang 229,473 274,629 352,826 45,156 78,197 19.7 28.5
Source: Department of Statistic Malaysia Special Request, 2000 & Penang Structural Plan, 2005 - 2020
Table 1.4: Estimated Demand for Residential Land 2000 - 2020.
2000 – 2005 2006 - 2010 2011 - 2015 2016 - 2020 Total
Land Land Land Land District % Land Amount Area Amount Area Amount Area Amount Area Amount Area (Ha) (Ha) (Ha) (Ha) (Ha)
10
Northeast 40
50
Total Island 10 78 5.2 234 15.6 286 19.1 598 39.9
40 312 4.2 935 12.6 1,145 15.5 2,392 32.3 Southwest 50 391 2.6 1,168 7.8 1,432 9.5 2,991 19.9
Total 781 12.0 2,337 36.0 2,863 44.1 5,981 92.1 10 26 1.7 146 9.7 178 11.9 350 23.3
40 104 5.0 584 27.8 711 33.9 1,399 66.7 Northern 50 130 1.1 731 5.8 888 7.1 1,749 14.0
Total 260 7.8 1,461 43.3 1,777 52.9 3,498 104.0 10 120 8.0 336 22.4 456 30.4
40 480 22.9 1,346 64.1 1,826 87.0 Main Central Land 50 601 4.9 1,682 13.5 2,283 18.4
Total 1,201 35.8 3,364 100.0 4,565 135.8 10 29 1.9 236 15.7 265 17.6
40 114 5.4 946 45.0 1,060 50.4 Southern 50 142 1.1 1,183 9.5 1,325 10.6
Total 285 8.4 2,365 70.2 2,650 78.6 Total 1,041 19.8 5,284 123.5 10,369 267.2 16,694 410.5
Source: Penang Structural Plan, 2005 - 2020
9 Table 1.5: Projection of the Development Land needed for Residential by Sector for every 5 Year in Penang (Hectare)
Land Usage 2000 – 2005 2006 - 2010 2011 - 2015 2016 - 2020 Total Residential 0 20 124 267 411 Business 211 254 316 444 1,225 Industrial 302 565 565 570 2,002 Community Facilities 691 198 311 269 1,469 & Recreations Total 1,204 1,037 1,316 1,550 5,107
Source: Penang Structural Plan, 2005 - 2020
As all of us are aware, the construction activities usually cannot be done without disturbing the existing plants, trees, soil and rocks under the ground. Problems often occur when soil is put aside for a short time, used to fill holes or low areas, or removed from the area. Other problems might occur from careless handling of construction materials or fuels on-site.
Nutrients, trace metals and hydrocarbons seep into the ground from leaking containers or spills. During storm events, these contaminated soils may be carried away from the construction site. When these soil particles settle out, they become a source of pollution to the downstream water bodies (Fifield, 2008). Some of the adverse effects of soil erosion are as shown in Table 1.6.
Table 1.6: Major impact of soil erosion failures for on-site and off-site scenarios (Goh and Tew, 2006)
Locations Effects of soil erosion failures • Loss of value, productivity and services from affected land • Undermining of roads and utilities • Sediment and mud on roads with associated traffic problems and road safety issues • Clogged drains and increased nuisance flooding On-site • Sedimentation and bank damage on construction sites • Increased down time on construction and building sites after storm events • Unsightly appearance of construction works • Accelerated sedimentation and excessive soil loss • High cost of reconstruction and maintenance
10 • Sedimentation in nearby reservoirs and other storage structure, with resulting loss of water storage capacity • Instability of stream channels nearby caused by increased runoff and sediment loads • Reduction in channel capacity leading to greater frequency of floods caused by siltation and sedimentation of rivers • Proliferation of exotic weeds within watercourse due to high nutrients content of silt and sediment • Smothering of aquatic and marine flora and fauna: high turbidity in Off-site rivers excluding light penetration affects fish life. • Land degradation caused by gully erosion/sediment deposition • Increased pollution of river and streams • Loss of navigable reaches of a river or watercourse • Adverse ecology effects on high sediment loads, deposition and dredging and de-silting of waterways • Decline or total loss of fishing industry, particularly as a results of increased turbidity due to sediment load
The total amount of sediment in the water is called total suspended solids (TSS). When TSS in water occurs in large quantities, degraded water quality can be harmful to animals and plants (Fifield, 2008).
1.2 Study area
This study site comprises of 3 lots (Lot 11897, 11898 and 12025, Mk.12. DBD) of land at
Sungai Ara in Penang state, Malaysia, with a total area of 103.572 acres. The project site is located in the southern end of South-West District on Penang Island and is situated adjacent to Bayan Lepas Town as shown in Figure 1.4. The site is about 2 km away from Bayan
Lepas Town, 3.5 km from Sungai Ara and approximately 5 km from Bayan Baru’s town hub. As the project site was previously a golf course, large portions of the site is covered with secondary vegetation such as trees, shrubs and golf’s course grasses. Rocks and boulders could be found in few locations in the project area. Areas toward the north and west of the site consist of several hills namely Bukit Gambir and Bukit Papan which form the main catchments for Sungai Air Terjun and Sungai Bayan Lepas.
11 In view of the pressing need on housing, this project proponent has taken some necessary steps to alleviate the problem by developing a large scale housing scheme in Sungai Ara which is close to Bayan Lepas Industrial Estate and Bayan Baru Town.
Figure 1.4: Location map of the study area
1.2.1 Rational for Selection of Study Area
This study area is located at hilly land categorized as hill land development in Penang. As reported in the Geotechnical Report (2006), the suitability of the Land with respect to the
12 proposed development area taking into account the site geology, terrain condition and the terrain component was assessed as shown in the table 1.7.
Table 1.7: Landuse Suitability at the study area (Geotechnical Report, 2006)
Land use Suitability Area (m2) Percent (%) Class I (0 – 15°) 301,703.5 74.56 Class II (16° - 25°) 54,932.9 13.57 Class III (26° - 35°) 31,584.9 7.81 Class IV (> 36 °) 16,448.7 4.06
As this is a big scale of hillslope development, (i.e. sensitive area to erosion and sedimentation) which is under rapid construction activities, this area was selected for this researched. During heavy rainfall, high velocity of surface runoff will caused more erosion activities especially on the slope surface. Running water removes soil and organic matter from gentle sloping land and steeper sites by a variety of processes which often starts off as splash erosion, leading to sheet erosion and as the conditions change this will lead to rill erosion and subsequently develop gullies. The eroded particles will be transported and settled at downstream which will lead to siltation and sedimentation. Thus, the depth of the river and drainage system will be shallower which subsequently reduces the capacity of the system and caused flooding. Besides, the eroded particle will also pollute the water quality of the river. On the other hand, the uncontrolled removal of vegetations at the study area has lead to reduction of the infiltration capacity since the surface runoff is force to flow downstream due to the bare surface.
1.3 Problem statement
Sungai Ara has been selected as the research area for its rapid development for the past 10 years. As a result of massive urbanization, erosion problems can be accelerated by a variety of human activities, including unrestricted development, removal of surface cover and increased imperviousness that increases runoff. Every phase of a construction project has the potential of contributing significant quantities of sediment runoff.
13 With its rapid urbanization, the incremental of public awareness for land development in
Penang is undeniable. People have deep feelings about a place or strongly connect with a community when they are in contact with the environment and with other people. In parallel with the developments related to the quality concept in all sectors, various approaches on various scales can be seen for a solution to quality problems in the urban environment. The public are well educate and demanding on the quality of the environment for better living and lifestyle. They are more concern on the safety measures implemented in all the land development in order to avoid any hazardous event. Besides, the State Government has fear on the safety of this development by trying to enforce more guidelines and implementing additional engineering studies especially for hill slope projects such as Geotechnical Report for Hill Land Committee approval, Environmental Impact Assessment (EIA) Report,
Environmental Management Plan (EMP), Erosion Sediments Control Practices (ESCP) report, Traffic Impact Assessment (TIA) report, and others.
For this study area, land development which involves massive construction activities and shaping of this land will definitely alter the land cover and the soil in many ways. These alterations often detrimentally affect on site stormwater patterns and eventually off-site stream and streamflow characteristics. Protective vegetation is reduced and removed during the earthworks activities, excavations are made, topography is altered, the removed soil material is stockpiled and often without protective cover and the physical properties of the soil itself are changed. While rainfall patterns may or may not have been affected by human activities, it is clear that runoff has changed significantly with human development shown in
Figure 1.5.
14 Figure 1.5: Artist illustrations on land development impact on soil erosion Source: Connecticut Guidelines for Soil Erosion and Sediment Control, 2002
While all lands erode, not all land can be the source of sediments pollution. There has always been naturally occurring erosion. However, major problems can occur when large amounts of sediment enter our wetlands, watercourses and drain systems. On developing land, erosion frequently is in the form of gully erosion on land disturbed for a year or less. Both conditions result in lower quality of soil and water resources. However, gully erosion which is the result of concentrated flows of surface runoff generates high sediment volumes requiring costly clean-up and continual need for site stabilization during development. A construction is typically erodes at a rate of 50 tons/acre/year. This erosion rate is five times greater than cropland erosion and 250 times greater than woodland erosion (Connecticut Guidelines for
Soil Erosion and Sediment Control, 2002).
15 Plate 1.1: Typical example of Soil Erosion features on construction site
Uncontrolled erosion and sediment from urban development often cause considerable economic damage to individuals and to surrounding society in general. Improperly planned and maintained land management of the construction site causes continual erosion and sedimentation problem, both during and after construction. The excess runoff from this construction site can cause erosion to the adjacent areas.
On the other hand, the main on-site impact is the reduction in soil quality which results from the loss of the nutrient rich upper layers of the soil and the reduced water holding capacity of many eroded soils. In addition to its on site effects, the soil that is detached by accelerated water erosion may be transported at a considerable distances. Hence, increased downstream flooding and local damage to property may also occur due to the reduced capacity of eroded soil to absorb water.
16 While we strive to improve the quality of our lives, the fact that much of human activities results in damage to the environment comes as no surprise to many of us living in or near to the City. We take on the responsibility of attempting to control and reduce the amount of damage as a society inflict on our water, air, and land. The activity at hand is construction and the damage to focus on in our discussion is the pollution construction contributes to stormwater.
The knowledge of the potential erosion problems on a construction site will enable the site planner to better manage site development and erosion controls in order to minimize soil loss off the property. Prevention is much more effective than trying to improve water quality of the runoff. Therefore, this research is a necessity in order to carry out a study on the efficiencies of the site temporary works and Best Management Practices (BMPs) that has been implemented in order to control the negative impact cause from the study area.
1.4 Objectives
The primary objectives of the study are as follow:
1. To evaluate the soil erosion occurring at the study area during the pre-construction
activities by using the empirical modeling.
2. To compare various equations used by researchers for estimating soil erosion (e.g.
Modified Soil Loss Equation (MSLE), Revised Universal Soil Loss Equation
(RUSLE) and Modified Universal Soil Loss Equations (MUSLE)).
3. To determine the efficiencies of the silt/sedimentation pond as the Erosion and
Sediment Control Practices (ESCP) implemented for this Project.
17 1.5 Research Significance
This work will help in the analysis and assessment of the environmental quality of natural resources and can assist as a future guideline for land use planning in the study area. The result of spatial change detection results and other related findings in this work will helped to identify the main soil erosion process that takes place in the study area.
The various hypothesis considered are as follows;
i. The degree of deterioration of the environment quality is not uniform throughout
the study area.
ii. The natural influences are determining factors for the soil erosion process in the
study area.
iii. Revised Universal Soil Loss Equation (RUSLE), MUSLE and MSLE equations
may be helpful in evaluating the soil loss.
iv. The Soil investigation reports may be helpful in the estimating the K factor (soil
erodibility factor).
v. The Geotechnical and Environmental Impact Assessment (EIA) reports may be
useful for the determination of slope length and gradient and also the land cover
factor.
1.6 Research Report Outline
This research report is organized in six (6) chapters followed by sections and subsection as follows:
i. Chapter One briefly introduces the research, a short description of the study area
with respect to its location including objectives and scope of works of the study.
ii. Chapter Two contains literature review of relevant studies regarding to data
collection, soil erosion, modeling and etc.
iii. In Chapter Three, Materials, Research Methods and Techniques are discussed
together with site description including its location, climate, hydrology and geology.
18 iv. Chapter Four contains the overall result for data analysis and its discussion includes
the general description of soil erosion models using MSLE, RUSLE and MUSLE
equations.
v. Chapter Five is the further discussion on the results obtained from data analysis; and
vi. Chapter Six is the conclusion and recommendations for this research.
The summary showing the research work flow is illustrated in Figure 1.6.
No
Yes
Figure 1.6: The research work flow
19 CHAPTER 2
LITERATURE REVIEW
2.0 Introduction
Erosion can be a major environmental problem worldwide as shown in Plate 2.1. It can affect the land and its inhabitants either in direct or indirect ways. Soil erosion is an issue where the adage “think globally, act locally,” is clearly apropos. Think globally as soil erosion is a common problem that will always continue to impact the global community. Act locally since effective erosion control requires action at the hill slope, field, stream channel and upland watershed scales (Toy et. al., 2001).
Plate 2.1: Soil erosion phenomena on bare slope
20 2.1 Definition of Soil Erosion
The word "erosion" is derived from the Latin "erosio", meaning "to gnaw away". In general terms soil erosion implies the physical removal of topsoil by various agents, including rain, water flowing over and through the soil profile, wind, ice or gravitational pull (University of
Hong Kong, 2000).
Erosion is the process of carrying away or displacement of sediment by the action of wind, water, gravity, or ice (Smith and Smith, 1998). The process of deposition of sediment from a state of suspension or solution in a fluid is called sedimentation. Natural sources of sediments transported to the sea include erosion of bedrock, soil and decomposition of plants and animals (United Nation Environment Programme and Gems Water Programme
[UNEP/GPA], 2006). However, anthropogenic activities or those which are carried out by man often change the processes of erosion and sedimentation as well as modifying the flow of rivers and the amount of sediments it can carry. Most land based activities that occur in sectors such as agriculture, forestry, urbanization and mining contribute to these changes.
Another significant cause of changes in sedimentation and erosion patterns is through hydrological modifications that may occur from construction of reservoirs, dams and causeways, dredging of water bodies and development of large scale irrigation schemes
(UNEP/GPA, 2006a).
Al-Kaisi (2002) stressed that soil erosion is a gradual process that occurs when the impact of water or wind detaches and removes soil particles causing the soil to deteriorate. According to Al-Kaisi, soil deterioration and low water quality due to erosion and surface runoff have become severe problems worldwide.
Soil erosion events are quick processes (Blaikie and Brookfield, 1987; Lal, 1990; and Eaton
1996) and can be defined as a physical process. It refers to the wearing away of land surface
21 by water or wind as well as to the reduction in soil productivity due to physical loss of topsoil, reduction in rooting depth, removal of plant nutrients and loss of water.
It is particularly problematic in tropical countries because of high rainfall intensities and generally less fertile soil. It is also a threat to those developing countries when agriculture production is crucial to development and the majority of the rural population base livelihood strategies on the primary sector. Unfortunately, many of such rural residents have been pushed to the margins of agricultural production, i.e. shallower and poorer soils, and the sloping land and forest frontiers of the uplands. In this situation, agriculture can be the main cause of soil erosion and watershed deterioration, though the impacts of other activities such as road construction or logging operation should not be downplayed. Cultivating upland soils often lead to a reduction in natural soil fertility and crop productivity thus undermining future income generation (Alfsen et al., 1996) and economic growth (Alfsen et al., 1997).
Soil erosion and the depletion of soil resources have an important economic implications for countries whose economic depend heavily on the agricultural sector (Barbier and Bishope,
1995).
Adapted from Maine Department of Transportation (MaineDOT) BMPs for Erosion
Sediment Control (ESCP) Manual (2008), erosion is the detachment and movement of soil particles by the action of water, ice, gravity, or wind. Natural erosion always occurs but the rate is slow enough that the environment can adjust. When humans began to manipulate the landscape, it will accelerate the process by exposing soil to the forces of water and wind. On the other hand, sedimentation is the deposition of soil particles that were detached and transported by the erosion process. Sedimentation occurs when the velocity of the wind or water becomes insufficient to keep the soil particles in suspension. Particles can be transported at great distances and deposited in environmentally sensitive areas such as rivers, lakes and wetlands. It is sedimentation that can severely alter water quality, damage an aquatic ecosystem and destroy a wetland.
22 According to Mortlock (2007) soil is naturally removed by the action of water or wind. Soil erosion has been occurring for some 450 million years ago since the first land plants formed the first soil. In general, erosion removes soil at roughly the same rate as soil is formed. But
'accelerated' soil erosion (loss of soil at a much faster rate than it is formed), is a far more recent problem. It is always a result of mankind's unwise actions that leave the land unprotected and vulnerable during times of erosive rainfall or windstorms where soils may be detached, transported, and deposited.
The Global Assessment of Human Induced Soil Degradation (GLASOD) (1987-1990) study as shown in Figure 2.1 estimated that around 15% of the Earth's ice free land surface is afflicted by all forms of land degradation. From this, accelerated soil erosion by water is responsible for about 56% and wind erosion for about 28%. This means that the area affected by water erosion is roughly around 11 million square km and the area affected by wind erosion is about 5.5 million square km (Mortlock, 2007).
Figure 2.1: The GLASOD estimate of global land degradation (Note that this includes all forms of soil degradation, not just erosion) Source: UNEP (World Atlas of Desertification) GRID (Mortlock, 2007)
The consequences of soil erosion can be seen both on site and off site. On site effects are the loss of soil, the breakdown of the soil structure and a decline in organic matter. Erosion also reduces available soil moisture, resulting in more draught-prone conditions. Off site
23 problems result from sedimentation downstream or downwind which reduces the capacity of rivers and drainage ditches, increases the risk of flooding, blocks irrigation canals and shortens the design life of reservoirs. Eroded sediment is also a pollutant which the chemicals absorbed by it can increase the levels of nitrogen and phosphorus in water bodies and result in eutrophication (University of Hong Kong, 2000).
2.1.1 Why does erosion occur?
Erosion is very much depends on the power balance between the rainfall and the soil. Rain and its runoff provide the force to drive water erosion. If the force applied to the soil is greater than the resistance of the soil, then particles will detach and move away in either splash or in surface flows. As the force increases so does the rate of detachment. This gives the first clue to keeping erosion down to acceptable limits. We can do very little about reducing the force applied by the rain but we can work at dissipating its energy before it reaches the soil surface (Cummings, 1998).
2.1.2 How does erosion occurs
Detachment, transport and deposition are basic processes that occur on upland areas (Foster,
1982). Detachment occurs when the erosive forces of rainfall drop impact or when flowing water exceeds the soil's resistance to erosion. Detached particles are transported by the splash and flow of raindrop. Deposition occurs when the sediment load of eroded particles exceeds its corresponding transport capacity and generally will be transported down slope flowing into rills and gullies as shown in Figure 2.2. Understanding the soil erosion mechanism is very important to design the soil erosion measurement system and develop the soil erosion control techniques (Choi et al., 2005).
24