The aim of this research is to assess the existing storm water drainage and management in Yenagoa, with the view to suggest relevant measures for ameliorating the condition. The objectives of the study include (a) assessing the problems and challenges of storm water, (b) climatic and hydrological settings of the study area, and (c) develop an effective management strategy to mitigate the problem. The research adopted a multi-stage sampling procedure to select 6 communities in the study area. Simple random sampling technique was used to determine the sample size from the selected communities and 377 questionnaires were administered to the respondents and key informants in the study area. The Spearman Rank Correlation Analysis was used to test the relationship between the adequacy of drains and annual flooding incidence in the study area.
The research found that lack of storm water management in the study area and extensive urban development especially on wetlands due to pressure of urbanisation; poor development control mechanisms had caused flooding incidents in the study area. The study recommends that the Yenagoa Master, 2004 should be implemented and proffers a Model of Urban Stormwater Improvement Conceptualisation. The study also recommends that the Bayelsa State Physical Planning Board should prepare and enforce development control regulations that recognize the poor drainage system that currently exists. Efforts should be made to keep the natural drainage paths and wetlands clear with adequate storm water infrastructure provided.
TABLE OF CONTENTS
Abstract
Declaration
Certification
Acknowledgement
Dedication
Table of Contents
List of Tables
List of Figures
List of Plates
List of Appendices
List of Abbreviations
CHAPTER 1: INDRODUCTION
1.1 Background to the Study
1.2 Statement of the Problem
1.3 Aim of the Study
1.3.1 Objectives of the Study
1.4 Research Questions
1.5 Research Hypothesis
1.6 Significant of the Study
1.7 Scope of the Study
1.8 Description of the Study Area
1.9 Limitation of the Study
1.10 Definition of Terms
CHAPTER 2: LITERATURE REVIEW
2.1 Technologies for Storm Water Management in Urban Areas
2.1.1 Retention Ponds
2.1.2 On-site Detention (OSD)
2.1.3 Rainwater Harvesting
2.1.4 Green Roofs
2.1.5 Constructed Wetlands
2.1.6 Infiltration Trenches
2.1.7 Grass Filter Stripes
2.1.8 Grassed Swales
2.1.9 Pervious Pavements
2.1.10 Infiltration Basin
2.2 Strategies in Urban Flood Management
2.2.1 Hard Engineering Techniques
2.2.1.1 Dams
2.2.1.2 Artificial Levees
2.2.1.3 Wing Dykes
2.2.1.4 Channel Straightening
2.2.1.5 Diversion Spillways
2.2.2 Soft Engineering Techniques
2.2.2.1 Flooding Zoning
2.2.2.2 Afforestation
2.2.2.3 Wetland Restoration
2.2.2.4 River Restoration
2.3 Problems of Urban Flooding
2.3.1 Economic
2.3.2 Environment
2.3.3 People, Animals and Plants
2.4 Effects of Climate and Hydrological Factors on Storm Water Management
2.5 Effects of Landuse on Urban Flooding
2.6 Other Causal Factors of Flooding
2.7 Problems and Challenges of Urban Flood Management
2.8 Storm Water Management in some Countries
2.8.1 United States of America
2.8.2 South Africa
2.9 Policy and Legislation of Storm Water Management in Yenagoa
2.10 Summary of Literature Review and Identification of Research Gaps
CHAPTER 3: METHODOLOGY
3.1 Introduction
3.2 Research Design
3.3 Sources of Data
3.3.1 Primary Sources
3.3.2 Secondary Sources
3.4 Population and Sampling
3.4.1 Sampling
3.4.2 Sample Size
3.5 Instrumentation and Data Collection
3.6 Description of Statistics and Data Analysis
3.6.1 Analytical Techniques for Data Analysis
3.7 Validity and Reliability of the Instruments
CHAPTER 4: DATA PRESENTATION AND ANALYSIS 52
4.1 Introduction
4.2 Data Presentation and Analysis
4.2.1 Personal Characteristics of Respondents
4.2.1.1 Sex of Respondents
4.2.1.2 Marital Status of Respondents
4.2.1.3 Educational Status of Respondents
4.2.1.4 Employment Status of Respondents
4.2.1.5 Occupation of Respondents
4.2.2 Flood Problems and Challenges in the Study Area
4.2.2.1 Drainage Facility Provided in the Street and Functionality
4.1.2.2 Adequacy of Drainage
4.2.2.3 Communities and Strom Water Infrastructure Availability and Condition
4.2.2.4 Challenges of Inadequacy of Drainage in the Study Area
4.2.2.5 Reasons for Poor Functional Drainage in the Community
4.2.2.6 Effects of No Drainage in Street and Community
4.2.2.7 Experiencing Flooding in the Community
4.2.2.8 How Often Flooding Incidence is Experienced in the Community
4.2.2.9 Effects of Flooding in the Community
4.2.2.10 Assessment of Government Performance in Storm Water Management in the City
4.3 Climatic and Hydrological Data Presentation and Analysis
4.3.1 Climatic Settings of the Study Area
4.3.1.1 Monthly Average Rainfall Distribution of the Study Area
4.3.1.2 Monthly Average Temperature Distribution of the Study Area
4.3.2 Hydrological Settings of the Study Area
4.3.2.1 Hydrological and Development Characteristics of the Study Area
4.3.2.2 Topography of the Study Area
4.3.2.3 Natural Drainage Flow and Accumulation Systems of the Study Area
4.4 Extent of Urbanisation in the Study Area
4.5 Other Factor Exacerbating Flooding in the Study Area
4.6 Testing of Hypothesis
CHAPTER 5: INTERPRETATION AND DISCUSSION OF FINDINGS 88
5.1 Introduction
5.2 Flood Problems and Challenges in the Study Area
5.3 Climatic and Hydrological Conditions of the Study Area
5.4 Dynamics of Landuse Pattern of the Study Area
5.5 Other Factors Contributing to Storm Water Management in the Study Area
5.6 Perception of the Residents on Storm Water Management in the Study Area
5.7 Physical Planning Issues
5.8 Solutions for Effective Storm Water Management in the Study Area
CHAPTER 6: CONCLUSION AND RECOMMENDATIONS
6.1 Introduction
6.2 Conclusion
6.3 Recommendations
REFERENCES
APPENDICES
ABSTRACT
Yenagoa, capital city of Bayelsa State, lies in floodplain and surrounded by freshwater swamp environment of the Nun River, Ekole and Epie Creeks, lakes and other natural drainage paths. The city is annually inundated for about nine months in every year. The causal factor of this flooding is primarily high and continuous rainfall during the year. The aim of this research is to assess the existing storm water drainage and management in Yenagoa, with the view to suggest relevant measures for ameliorating the condition. The objectives of the study include (a) assessing the problems and challenges of storm water, (b) climatic and hydrological settings of the study area, and (c) develop an effective management strategy to mitigate the problem. The research adopted a multi-stage sampling procedure to select 6 communities in the study area. Simple random sampling technique was used to determine the sample size from the selected communities and 377 questionnaires were administered to the respondents and key informants in the study area. The Spearman Rank Correlation Analysis was used to test the relationship between the adequacy of drains and annual flooding incidence in the study area . The research found that lack of storm water management in the study area and extensive urban development especially on wetlands due to pressure of urbanisation; poor development control mechanisms had caused flooding incidents in the study area . The study recommends that the Yenagoa Master, 2004 should be implemented and proffers a Model of Urban Stormwater Improvement Conceptualisation. The study also recommends that the Bayelsa State Physical Planning Board should prepare and enforce development control regulations that recognize the poor drainage system that currently exists. Efforts should be made to keep the natural drainage paths and wetlands clear with adequate storm water infrastructure provided.
DECLARATION
I, EYENGHE Tari (PG.2014/00453), declared the work in this dissertation represent my original work and have not been previously submitted elsewhere or in this University for the award of a degree.
Signature:
Date:
CERTIFICATION
We the undersigned, certify that this work was carried out by EYENGHE, Tari (PG.2014/00453) under the supervision of Professor Essaghah Aurthur and Dr. Igwe Chimezie Franklin in the Department of Urban and Regional Planning, Faculty of Environmental Sciences, Rivers State University, Nkpolu-Oroworukwo, Port Harcourt has met the partial requirement for the award of Master of Science degree in Urban and Regional Planning.
Name:
Chairman, Supervisory Committee
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Signature & Date:
Member, Supervisory Committee
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Signature & Date:
Head of Department
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Signature & Date:
Dean of Faculty
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External Examiner
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ACKNOWLEDGEMENT
In carrying out this research it was challenging and rewarded by experience to me, though, it would not have been successful without the assistance of some persons. Therefore, I wish to express my profound gratitude to the Almighty God who gave me the grace and mercies to carry out this research. I also, thank my wife and son; Mrs. Comfort Tari and Davis Eyenghe for their support, encouragement and patience during this period and also my parents; Mr. and Mrs. Maclean K. Eyenghe and siblings; Ndolayefa, Alaere, Peretimi, Sunny, Ebiowei, Diepreye and Idisenimi for their prayers, supports and understanding. My indebtedness goes to my supervisors Prof. Essaghah, Arthur and Dr. Igwe, Chimezie Franklin for their patience and direction. Thank you sirs.
My deepest appreciation goes to all my lecturers and classmates in the department but to mention few; Prof O.B. Owei and Ms. Jane Emeruem who played motherly role throughout my study, Prof. T.S.K. Abam, Tpl. Dike Emmanuel, Tpl. Ibama Brown, Mr. Visigah Nekabari, Tpl Johnbull S., Akue Leka-Oscar and Tpl Visigah Kpobari for their supports. I also want to appreciate Tpl. Tarimobowei Ikposo, Tpl. (Mrs.) Wocha Chikagbum, Tpl. Ene Marcus, Tpl. (Mrs.) Stella Enyadike, Tpl. Eleeh Chimezie, Sir Abiye Abere, Comr. Johnson Wakama and Rev. Canon Vincent B. Igu for their inspirations and encouragements.
I must not fail to appreciate and be grateful to all contributors to the success of this work including Akor Victor, Ogolo Idagogo, Mr. Justice, Mr. Lawan and others that are not mentioned because of time and space, the Almighty God will continue to bless you and grant you your hearts desires in Jesus name, Amen.
DEDICATION
This work is dedicated to my Wife and Son; Comfort and Davis
LIST OF TABLES
3.1 Determination of Sample Size for the Study
4.1 Educational Status of Respondents
4.2 Occupation of Respondents
4.3 Communities and Storm Water Infrastructure Condition
4.4 Reasons for Poor Functional Drainage in the Community
4.5 Assessment of Government Performance in Storm Water Management in the City
4.6 Monthly Average Rainfall Distribution of Yenagoa City (2006-2015)
4.7 Monthly Average Temperature Distribution of Yenagoa City (2006-2015)
4.8 Hydrological Settings and Development Characteristics of the Study Area
4.9 Extent of Urban Growth and Development of the Study Area at 2010
4.10 Extent of Urban Growth and Development of the Study Area at 2016
4.11 Spearman Correlation Analysis on the Relationship between Adequacy of Drains and Annual Flooding Incidence in the Study Area
LIST OF FIGURES
1.1 Map of Bayelsa State Showing Yenagoa City LGA
1.2 Map of Yenagoa City LGA Showing the Study Area
4.1 Sex of Respondents
4.2 Marital Status of Respondents
4.3 Employment Status of Respondents
4.4 Drainage Facility Provided in the Street
4.5 If yes, is the Drainage Functional
4.6 Adequacy of Drainage System
4.7 Economic Challenge
4.8 Social Challenge
4.9 Health Challenge
4.10 Environmental Challenge
4.11 Economic Effect
4.12 Social Effect
4.13 Health Effect
4.14 Environmental Effect
4.15 Experiencing Flooding in the Communities
4.16 How Often Flooding Incidence is Experienced in the Communities
4.17 Economic Effect
4.18 Social Effect
4.19 Environmental Effect
4.20 Monthly Average Rainfall Distribution of Yenagoa City
4.21 Monthly Average Temperature Distribution of Yenagoa City
4.22 Hydrological Settings and Development Characteristics of the Study Area
4.23 Topographic Map of the Study Area
4.24: 3D Topographic Model of the Study Area
4.25 Natural Drainage Paths Flow Direction and Accumulation Patterns of the Study Area
4.26 Extent of Urban Growth and Development of the Study Area at 2010
4.27 Extent of Urban Growth and Development of the Study Area at 2016
6.1 Proposed Sustainable Storm Water Management Framework for the Study Area
LIST OF PLATES
5.1 A Section of a Natural Drainage System at Amarata Community Clogged-up with Water Hyacinths and Wastes
5.2 Wetland Occupied by Residential Buildings at Swali
5.3 An Environmental Sensitive Area (Wetland) not Properly Planned Earmarked as Central Business District at Swali
5.4 Unplanned Residential Neighbourhood within a Floodplain Area with a Wood Footpath “Monkey Bridge” to Access Buildings
5.5 Isaac Adaka Boro Road one of the Major Road in the Study Area without Drainage
5.6 Open Drainage System along Amb. Otioto Street that is not Functional
5.7 A Street in Biogbolo Community without Drainage System Overtaken by Grasses
5.8 A Street with a Non-Functional Drainage System
5.9 A Natural Drainage System at Biogbolo Community that is Stagnant with Wastes not Flowing Causing Environmental and Health Problems
5.10 A Street in Amarata Community with Blocked Drainage System
5.11 A Self-Help Drainage System Dug by Residence of Biogbolo Community
5.12 The Amarata Creek Connecting Epie Creek
LIST OF APPENDICES
1 Proposed Sustainable Storm Water Management Framework for the Study Area
2 Household Questionnaire
3 Key Informant Questionnaire
4 Soil Profile for the Study Area
5 Statistical Package for the Social Sciences (SPSS) Result for Spearman Rank
LIST OF ABBREVIATIONS
AHTD Arkansas State Highway and Transport Department
CBD Central Business District
CoCT City of Cape Town
CoJ City of Johannesburg
CoT City of Tshwane
CRC Current Replacement Cost
CSIR Council for Scientific and Industrial Research
CVC CVC Capital Partners
CZM Coastal Zone Management (Massachusetts)
DEP Department of Environmental Protection (Massachusetts)
DRC Depreciated Replacement Cost
ESTs Environmentally Sound Technologies
FINS Flood Information and Notification System
HEC-1 Hydrologic Engineering Centre 1
HEC-RAS Hydrologic Engineering Centre – River Analysis System
IUWM Integrated Urban Water Management
LAO Legislative Analysis’s Office (California)
LuMS Landuse Management System
NAS National Academy of Science (US)
MDAs Ministries, Departments and Agencies
NEMA National Emergency Management Agency
NIMET Nigeria Meteorological Agency
NJDEP New Jersey Department of Environmental Protection
NRC National Research Council
NWS National Weather Service
O&M Operation and Maintenance
OSD On-site Stormwater Detention
StormwaterPA Pennsylvania Stormwater Management
SuDS Sustainable Drainage Systems
TRCA Toronto Region Conservation Authority
UNEP United Nations Environment Programme
UPRCT Upper Parramatta Catchment Trust
USEPA United States Environmental Protection Agency
USGS United States Geological Survey
UWC Urban Water Cycle
CHAPTER 1
INTRODUCTION
1.1 Background to the Study
Globally the rate of loss and damage that are disaster related either anthropological or natural is alarming resulting in great economic loss and loss of millions of lives for the past three decades. Urban areas, where about one half of human population are presently residing and most of the world’s human-made developments are concentrated are fast becoming the focal point for natural and human-induced disasters which have caused devastating destruction and losses (UN-HABITAT, 2007). However, rapid urbanization, coupled with global environmental changes, as a result of climate change and heavy human activities has resulted increased vulnerable or exposed areas (disaster hotspots) presently serving as human settlements (UN-HABITAT, 2007).
UN-HABITAT (2007) defined disaster as a situation where the resilience of the people is overwhelmed. These natural or human-induced disasters include; landslides, mudslides, flooding, droughts, earthquakes, tsunamis, volcanoes, avalanches, ecological damage, fire, etc. Though, the spotlight of this research is the assessment of storm water management and problems which cause pluvial flooding and environmental degradation in settlements especially in urban areas, and the strategy for effective storm water management in Yenagoa City.
The management of storm water is a significant challenge in several urban areas in Nigeria. Urban areas often times have local flooding as storm water is channelled along streets as runoff may not be able to escape from the environment and may cause flooding (Bryan 2002). Thus, the period of heavy rains is known in Nigerian cities for flooding and associated damages. This human-induced disaster is a major problem and concern to the global communities, especially in urban areas, whose surface has grossly been paved and concretized through urban development. This has considerably caused environmental, social, health and economic problems in the built environment whether in developed or developing societies (Enger et al., 2006) but more commonly in developing societies. In the past, many developed cities had single system to handle both sewage and storm water runoff, which during heavy precipitation, the runoff from streets could be so large for waste water treatment plants to handle the volume and these waters will be directed to any natural water bodies close without treatment. Currently the developed cities have separated sewage and storm water runoff for easy treatment and handling (Enger et al., 2006).
The Encarta Dictionary (2009) defines storm water as the water channelled into a constructed or natural drain large enough to contain excess water overflowing the surface. Storm water is also defined as water that runs off streets and buildings and is often added directly to the sewer system and sent to the municipal wastewater treatment facility (Enger et al., 2006). In the environment storm water can infiltrate into the soil, also held on the surface of the earth and evaporate, or overflow and emptied in nearby streams, rivers, or water bodies in the environment.
Natural landscapes such as forests and grasslands, the soil absorbs much of the storm water and plants hold storm water close to where it discharges. In built-up environments, unmanaged storm water can cause two major problems namely flooding and the other related to potential contaminations from pollutants that the runoff is carrying (water pollution) (Schueler, 2000; Alex and Robert, 2005). Storm water is also a resource and important as the world’s human population water demand exceeds readily available water for use as a result of rapid population growth especially in urban areas where most of the world population is concentrated. The sustainable technique which is appropriate for storm water harvesting is from point source, water management and purification (treatment) this can make urban environments to be self-sustaining in terms of water resources. Storm water has been shown to be one of the leading contributors to pollution of urban waterways since it can contain fertilizers, oil, pesticides, trash, sediment and animal wastes from human activities. Therefore, because of this condition, certain storm water discharges are regulated by Environmental Protection Agencies (EPAs) in developed countries (AHTD, 2015).
The rapid increase in occurrence and intensity of extreme rainfall events has been high in recent decades and it is evident also that both the frequency and intensity of floods have increased (Temi and Durowoju, 2014).In the wake of increased human developmental activities, runoff increases resulting in poor quality of surface and ground water resulting in growing concern on the handling methodology of treating and monitoring storm water and ensuring better quality of surface and ground water as a result of storm water through engineering solution (Bryan, 2000).
Environmental hazards attributed to water related hazards resulting from improper storm water management characterize coastal environments and Nigeria is not an exception. The Niger Delta region, which is a coastal region and a floodplain experiences storm water management challenges especially in the cities located in this region as they are convergent point for population. However, the increase in population and human reckless interference with the environment in the quest for industrialization, agriculture, urbanization and settlement development, etc have in addition to this geo-hazard resulted in serious ecological and socio-economic problems (Oyeleke, 2014).
In Niger Delta region, Yenagoa City, which lies within floodplain, is developing rapidly without proper landuse management and urban planning. The City suffers regular flooding, environmental consequences and socio-economic challenges due to lack of adequate storm water management system. Hence, the city, which experiences high precipitation, periodic inundation of the Ekole and Epie Creeks, high water table with poor soil draining capacity, and poor drainage system has increased flooding (Yenagoa Master Plan, 2004).
The poor drainage system in Yenagoa has caused environmental, social, health and economic problems to government and the residents of the city. The question that arises is how to mitigate the poor storm water management and planning from causing regular pluvial flooding and the resultant environmental problems faced by inhabitants of the city.
Thus, the patterns of precipitation variability in the various regions of the earth have also triggered urban flooding especially in the deltaic environment (Fellmann et al., 2005). Uncontrolled and poorly managed urbanization and urban system in Nigeria has given rise to storm water problems causing regular flooding in urban centres that are located in the coastal regions of the country and Yenagoa City is not an exception. The concern of this research is how to provide an effective and efficient storm water management system to control and manage this unsustainable environmental problem in the city using proactive measures by government and professionals in the built environment using best practice physical planning techniques and skills.
1.2 Statement of the Problem
A lot of studies have been carried out on Yenagoa City by government and individuals concerning storm water management and flooding challenges it has caused but none of the studies have provided effective strategy for storm water management in the city (Yenagoa Master Plan, (2004) and Yenagoa City Development Strategy (2007). If the city flooding remains unchecked challenges such as environmental degradation (erosion and biodiversity loss), public health issues (pollution and contamination of surface and underground water), and socio-economic issues (loss of lives, distortion of livelihoods and properties and displacement of people) will be exacerbated.
Therefore, there is an urgent need to address this urban menace. Hence, this study intends to assess the storm water management system of Yenagoa City and proffer a workable and appropriate strategy for effective storm water management in the city.
1.3 Aim of the Study
The aim of this research is to assess the existing storm water drainage and management in Yenagoa, with the view to suggest relevant measures for ameliorating the condition.
1.3.1 Objectives of the Study
To achieve the aim of the study, the objectives of the study are to:
i. Examine the existing storm water problems and challenges in Yenagoa City;
ii. Examine the climatic and hydrological setting of Yenagoa City;
iii. Identify factors that lead to inadequate storm water management and incidence of flooding in the city; and
iv. Develop an effective storm water management frame work for Yenagoa City.
1.4 Research Questions
The research questions are:
i. What are the problems and challenges associated with storm water management in the study area?
ii. To what extent does the existing climatic and hydrological characteristic of the study area affect storm water management in the city?
iii. What are the factors responsible for inadequate storm water management and incidence of flooding in the study area?
iv. How can an effective strategy to manage storm water in Yenagoa City be developed?
1.5 Research Hypothesis
The research hypothesis below was tested:
[Ho] There is no significant relationship between adequacy of drains and annual flooding incidence in the study area.
1.6 Significance of the Study
The significance of this study cannot be overemphasized. This study has both theoretical and practical implications. Theoretically, the study is contextualized as an inter-disciplinary study of planning in relation to storm water management, urban development strategies and planning in Yenagoa City. This research is established upon the identification of the gap between planning and urban management specifically storm water management and in relation to city development, specifically planning approaches, policy formulation and implementation, stakeholder interactions in environmental management and planning. Findings from the study will add perspectives to existing discussions in the literature on storm water management in a coastal or deltaic city. Hence, the study will contribute to the discussions on urban planning and storm water management practice. Practically, the research results in policy recommendations for improvement of storm water management in Yenagoa City to mitigate the negative effects of flooding in the city and to achieve a sustainable urban system.
1.7 Scope of the Study
The geographical scope of this study covers selected communities in Yenagoa City Local Government Area. The parameters to be measured in the study include the climatic and hydrological characteristics of the study area; patterns of landuses and their growth direction in the study area; the main causes of inadequate storm water management system in the study area as well as the factors inducing flood related problems and challenges (see Fig. 1.1 and Fig. 1.2).
Abbildung in dieser Leseprobe nicht enthalten
Fig. 1.1: Map of Bayelsa State Showing Yenagoa City LGA
Source: Surveyor General Office, Bayelsa State, 2016
Abbildung in dieser Leseprobe nicht enthalten
Fig. 1.2: Map of Yenagoa City LGA Showing the Study Area
Source: Surveyor General Office, Bayelsa State, 2016
1.8 Description of the Study Area
Yenagoa City is the administrative capital of Bayelsa State and the emerging centre of business and economic activities in the Niger Delta region of Nigeria. Yenagoa City is the core of the state and also having oil and gas resources within her confines. The city territorial boundaries lies on latitude 4o55 N and longitude 6o16 E in Bayelsa State. The city total spatial areas from the Yenagoa Master Plan of 2004 spread across four (4) LGAs which include Kolokuma-Opokuma, Ogbia, Yenagoa and Southern Ijaw LGAs. This area is designated as the planning area which is about 15km radius (Yenagoa Master Plan, 2004). Yenagoa City is bounded at the north and east by Rivers State, at the south by Southern Ijaw and Ogbia LGAs, and at the west by Kolokuma-Opokuma LGA. Yenagoa covers about 70,700 hectares (176.750 acres) and lying within three (3) rivers courses namely; the Nun River, Ekole and Epie Creeks (Yenagoa Master Plan, 2004).
The city of Yenagoa is crisscrossed and surrounded by river, creeks, lake, back-swamps and ponds which are mostly used as navigation routes such as the Nun River, Ekole and Epie Creeks, Ox-Bow Lake and other back-swamps. The Nun River is a tributary of River Niger is located at the south-west region of the city, the Ekole Creek is a tributary of the Nun River and is located at the southern part of the city and Epie Creek is a tributary of the Ekole Creek that runs from the western part of the city to the north forming a natural levee in the city and the Ox-Bow Lake is located at the southern part of city linking the Ekole Creek. There are vast deltaic swamps of fresh water ecological setting, marshy and wetlands around and within the city which serves of retention ponds for collection of storm water during rainy season (Yenagoa Master Plan, 2004). These natural constraints have a strong bearing on the direction of urban growth and development in the city, though, this is tourism potential for the socio-economic development of the city and state in general as not to rely on oil and gas activities alone. These opportunities have not been fully explored by the government and citizens of the state, even foreign investors have not tapped into these valuable resources.
Yenagoa City is located within the subequatorial south, and the region is extended from the coast to roughly 130 to 160 km inland. The city and its territorial region experiences heavy rainfall for eight to nine months of the year between Aprils to November. The highest means rainfall are 322.92mm (June) 413.59 (July), 438.34 (August) and 439.84 (September) are recorded in the area. The direct effect of the wet season is over 70% of the total area of Bayelsa State which is inundated with fluvial flooding during the wet season. This condition is exacerbated by semi-diurnal tidal regime, which ensures two high tidal floods and two ebb tides within the course of each day all over the coastal areas of the state (Yenagoa Master Plan, 2004).
The highest temperature is normally experienced between the months of February and March each year while the lowest in the year are recorded between the months of June and July. The variation in temperature begins in February which is about 30oC and the lowest is about 26oC in July. The relative humidity is comparatively uniform over the entire state because of the proximity to the Atlantic Ocean (Yenagoa Master Plan, 2004).
Yenagoa City region is uniquely complex in ecological biodiversity and the topography of low-plain and uniquely sitting on wetlands and swamps susceptible to seasonal flooding. The types of soils found within the area are sandy, loamy, clay and peat soils and this depends on the parent material which the soils are formed from. The soils present in the study area are more of clay and sandy which made development efforts cumbersome. However, the environment and soil has low bearing capacities and poorly drained soil.
The population estimates for Bayelsa State is about 1.2 million populations from the 1991 Census Report. According to the 1991 census report, the Yenagoa City area had a population of approximately 50,000 persons. Population extrapolations and projection made in the 2004 Yenagoa Master Plan estimated in 2001 a population of approximately 65,500 persons in the immediate city area and some 200,000 persons within the 15km radius of the entire city (Yenagoa City Development Strategy, 2007).
1.9 Limitation of the Study
Every research comes with challenges. The research is faced with numerous challenges of obtaining accurate and concise information from the study area about the subject matter. One major challenge is the mapping of the rivers, creeks, lakes, back-swamps, ponds in an accurate manner to reveal their hydrological characteristics. There are also challenges identification and characterizing the natural drainage paths due to construction of buildings along these drainage paths. Also, obtaining and projecting rainfall and temperature data for the study area. Urbanisation and landuse data were also difficult to obtained and projected to characterize the landuse pattern and activities of the study area.
1.10 Definition of Terms
Disaster: It is a sudden occurrence of hazardous event that result in the loss of property and lives of communities or society affecting greatly their coping capacity and resilience (Geographypods, 2016).
Drainage: The process of draining liquid from something (Encarta Dictionary, 2009).
Environment: Everything that affects an organism during its lifetime this includes the biophysical, social and health components (Enger, et al, 2006).
Flooding: This is a situation where lands that usually dry are covered by river overflowing or heavy rainfall (Encarta Dictionary, 2009).
Floodplain: Lowland area on either side of a river that periodically covered by water (Enger et al., 2006).
Hazard: Exposure to potential harm that could be caused by proximity to environmental risk (Enger et al., 2006).
Human-Induced Disaster: These are events that were induced by anthropogenic events that could harm mankind resulting in loss of lives and properties (BusinessDictionary, 2016).
Landuse: This is the various uses land is put to e.g. residential, commercial, industrial, recreational, agricultural and administrative (institutional) (Rangwala et al., 2009).
Pluvial Flooding: This occurs when an extremely heavy downpour of rain saturates the urban drainage system and the excess water cannot be absorbed (Josh, 2011).
Runoff: The water that moves across the surface of the land and enter a river system (Enger et al., 2006).
Settlement: A group of people living in a particular place a given time.
Storm Water: Storm water as the water channelled into a large drain built to carry away excess water from a road during heavy rain. (Encarta Dictionary, 2009).
Storm Water Management: This is an activity and facility developed to reduce the amount or quantity of storm water runoff and provide time for most pollutants to settle in a holding area where they will not be transported to streams to improve water quality (Fairfax County, 2016).
Sustainable Development: Using renewable resources in harmony with the ecological systems to produce a rise in real income per person and an improved standard of living for everyone (Enger et al., 2006).
Urban: Relating or having the characteristic of a city (Encarta Dictionary, 2009).
Urban Planning: The planning of the physical and social development of a city through the design of its layout and the provision of services and facilities (Encarta Dictionary, 2009)
CHAPTER 2
LITERATURE REVIEW
2.1 Technologies for Storm Water Management in Urban Areas
Generally, urban growth and development will significantly change, alter, affect or make an impact on the environment. The building of structures, infrastructure and roads has extensively changed the hydraulic properties of many human settlements. Physically, some areas have been identified to be less permeable or even impermeable to storm water and these areas are depressed and raised to check ponding or dishing to trap runoff in the environment. The development of surface and conduit drainages is provided to drain runoff efficiently and sustainably in well planned urban areas and always remove natural vegetation which causes reduction, interception and transpiration of plants in the environment (CSIR, 2000).
These limited vegetations cover in the environment exposes the soil to the impact of rain during precipitation that lead to increased erosion and flooding in the environment. Rationally, the direction of water systems may be canalized to more effectively route flows through the development with the assistance of drainages. Storm water management is the science or skill for limiting negative impacts of storm water on the environment and enhancing the positive impacts or catering for the hydraulic needs of a development in any environment while minimizing the associated negative impacts (CSIR, 2000).
Hence, the impermeable surfaces in urban areas as a result of extensive development, usually encourages flooding frequently as human-induced activity. Runoff from such concretized surfaces has a high velocity in flow during and after rainfall, which increases storm water in drainage systems in built-up areas. Thereby reducing the level of percolation and increased overland and peak flows. The amount of runoff induced from urbanization has increased pollution and contamination of water bodies in the environment, which leads to serious environmental consequences (Parkinson, et al, 2010). The traditional model of storm water management is based on a misconception by people mainly to drain urban runoff as quick as possible from the environment through channels and pipes and this increases peak flows and costs of storm water management in urban system. Such solution has resulted in problem transfer from one place to another in the basin. The composition of urban water runoff is composed of high level of toxins such as metals which is as a result of not treating them before discharge (Parkinson, et al, 2010).
A more sustainable approach in managing storm water to prevent flooding and environmental degradation is Integrated Urban Water Management (IUWM) (UNEP, 2009). The IUWM system uses the following activities:
I. Enhance improved supply and efficiency in water consumption
II. Ensures that state of the act technology is put in to the system to make available quality water supply for drinking and other uses
III. Allows the diversification of water supply sources
IV. Bring about improved community system and education on water management
V. Encourage sustainability in management practices
VI. Sustain capacity building and development of institutions and personnel that are involved in IUWM system; and
VII. Makes for investment in the proper and efficient use of water
Many techniques have been developed by the IUWM system for storm water management over the years. These techniques have been applied in many urban areas, they include retention ponds, detention ponds, permeable surfaces, rainwater harvesting, green roof, constructed wetlands, infiltration trenches, grass filter strips, grass swales, pervious pavements, infiltration basin, surface and subsurface groundwater recharge, and other sources control measure (Perkinson et al., 2010).
2.1.1 Retention Ponds
This technique is one of the prominent storm water management in an environment. Retention ponds are designed primarily to enhance the quality of water from storm water flows and also employed as flood control devices in the environment. They are to remain in use in either dry or rainy seasons.
2.1.2 On-site Detention (OSD)
On-site Storm water Detention (OSD) method involves collection of the storm water or runoff such as rainfall on a site and store the storm water or runoff for a period, and then releasing the water gradually to the environment so that it doesn’t increases downstream flooding (Parkinson, et al, 2010; UPRCT, 2012).
2.1.3 Rainwater Harvesting
This technique essentially is to collect rainwater as a water resource in urban areas. This method is to increase and provide a combined benefit of conserving potable water and reducing storm water runoff in an environment. This technique is the collection of rainfall upon a catchment surface, such as roof of buildings and transport the rainwater into a storage tank for the neighbourhood use, landscaping, maintain water cycle balance, irrigation and pressure washing.
2.1.4 Green Roofs
Green roofs are also known as living roofs or rooftop gardens. This technique consists of thin layers of vegetation and growing medium installed on top of conventional flat or sloped roofs. There are benefits to green roofs methods in cities as they improve energy efficiency, as well as reduce urban heat island effects, and create opportunities for green passive recreation thereby enhancing the aesthetic values of the city environment. Green roofs also provide irrigation with treated grey water for water resources management; and they increase water quality, water cycle balance, and peak flow control in the environment especially urban areas (CVC & TRCA, 2010).
2.1.5 Constructed Wetlands
The method is an efficient engineering technique for storm water control and management. Apart from the constructed wetland other wetland could be engineered to manage storm water thereby improving the quality of water to preserve plant and animal species (Auckland City Council, 2011).
2.1.6 Infiltration Trenches
These techniques involve the excavating or digging shallow trenches and are filled with uniformly crushed stone which look like soaking pits to create underground reservoirs for storage of storm water runoff in the urban areas. The runoffs stored in the trenches after trapping of runoffs are slowly infiltrated through the bottom of the trenches into the subsoil and finally into the water table in the environment. The walls and the top area of the trenches are constructed with geo-textile materials to avoid sediment penetration to the water table to serve as preventative measure for groundwater contamination (CVC & TRCA, 2010).
2.1.7 Grass Filter Stripes
This is in another work referred to as filter stripes are techniques applied to densely vegetated area in the urban environment in a uniformly graded areas for the treatment of storm water from the surface. Grass filter stripes main function is to slowdown runoff velocities, trapping of sediments and other pollutants and providing a self-effacing infiltration to improve water quality. The various trees, shrubs, grasses and plants that will be employed also improve the aesthetics of the urban environment. This technique is used as pre-treating runoff method before storm water can send to a treatment facility where they are available (Barr Engineering Company, 2001).
2.1.8 Grassed Swales
Grassed swales are also called vegetated swales. They are techniques were open grassed channels is created in which storm water runoff from roofs, roads and public car parks are hold back slowly and sediments in the runoffs are infiltrated along the swales paths to prevent flooding and water contamination.
2.1.9 Pervious Pavements
Pervious pavement technique is a permeable pavement surface with a stone reservoir beneath it surface having drains which infiltrate storm water. This reservoir temporarily stores surface runoff before infiltrating it into the sub-soil drainage and this improves the water quality in the environment. This method is mostly used in roads with low traffic, parking lots, driveways, pedestrian and walkways. The underneath materials used for pervious pavement include grass, gravel and sand or topsoil and this depends on the type of soil in the environment for infiltration. Sometimes drainage is constructed under pervious pavement surface for partial infiltration while sometimes there will not drainage for natural infiltration to take place (Adapted from TECOECO, 2012).
2.1.10 Infiltration Basin
This is the construction of storage facilities in the high permeable soil zones to store water temporary from runoff in an urban environment. The infiltration basin practically does not have a structural outlet in its design such as the detention basin which easily discharges runoff from the storm water but runoffs outflow through the soil within the infiltration basin naturally to improve the water quality of the underground water system. The infiltration basin can also be integrated by extending it with a detention basin to provide additional runoff storage and achieve storm water quality and quantity management in the process (NJDEP, 2004).
Cost Considerations
Cost is a major consideration in the employment of any of the above techniques or methods. The costs of these different methods largely depend on the level of technology, topography and expert knowledge of the methods. Some of these methods for storm water management are easy to implement, others are very complex and expensive because of technology and expert knowledge and training for implementation and maintenance. On the other hand, a proper storm water management avoids damages on infrastructure and protects the population of urban areas and rural settlements.
Health Aspects
Most of the contemporary storm water techniques and methods have some ecological effects with the general aim to protect the health, welfare and safety of the public by preventing water pollution and contamination to reduce health risks and to protect buildings from flood hazards by carefully directing the discharging storm water from developments (CSIR, 2000). The problem for the public health associated with storm water management can be achieved through proper solid waste management. The exposure of the environment to waste during high floods leads to washing of contaminants to surface water bodies even groundwater contamination. Furthermore, high loads of sediments can clog infiltration which can lead to ponding in an environment and create breeding grounds for mosquitoes in humid climates where malaria and other tropical diseases are common (Parkinson et al., 2010).
Operation and Maintenance (O&M)
All storm water management systems need proper O&M services that are environmentally friendly and sustainable. Regular maintenance of storm water infrastructure extends the life of storm water systems and practices, improves built area drainage, and reduces pollution entering surface water and groundwater. Governmental facilities as well as private property owners are responsible for O&M practices in any urban environment and regulations and standards should be applied appropriately (Beat, 2012).
Applicability
Storm water management is necessary in every settlement whether rural or urban, to protect human health, prevent water pollution, reuse precipitation water on agriculture or household levels and prevent damages to infrastructure. Though, this is more crucial in urban areas as there are more concretized surface constructed and have change the hydraulic properties and prevent infiltration of storm water. In applying any storm water management method, the method has to be adaptive to the local conditions of the environment considering factors such as climate, topography, resources, level of technological advancement etc. therefore, expert knowledge is required (Beat, 2012).
2.2 Strategies for Storm Water Management
Generally, rivers are major contributor to storm water problem which results to flooding incident. When they generate flood, their impacts are devastating which destroy livelihoods, cause economic damage and even kill people. This is why humans look for ways to handle them to prevent flooding in the first instance or reduce the impacts. Though, rivers are nature creations that are difficult to predict and they are very powerful. Man’s ability to totally stop them from causing flooding is impossible but can control them to reduce impacts on human and the environment. However, to manage storm water not to cause flood, there are two basic storm water management strategies covering hard and soft engineering projects. Hard engineering projects are concerned with construction of artificial structures, through the combination of science, technology and a bit of force to prevent rivers and rainfall from causing flooding. Soft engineering projects are the opposite. These projects use natural resources and local human knowledge of the river and precipitation to reduce the risk of flooding (Alex, 2013).
The hard engineering projects are usually successful but have significant impact on the river system and this is their major challenge. The hard engineering approaches most times store large quantity of water when released, their impacts are worse when the river flows naturally. The cost of construction, operation and maintenance are very expensive and requires a lot technology, expertise and a lot economic resources are involved (Alex, 2013).
The soft engineering projects are centred on reducing and mitigating the impacts of storm water problems resulting to flooding incidents rather than preventing them. The major benefit of soft engineering is cost efficiency and effectiveness as they are cheaper to embark upon which developing countries can also undertake. The construction, operation and maintenance approaches low implication in education and technology requirements in implementation. Generally, they don’t disturb the natural processes and ecological systems in river basin like their hard engineering project counterparts but integrate with the natural system to achieve environmental sustainability (Alex, 2013).
2.2.1 Hard Engineering Techniques
2.2.1.1 Dams
Dams are super and hard engineering techniques with giant walls used to hold back water along a river course and are built across rivers. They curb flooding challenges in the environment especially settlement along rivers and floodplains. The magnificent engineering edifies hold water as reservoirs and drain water slowly in a controllable manner as not to cause water surge. This helps keep discharge downstream of the dam low even during prolonged heavy rainfall for months. Apart from mitigating flooding occurrence it also provides hydroelectric power to many settlements that enhances socio-economic growth and development. The reservoir of the dam can also be used for provision water supply and recreational activities (Alex, 2013).
In spite of these enormous benefits, dams have many environmental challenges impacts. Dams are expensive and highly technological demanding of all hard engineering techniques in the world as many resources are required for its construction. The settlements behind a dam have serious flooding often times that can destroy habitats and properties, force the inhabitants to leave their homes. Dams disrupt the natural processes that take place within the river ecological systems by not allowing sediments from being transported to downstream of the river and this can destroy landforms and habitats of the deltas. Also, the chemical composition is affected which can reduce the survival of aquatic lives (Alex, 2013).
2.2.1.2 Artificial Levees
Artificial levees are artificial versions of the river edges. They act as embankments just like their natural counterparts, and basically extend the channels height and increase their bank-full discharge. The primary benefit of an artificial levee is that it allows the floodplain to be developed upon which also have environmental consequences as it increases the risk of flooding from precipitation and river surge to the people that occupies the area and create ecological imbalances in the environment. However, if they fail, the consequences are overwhelming and even worse that if the levees did not exist at all (Alex, 2013).
2.2.1.3 Wing Dykes
Wing dykes are slats constructed and placed in river channels at ~90˚ to the banks of the river. The dykes are placed in pairs on either side of the channel of the river with a gap between them that allows boats to pass through them for navigation purpose. Placing dykes in the river, over the time sediment builds up and narrows the channel making water to flow faster. This helps reduce the risk of flooding by getting water away from an area at risk of flooding as quickly as possible, preventing a build-up of water. The disadvantage of wing dykes is that as it reduces the risk of flooding in one area, downstream of a river may experience risk of flooding making them only useful in low populated environments (Alex, 2013).
2.2.1.4 Channel Straightening
This method for flooding checking involves the blocking off meanders by constructing alternate and straighter routes across meanders, for the river to flow are faster and easy in movement. Like with wing dykes, this technique channel river water in a faster mode thereby preventing it from pooling at a point and causing flooding risk. A straightened channel is faster to navigate water and straightening channel. This technique has several problems; the downstream of a straightened section of a channel most times faces flood and erosion problems because of river dynamics (Alex, 2013).
2.2.1.5 Diversion Spillways
These are artificial channels created that a river can flow into when its discharge rises above normal level. These channels move water around an area to prevent the risk of flooding and direct the water back into the river of the downstream or into another river. Diversion spillways generally have floodgates on them that will be used to control the flow and volume of water in the river. Spillways pose a threat to areas near the confluence between the spillway and the river which can cause flooding as a result of overflow.
2.2.2 Soft Engineering Techniques
2.2.2.1 Flooding Zoning
This involves the preparation of restriction in floodplains on what landuse that be allowed in the area. Fundamentally, carrying major development in floodplains is limited but only developments that will promote, enhance and are environmentally friendly are allowed. Such developments are mostly recreational and tourism related activities are allowed which will not significant impact negatively on the environment and its natural habitats. These types of activities reduce the risk and impact of flooding. Basically, if developments are not allowed in this environment such as major residential development, industrial and manufacturing activities and commercial development the occurrence and damage of flooding will be greatly reduced. In addition, floodplain zoning ensures that land on the floodplain isn’t urbanised so infiltration can occur and surface runoff is reduced as these areas are the natural retention ponds. The major challenge with floodplain zoning and regulations are that development can be limited to these areas and if it has been developed over the years it will lead to forceful eviction of the people occupying the area and it limits development to certain areas (Alex, 2013).
2.2.2.2 Afforestation
This method involves the planting of trees in a drainage basin to increase interception and storage while reducing surface runoff. This activity reduces the velocity of runoff and also rivers inundation and decreases the risk of flooding of the environment. Afforestation helps reduces the amount of top-soil that are washed into the river and discourages erosion effects along river areas. The problem of afforestation is that large portion of land is needed for the purpose which encumbers farmers in floodplains in farm expansion. Though, this can be handled by creating riparian buffers , thin vegetated strips of land that run adjacent to a river’s channel (Alex, 2013).
2.2.2.3 Wetland Restoration
Wetland restoration is an environmentally friendly concept and it involves creating conditions that are favourable for the development on wetlands. Wetlands are marshy and swamps that can store large volume of water from rainfall in the environment and thereby reduce the velocity discharging water in a sustainable manner naturally. Wetlands do not reduce flooding where they are located but rather downstream of the river. The major benefits of wetland restoration are that wildlife and fauna are protected and preserved and also introduces new habitats to the environment thereby increasing the biodiversity of the environment. They are recreational and tourism potential for socio-economic and cultural development (Alex, 2013).
2.2.2.4 River Restoration
River restoration involves restoring a river that has undergone hard engineering activities back to its original state or course. This involves re-aligning of river channel, removing artificial levees, diversion spillways and wing dykes. River restoration is a good thing if it’s done properly as allowing the river to take its natural course prevents and reverts any environmental and ecological damage introduced by hard engineering projects. River restoration also has as well as zero (0) maintenance costs making it very cheap. Problem that arises during river restoration process in any areas is that people still used the river. Though, sometime a land may not be valuable and requires restoration. This decision comes down to the local environmental agency. If they make the wrong call, the restoration project can cause a lot of damage (Alex, 2013).
2.3 Problems of Urban Flooding
Urban flooding is a serious and growing phenomenon affecting both developed and developing countries. However, with the growing rate of rapid urbanisation, climate change leading to changes in urban hydrology; events such as urban flood is increasing rapidly (Amoako, 2012). Urban flooding events have caused massive distressing effects on many aspects of urban life especially on the residents, their economy and environment (eschooltoday, 2010).
2.3.1 Economic
Nevertheless, at the events of urban flooding residential developments, access roads, electricity, schools, hospitals and other infrastructures and facilities in the urban area are affected and or destroyed. This impact makes inhabitants of the urban area to be homeless and displaced for some time. In such events, government spent large economic resources by deploying emergency services personnel such as firemen, police, even the military and other emergency apparatuses to help evacuate affected persons. In the case huge financial resources is required by government to carry out this responsibility and people also will experience valuable economic resources destroyed or lost during the flooding events. This always takes time and huge financial resources to re-build these affected infrastructures and facilities destroyed for economic and social activities to come back to normalcy (eschooltoday, 2010).
2.3.2 Environment
The environment is the primary source of life to human and other living things. Therefore, when flooding occurs is the environment, the environment suffers one of the most devastating effects. This effect of the impact of flooding increases large amount of concentration of pollutants on the environment which stays for a long time and destroy the soil and contaminant natural water bodies within the flood area and this substance causes imbalance to the biological lives and ecological systems in the environment.
2.3.3 People, Animals and Plants
Humans, animals and plants the most affected creatures in the environment when urban flooding occurs as most of the world human population are concentrated in urban areas. This flooding causes huge human lives loss and injuries, and even causes several diseases and sicknesses as a result of pollution. As water supply and electricity distribution are disrupted people struggle and suffer which leads to infections such as military fever, pneumonic plague, dermatopathia and dysentery. Even animals and plants are affected as their natural habitat are polluted and destroyed and cause a lot of havoc in the environment and general survival challenges (eschooltoday, 2010).
2.4 Effects of Climatic and Hydrological Factors on Storm Water Management
The magnitude and frequency of large rainfall events present significant challenges for storm water management which most times the transporting system such as drainage are overwhelmed and filled beyond capacity and over flow and most coastal areas are exposed to risk of flooding (Liebl, 2011). For example, the U.S. Geological Survey (USGS) has created a synergy with the City of Charlotte and Mecklenburg County in North Carolina, and develop Flood Information and Notification System (FINS) used to check and address rapid flooding in the area by notifying future flooding occurrence in these urban areas where streams rise and fall rapidly (U.S. Geological Survey, 2003).
The FINS is based on a large network of stream flow-gagging and rainfall stations that will broadcast information recorded through radio telemetry. This system routinely notify the National Weather Service (NWS) and emergency agencies to respond rapidly in the region when rainfall and stream flow which indicate the eminent risk of flooding occurrence, for the agencies to issue warning signals to the people for evacuation and preparedness in the areas if necessary (Konrad, 2014; Carter, 1961).
Water bodies such as streams, rivers, lakes, etc are naturally fed by runoff from rainfall and snowmelt moving overland or subsurface flow. Flood incidence may occur when large volumes of runoff flow rapidly into water bodies and overwhelm the banks of these water bodies causing inundations and rivers surge. The rapid discharge of water that causes flooding is influenced by many factors including the intensity and duration of rainfall and snowmelt, the topography and geology of natural water basins, level of vegetation in the environment, and the hydrologic conditions prior storm and snowmelt events (Konrad, 2014).
Modest storage capacity for water from rainfall and snowmelt in urban basins, generate more rapid runoff and urban water bodies rise more rapidly during storms and have higher peak discharge rates than do rural streams. For example, stream flow in Mercer Creek, an urban stream in western Washington, increases more quickly, because of higher peak discharge and volume during the storm in 2000, and decreases more quickly than in Newaukum Creek, a nearby rural stream in the same region. These differences cannot be attributed to landuse patterns in the various creeks but reflect differences in geology, topography, basin size and shape, and storm patterns (Konrad and Booth, 2002).
Hydrology effects of urban development and most time significant in small stream basins where before urban development, much of rainfall on the basin would have become subsurface flow, recharging aquifers or discharging to the stream network. Urban development can totally change or alter the landscape in a small stream basin, unlike in larger river basins where areas with natural vegetation and soil are likely to be retained because of the extent of land and water basin (Konrad, 2014; Leopold, 1968).
Developing along stream channels in floodplains may distort the capacity of water channel to transport water which may increase the height of the runoff. Buildings and other developments that encroaches on floodplain, such as bridges, can increase upstream flooding by narrowing the width of the channel and increasing the channel’s resistance to flow. Since, the water is at a higher stage as it flows past the obstruction, it can cause backwater which may give rise to inundation of upstream because of sediments and debris carried by the flood (Konrad, 2014; Bailey, et al, 1989). Small stream channels also can be filled with sediment and cause clogging because of the size of the culvert in the stream. However, such channels can be engineered through the conveying of floodwater and debris quickly downstream, which may benefit the area and balanced against the possibility of flooding in downstream (Konrad, 2014).
Erosion is another consequence of urban streams as it effects urban development. The frequent development in urban water bodies increases flooding and causes bank erosion along the water channel path. Where river channels have been altered and vegetation has been removed from channel banks, stream flow velocities will increase and enhance the transportation of sediment along the river rapidly. In many urban areas, stream bank erosion continued to be threat to roads, bridges, and other structures which is difficult to control even by hardening stream banks (Konrad, 2014).
2.5 Effects of Landuse on Urban Flooding
The regular changes in landuses connected with urban development affect storm water and flooding in many ways. This is because vegetation and soil are normally cleared before construction of roads and drainage networks in the environment thereby increase runoff to water bodies from rainfall and snowmelt. In this instance, the peak discharge, volume, and frequency of floods increase in the water bodies around the urban environment. Changes to stream channels during urban development can limit their capacity to transport floodwaters to these streams. Roads and buildings constructed in floodplains are very much exposed to flood risks and hazards, and including inundation and erosion as development persist. Information about stream flow and how it is affected by landuse can help communities reduce their current and future impacts on people and the environment (Konrad, 2014; Anderson, 1968).
The most common consequences of urban development are increased peak discharge and frequency of floods of urban area. Naturally, the annual maximum discharge in a stream channel will increase as urban development occurs, sometimes this increase masked by substantial year-to-year variation in storms, as is obvious in the annual maximum discharge rainfall changes. The effects of the impact of development in urban basins are most manifest for moderate storms following dry periods. The effect of urban development in the last half of the 20th century on small floods is evident in Salt Creek, Illinois and this experience is with great exception of an unusually large flood in 1987, large floods have increased by about 100% while small floods have increased by about 200%. Therefore, even little increase in the peak discharge of a large flood can cause huge damages and consequences in the environment (Konrad, 2014; Bailey, et al, 1989).
Landuse and other human activities also influence the peak discharge of floods by modifying rainfall and snowmelt falls through global climate change. This increases the volume water to be stored and runoff the land surface will discharge into water bodies in urban environment. In undeveloped areas such as forests and grasslands; rainfall and snowmelt collect and are stored on vegetation, in the soil column, or in surface depressions (Zarriello, 1998). When storage capacity is filled, runoff flows slowly through soil as subsurface flow. In contrast, urban areas, where much of the land surface is covered by roads, buildings and other concrete developments this storage capacity is less to accommodate the volume of rainfall and snowmelt. Construction of roads, buildings and other urban development often remove vegetation, top-soil, and depressions from the land surface suffers flooding (Leopold, 1968; Bailey, et al, 1989).
There are several techniques and approaches to mitigate and minimize flood risks and hazards in basins under development. Areas considered as flood-prone areas are put into recreational use such as parks and playgrounds that can bear the occasional flooding incidents. In these areas buildings and bridges are elevated with floodwalls and levees to withstand inundation as a protective precaution. In these areas drainage system are constructed by increasing their capacity to accommodation and transport high volume of water to rivers. Also in these areas rooftops and parking lots are design to store water to reduce the impact of floods in the areas. Techniques that promote infiltration and storage of water in the soil column, such as infiltration trenches, permeable pavements, soil amendments, and reducing impermeable surfaces have also been integrated into developed and emerging residential and commercial neighbourhoods to reduce runoff from these areas (Konrad, 2014).
Urbanization process contributes to increase volume and occurrence of flooding incidents and thereby exposing neighbourhoods to increasing flood risks and hazards. Information from authorities on the current stream flow provides a scientific foundation for flood planning and management in urban areas. This activity creates flood hazard maps based on stream flow data collected over the years some time may not be accurate currently and need regular study of the river flow for accurate data for analysis for updates for flood maps in urban areas under going frequent changes as a result of urbanization. Stream flow-gagging stations provide information on stream flow that will enhance design and development of new urban infrastructure and facilities such as roads, bridges, culverts, channels, and detention structures. However, storm water managers in urban areas and applying the information with rainfall data to appraise modern solutions that will reduce runoff from urban areas that may cause flooding. Also, real-time stream flow-gagging stations can collect data about stream flow and rainfall data available through modern communication sources; propose multiple profits in urban watersheds. This information provides guide to the flood manager what techniques to apply in flood control, emergency plans, and preparedness and evacuation operations in the event of flooding (Konrad, 2014).
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