GIS for Effective Wetland Monitoring in the North of Mauritius

(1)

Master Thesis

submitted within the UNIGIS MSc. programme at the Centre for Geoinformatics (Z_GIS)

Salzburg University, Austria

under the provisions of UNIGIS joint study programme with Goa University, India

GIS for Effective Wetland Monitoring in the North of Mauritius

by

Farook Nathire

U0523108

A thesis submitted in partial fulfilment of the requirements of the degree of

Master of Science (Geographical Information Science & Systems) – MSc (GISc)

Advisors:

Dr. Shahnawaz & Dr. Mahender Kotha

Port Louis, Mauritius, 23 December 2008

(2)

Science Pledge

By my signature below, I certify that my thesis is entirely the result of my own work. I have cited all sources I have used in my thesis and I have always indicated their origin.

Port Louis, Mauritius, 23 December 2008 Signature

(3)

Acknowledgements

At the very outset I am very much grateful to the Almighty for His grace and great favour for granting me courage, protections and support throughout the duration of this course.

I would like to express my sincere and heartfelt gratitude to the UNIGIS Team, particularly Dr Shahnawaz who have guided me in the lifelong learning that has allowed me to continue studies in my relevant field, Cartography. I am grateful to, Messrs Goolamally, Gopaul, Shaik Joomun, Ramjee, all other colleagues of Cartographic Section and friends with whom I have discussed GIS lengthily so as to exchange ideas and share knowledge.

My thanks go to all the tutors of UNIGIS for the support and guidance throughout the modules and thesis preparation. Special thanks go to my Supervisors Dr Shahnawaz and Dr Mahender Kotha, for the guidance and critical comments that made the research a success.

I would also like to thank the University of Salzburg of Austria, and particularly congratulate the UNIGIS MSc blackboard team for the excellent work done to guide the course participants.

My heartfelt gratitude goes to my wife, children and parents for their support and encouragement during my studies.

(4)

Abstract

Wetlands have important functions for the safety and welfare of humankind. They provide habitat for many species, play a key role in nutrient uptake, serve as the basis for many communities’ economic livelihoods, provide recreational opportunities, and protect local areas from flooding.

In the northern part of Mauritius, most of the wetlands are found in low lying areas along the littoral. These wetlands have been decreasing substantially in size from human intervention.

Parts of them have disappeared and the remaining ones have rapidly degraded owing to considerable unplanned developments during the last three decades. Encroachments and backfilling have been carried out partly due to a lack of public awareness of the importance of such wetlands for maintaining a healthy lagoon and mostly for profitable use due to highly demand lands for construction. The harm caused on the ecosystem with the disappearance of part of the wetland is complex to appraise.

The lack of adequate information on the actual status of the remaining wetlands makes it difficult for the authorities to evaluate their reduction in size, plan their conservation and prioritise restoration. No archived survey records are available to track their original extent and boundaries. The absence of accurate geospatial data affects the decision of local authorities, environmental engineers and town planners.

Geographic Information System (GIS) is therefore applied to establish an inventory of remnant wetlands and determine spatial and temporal changes. The system also assists in providing support for strategic decision making in the monitoring process of wetlands conservation and restoration.

Part of Grand Baie, a coastal village in the North of Mauritius, is selected as a case study since this area has all the attributes of a typical scenario with good effects of wetland loss and encroachment.

(5)

List of figures

Page

Figure 1 – Location of Mauritius in the Indian Ocean and the Study Area (Photo: Microsoft Virtual

Earth) ... 9

Figure 2 – Extract of Grand Baie Map 1:2,500 published in 1995 showing the three wetlands ... 13

Figure 3 ‐ Aerial Photograph of Grand Baie 1967 ... 32

Figure 4 ‐ Aerial Photograph of Grand Baie 1991 ... 32

Figure 5 – Satellite Imagery 2004 of the study area (Microsoft Virtual Earth) ... 33

Figure 6 – Georeferencing of the study area Image using ArcGIS 9.2 ... 37

Figure 7 – On‐screen digitising performed on enlarged image ... 38

Figure 8 – Land Cover Map of the study area in 1967 ... 39

Figure 9 – Example of applying Dissolve Tool ... 40

Figure 10 ‐ Feature to Raster Conversion using ArcGIS Conversion Tool ... 41

Figure 11 – Boolean Image of wetlands at Grand Baie in 1967 ... 43

Figure 12 – Boolean Image of wetlands at Grand Baie in 1991 ... 43

Figure 13 – Wetland Change 1967‐1991 using Boolean Techniques ... 44

Figure 14 – Wetland Change in the area 1991‐2004 ... 45

Figure 15 ‐ Change in wetland from 1991‐2004, using Intersect Tool ... 47

Figure 16 – Wetland change 1967 to 2004 ... 47

Figure 17– 30m Buffer zone around existing wetland areas ... 49

Figure 18 – Occupation within 30 m buffer zone in 2004 ... 49

Figure 19 – Bounding coordinates of Grand Baie wetlands for monitoring ... 51

Figure 20 – Wetland change 1967‐1991, using Boolean Technique ... 56

Figure 21 – Results of wetland change 1991‐2004 ... 56

Figure 22 – Backfilling of wetlands with debris and rubbish ... 59

Figure 23 – Fragmentation of wetland with backfilling observed in 2004 ... 62

(8)

List of tables

Page

Table 1 – Mauritius Referencing System ... 32

Table 2 – Land Use/Land Cover classification of the area of study ... 37

Table 3 – Matrix Table showing wetland classification in image 1967 and 1991 ... 44

Table 4 – Cross Tabulation results using 1967 and 1991 dataset ... 46

Table 5 – Cross Tabulation results using 1991 and 2004 dataset ... 46

Table 6 – Extent of Buffer zone areas ... 48

Table 7 – Areas of Built up and Vegetation in Buffer Zone ... 50

Table 8 – Results of Cross Tabulation 1967‐1991 and 1991‐2004 ... 57

Table 9 – Results of Overlay Intersection Technique 1967‐1991 ... 58

Table 10 – Land cover change in Grand Baie (1967‐1991 and 1991‐2004) ... 59

Table 11 – Land Use and Land Cover distribution in 1967, 1991 and 2004 ... 60

Table 12 – Extent of change in land cover between 1967 and 2004 ... 60

(9)

CHAPTER ONE

1.1 Introduction

It is estimated that 50% of the freshwater wetlands that existed in the beginning of the 20^th century had been lost worldwide (Spiers 1999). The increased demand for agricultural land associated with population growth is the most significant cause of wetland loss (Bergkamp &

Orlando, 1999 cited UNEP 2003). Wetlands continue to be lost, degraded and many of them are in peril. Mauritius is of no exception, wetlands are being deteriorated with the changing land use around them; they are drained for agriculture and filled for development.

The Republic of Mauritius is a small island country situated at longitude 58° East and latitude -20° South in the Indian Ocean, approximately 2400 kilometres off the South East Coast of Africa near Madagascar (Figure 1). It is of volcanic origin and covers an area of 1,865 square kilometres. It has a population of 1.3m inhabitants. The surface topography of the North of the island features a low and flat coastal plain.

Figure 1 – Location of Mauritius in the Indian Ocean and the Study Area (Photo: Microsoft Virtual Earth)

(10)

1.2 Background and status of wetlands in the North of Mauritius

Wetlands in the North are mostly located in low lying areas along the littoral and they play an important role in the preservation of the environmental quality of the coastal regions including the beach, lagoon and coral reef. This part of the island is an undulating plain that contains a series of marshes and pans. These marshes are tracts of spongy land that support low growing woody plants, rushes and reeds; the pans are closed basins that collect rainwater. Within this undulating topography, there are historic wetlands in the lower lying grounds with a water depth of less than 2m at high water mark and these are influenced by water that arise from overland flow or precipitation. These wetlands are termed depressional wetlands. Such natural areas of marsh are permanently or temporarily filled with static water where emergent vegetations typically reed-bed are mostly dominant. In addition, they are important and essential for the health, welfare and safety of people who live near them.

The wetland buffers of 30 metres are functioning poorly in this part of the island because of their common use for dumping construction material wastes and other debris, as well as their increasing urbanisation. Very few people living near these wetlands are aware of their importance as the latter are considered as being wastelands or “inexpensive” lands that could be reclaimed or changed for profitable use. Increased property values in these areas have created financial incentives to gradually backfill unusable land. The backfilling has been practised by several unscrupulous land owners, adjoining the wetlands, who have exploited the buffer areas during dry seasons for the purpose of gaining land of great value.

These owners, under the constraining influence of land promoters, have been abusing the existing loophole in the law. They have wilfully violated the restriction imposed by the local authorities and have disregarded the small fine they have to pay in case they are caught red- handed in their unauthorised activities of backfilling.

The resulting loss of wetland area has not only decreased potential water storage capacity and flood control, but has also minimised other wetland functions such as water quality improvement and wildlife habitat. The alteration of wetlands in the northern part of the island has not occurred naturally; human interventions have contributed to their substantial decreased in size and are putting them under more pressure with commercial and recreational activities in the tourism sector near them. The continuous destructions of wetlands through backfilling are causing serious imbalances that result in flooding of low- lying lands during heavy rainfall and degradation of the coastal zone. These wetlands no longer act as flood regulators. In fact, they represent a serious threat to the inhabitants of the regions during rainstorms and cyclones.

(11)

These historical wetlands of the northern part of the island hitherto provide benefits to the natural environment in their natural states. The coastal environment there has been affected at a comparatively much faster rate than other coastal regions around Mauritius. The land cover has been significantly altered with considerable unplanned developments. Serious impacts to the environmentally sensitive areas are perceived with regard to loss of habitats and extinction of plant and animal species.

With increased knowledge and appreciation of wetland benefits over the last few decades, the assessment and management of wetland are becoming a very serious concern for the Government. In 30th September 2001 Mauritius signed the Ramsar Convention (NPCS, 2008). It is only then that wetlands have been receiving a formal recognition of their environmental values. A lot of effort is being made towards delineating their limit, assessing their health, prioritising a restoration plan for their eventual preservation. The existing Laws of Mauritius do not consider wetlands in virtue of their environmental qualities but protect them in relation to fishing activities by virtue of the “Fisheries and Marine Resources Act of 2007”. It is limited in scope and considers only wetlands that are related to marine environment. A draft Wetland Bill is being prepared and will be ready for enactment by the Parliament of the Republic of Mauritius shortly. Meanwhile, during this lack of protection, freshwater wetlands, particularly those having a general proximity to lowland coastal areas at the north of Mauritius, have been under heavy development pressure and have reduced in size and fragmented. Therefore geospatial data are needed for a comprehensive inventory of these wetlands and their ecological health so that a management plan can be implemented for controlling permitted development.

1.3 Study area (part of Grand Baie village)

The area of interest for this study is a part of the village of Grand Baie of an extent of 250 hectares located in the northern coast of Mauritius. The area has undergone significant development over time and the changes that have occurred in the close proximity of wetlands are enormous. The topography of Grand Baie is characterised by gently undulating land that forms depressions near the coastal areas with a water depth of less than 2m at high water mark. The historic marshy lands with static water all year long or during long periods of time as well as native vegetation like reed-beds are located in these depressions.

Furthermore, the overall area supports a variety of land uses which include residential, commercial, and recreational development, all of which have experienced rapid growth in the past 25 years.

(12)

The wetlands at Grand Baie were hitherto low spots surrounded on all sides by gentle upslope with native vegetation and no surface water inlet or outlet. Their being filled and drained over time have created a fragmented wetland mosaic containing a lesser volume of water. During rainy season, runoff from higher grounds increases flooding risk and occurrence of diseases and illnesses. These wetlands are considered as a management priority because of increased in frequency of flooding of residential properties constructed in backfilled wetlands. As development proceeds, the unrelenting pressure on the wetlands at Grand Baie and the consequences for sustainable development of this important tourist destination entails an involuntary change that is spreading to areas near or around these wetlands.

The present study area is a good representation of degraded wetlands where considerable unplanned developments are causing enormous harm to them. Most of these developments are for human infrastructure including recreational activities related to tourism. The coastal environment has also been affected at a much faster rate with over-development; not enough attention has been given to the environment.

This northern part of Mauritius is an ideal study area to develop an application that can be used to a much larger scale for assessing other wetland areas of Mauritius. It covers the following three main wetlands that have been affected by human activities occurring near or within them (Figure 2):

(i) Grande Mare Longue, (ii) Mare Michaux ,and (iii) Mare Soyfoo.

There are other smaller patches of wetlands for which no specific name has been assigned.

(13)

Figure 2 – Extract of Grand Baie Map 1:2,500 published in 1995 showing the three wetlands

1.4 Problem statement

The most attractive coasts in the north of Mauritius are found in Grand Baie area where tourism industry has flourished with profound effects on the local economy. The considerable development that has taken place in the last two decades has exacerbated the physical characteristic of that particular region. The booming of the tourism sector has made it difficult for the authorities to handle and coordinate the rapid expansion of amenities on both land and sea. This over-development in a confined area has a serious impact on the land use;

thereby increasing the pressure around wetlands in the region. It has also caused depletion and loss of wetlands at an alarming speed. The magnitude of encroachment, despoiling and pollution is not yet known and calls for an evaluation methodology to determine the amount of loss and manage the remaining wetlands.

(14)

Therefore wetland assessment, monitoring and conservation are a major matter of interest for the Mauritian authorities. The reductions in size of wetland throughout the past decade are the main issues for concern. There had been no commitment to preserve the remnant wetlands in their undisturbed and natural states; no management plan for protecting wetland has so far been developed. The priority tasks for the authorities are to identify, delineate, classify, and evaluate them so that wetland monitoring can be successful.

Wetlands cannot be protected and managed without the help from other stakeholders and citizens living around them. The success of wetland monitoring and conservation will partly depend on the awareness of the public. The population residing near wetlands has to be aware of the danger that represents clearing of these natural environments to the diversity of wetland ecosystems. The sensitisation together with enforcement of the new wetland law will contribute in preventing further human destruction since in Mauritius, most of the wetlands are privately owned. In the absence of an appropriate legislation, defaulters have been using these wetlands as dumping sites. The latter has to be sensitised on the importance of wetland and the vulnerability of this world’s most valuable environments on which a variety of plants, animals and human communities depend.

Furthermore, the monitoring exercises of wetlands have to be complemented with up-to-date information. Spatial data in the form of Geographic Information System (GIS) maps or cadastral survey records on wetlands’ original boundaries are needed. Application of GIS tool is also required to detect changes and evaluate the extent of damages already caused to them which are really complex to ascertain. In fact, effective monitoring requires such analytical tool to support decision making in the planning of wetlands’ protection and their possible restoration.

1.5 Aims and objectives

Wetlands are currently receiving considerable attention in environmental science and policy.

With technological advances, it is now possible for the Mauritian authorities to measure how much wetland areas at Grand Baie have disappeared and to evaluate those remaining. The application of GIS is an important requisite in the processing of information for the area and in the preparation of a management plan for wetland monitoring.

The aims of the study are to develop a methodology for wetland monitoring using spatial analysis tools of GIS. The amount of change over time in the remaining wetland’s

(15)

characteristics is to be precisely determined. The monitoring exercise aims also at providing measures to conserve and make wise use of the wetland resources and subsequently putting an end to the progressive encroachment on and loss of wetlands. The approach in this study comprises (i) wetland identification, location and boundary delineation of wetlands, and (ii) development of a digital database required by GIS. The overall goal is to demonstrate the important use of GIS for the monitoring of wetland acreage change overtime which subsequently will require the implementation of the following tasks:

a) An inventory of remaining wetlands to assist the preparation of a management plan for their protection and conservation.

b) Collection of accurate spatial information from suitable source to measure the success of wetland protection.

c) Use of GIS in the assessment methods and to evaluate the nature of changes.

(16)

CHAPTER TWO

Literature review

2.1 Introduction

This chapter reviews some literature researches on inventorying, assessing, monitoring and managing wetlands using Geographic Information System (GIS) applications.

Mauritius, being a small island country, does not have that very large extent of wetland.

Therefore, the nature of change that results from loss and degradation of wetland due to development trend in Mauritius is not necessarily of the same magnitude to the countries or regions named in this review of literature. However some examples and experiences of other countries, gleaned from some literature review available on the Web, will be discussed hereunder and compared to our local conditions. An approach will then be developed to fit in the Mauritian context for assessing the effective use of GIS to monitor our wetlands.

2.2 Definitions of wetland

In Mauritius wetlands are commonly called marshy lands because they are low watery lands.

These wetlands represent areas where waterlogged soils occur and emergent vegetation, typically reed beds, is considerably present. The concept of wetlands also includes areas where water is the primary factor that controls the environment and the associated plant and animal life.

The world wide definition of wetland adopted by the Ramsar Convention is:

"areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres".

However, the United States Army Corps of Engineers and the United States Environmental Protection Agency jointly define wetlands as:

"those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetations typically adapted for life in saturated soils."

(17)

Since the coastal wetlands in the North of Mauritius consist of several scattered areas of marsh which are natural with water that is static either permanently or temporarily. The definition of Ramsar Convention (1971) is too broad for our coastal wetlands; so, the joint definition of United States Army Corps of Engineers and the United States Environmental Protection Agency is more appropriate to those wetlands of Mauritius.

2.3 Physical characteristics of wetlands

There are three main characteristics of wetlands to be considered when making wetland determinations. Many wetlands are easily identified by the general situation comprising indicators of the three wetland characteristics stated below.

 Soils indicators

Wetlands are found under a wide range of hydrological conditions, but at least some of the time water saturates the soil. The result is a hydric soil characterized by an absence of free oxygen at some time or permanently.

 Vegetation indicators

Plants (called hydrophytes or just wetland plants) specifically adapted to the reducing conditions presented by such soils can survive in wetlands such as cattails, bulrushes, reed weeds etc;

 Hydrology indicators

Generally, the hydrology of a wetland is such that the area is permanently or periodically inundated or saturated at the soil surface for a period of time during wet season. The amount of water generally fluctuates depending on rainfall patterns. Often the same wetland can appear to be an open body of water some times and a dry field at other times due to significant fluctuations in water levels.

Usually, most coastal wetlands in Mauritius are identified by the vegetation and hydrology indicators. They are termed depressional wetlands because they are lower in elevation than the surrounding topographic landscape in undulated flat surfaces. Because of their shape, they trap more water than some other classes of wetlands. Consequently, the length of time that water is present in depressional wetlands is greater than in other classes because water leaves the wetland only through ground water recharge or evaporation. The surface water hydrology in the island’s northern region is disjointed. The depressional wetlands receive the majority of their water from rainfall and adjacent surface water runoff. The native vegetative species and shrub cover are mainly dominated by “Typha Domingensis” known in Mauritius as “Voune”.

(18)

2.4 Ramsar Convention on wetlands

The Ramsar Convention Manual, 4th edition (2006)

The Ramsar Convention on Wetlands initiated in February 1971 draws international attention to the rate at which wetlands is disappearing, in part due to lack of awareness of their important functions. Wetland loss and degradation has primarily been driven by land conversion and infrastructure development, water abstraction, pollution and over- exploitation. Losses are more pronounced where populations are increasing most and where demands for increased economic development are greatest.The treaty initially focused on the conservation and wise use of wetlands basically as habitat for waterbirds. It has afterwards broadened its range of activities to cover all aspects of wetland conservation and wise use, recognizing wetlands as ecosystems that are extremely important for biodiversity conservation and for the health of human communities. Contracting Parties have expressed their willingness and commitment to redress the situation of wetland loss and degradation.

Large sum of money are being spent to restore lost or degraded wetlands because of the multiple roles of wetland ecosystems and their utility to humanity are increasingly understood.

In determining wetlands under its aegis that fit the abovementioned Ramsar Convention’s definition, the following five wetland types are recognized according to their characteristics:

 marine (coastal wetlands including coastal lagoons, rocky shores, and coral reefs);

 estuarine (including deltas, tidal marshes, and mangrove swamps);

 lacustrine (wetlands associated with lakes);

 riverine (wetlands along rivers and streams); and

 palustrine (meaning "marshy" - marshes, swamps and bogs).

The general objectives of the Convention provide to undertake effective implementation covering, inter alia, the following subject areas:

 Inventory and assessment

 Restoration and rehabilitation

 Management planning and monitoring of Ramsar sites

(19)

According to the Ramsar Secretariat, it is essential to have adequate knowledge of wetland functioning so as to manage them effectively. The proper management of wetland requires complete inventory, assessment, strict monitoring, research and training activities.

2.4.1 Framework for wetland inventory, assessment and monitoring

The Ramsar Resolution on Integrated Framework for Wetland Inventory, Assessment and Monitoring (IF-WIAM) lays stress on the importance of assessing and reporting the status of wetlands as well as monitoring for their conservation. The Scientific and Technical Review Panel (STRP) of Ramsar provides guidance to Contracting Parties on various aspects of wetland inventory, assessment and monitoring in the form of an integrated framework.

The objectives of the resolution embodied in the Ramsar Convention entail:

a) establishing the location and ecological characteristics of wetlands (baseline inventory);

b) assessing the status, trends and threats to wetlands (assessment);

c) monitoring the status and trends, including the identification of reductions in existing threats and the appearance of new threats (monitoring); and

d) taking actions (both in situ and ex situ) to redress any such changes causing or likely to cause damaging change in ecological character (management).

Although there is a relationship between wetland inventory, assessment, monitoring and management, the approach and the scope of activity for inventory, assessment and monitoring as separate components of the management process differ. The working definitions for wetland inventory, assessment and monitoring are incorporated into Ramsar’s Framework for Wetland Inventory (Resolution VIII.6) as follows:

Wetland Inventory: the collection of core information including wetlands’ ecological character for wetland management, as well as the provision of information base for specific assessment and monitoring activities.

Wetland Assessment: the identification of the status of, and threats to, wetlands as a basis for the collection of more specific information, such as pressures and associated risks of adverse change in ecological character, through monitoring activities which include survey and surveillance.

(20)

Wetland Monitoring: the collection of specific information for management purposes in response to hypotheses derived from assessment activities, and the use of these monitoring results for implementing management. The collection of time-series information that is not hypothesis-driven from wetland assessment is here termed surveillance rather than monitoring (Resolution VI.1).

Mauritius became a member of the Ramsar Convention in 2001 (NPCS 2008). As a Contracting Party, it has to complete its national scientific inventory of wetland and to give the inventory highest priority. The status of remaining wetlands and the threats to wetlands have to be assessed. Data management through the use of remote sensing and GIS is being envisaged. Monitoring will require a process to quickly determine change over a period of time by using GIS, simple field surveys, GPS and remote sensing. The aim of monitoring is to collect time series information about wetland status so as to determine prevailing threats to these wetlands.

2.5 Geographic Information System (GIS)

A GIS is a computer system capable of capturing, storing, manipulating, analyzing, retrieving and displaying geographically referenced information; that is, data identified according to location. It also includes systems designed to capture spatial information and to process it.

Large amount of geographic data can be analysed as a whole to provide useful information for planning decisions. A GIS brings together spatially referenced statistics and remotely sensed imagery into one integrated system. It presents information to users in a language and format that is not only accurate, but also comprehensible. Practitioners also define a GIS as including the procedures, operating personnel, and spatial data that go into the system.

GIS can integrate and relate any data with a spatial component, regardless of the source of the data. It is also widely used for explaining events, predicting outcomes and planning strategies (ESRI). GIS has been developed over the years to become a powerful vehicle for information management and decision support. Environment decision makers derive much benefit with the functions of GIS to visualise, organise, combine and analyse data to produce new data in order to provide answers. The most powerful characteristics of a GIS are the ability to produce graphics instantly on the screen to show results of analyses to managers or decision makers. Images generated are helpful in conveying technical concepts of a GIS to non-scientists.GIS also allows interactive queries of information contained within the map, table or graph.

(21)

2.6 GIS in effective wetland management

There are a number of publications and studies showing the use of GIS in wetlands management. Wetland managers and conservationists need not rely on GIS experts to make simple queries in the performance of their duties. Palminteri et al (1999) discuss the

“Applications of a user-friendly GIS to Wetlands” in the “Ramsar COP7 DOC. 19.4”. It has demonstrated how GIS improves the ability of managers with little computer skills to understand and interpret data to obtain solutions. GIS has been used to present information and predict future situations on the basis of current activities. They have also found that geographic processing of spatial data is beneficial in ecological monitoring and in the fields of research to generate new information.

Distribution analysis has been accomplished in a user-friendly GIS for habitat types or seasonal movements of human being or animals using satellite images combined with field data collected by GPS. The authors have pointed out that satellite images at given time pertaining to various types of vegetation and current land use of an area are determinant in detecting changes in vegetation, water quality and water quantity when comparing the images with either those of earlier or later.

A variety of natural and human factors such as slope, soil type, water table, endangered species distribution, land price, transportation corridors and population movements have to be considered for the efficient planning of wetland conservation. This will help wetland managers to react appropriately to changes in either of these factors.

The authors conclude that wetland managers/conservationists have to learn easy-to-use GIS to be effective and not relying on GIS specialists to input, update, view, analyse and display information. A user-friendly and low-cost system is found very useful for wetland conservationists to carry out operations reviewed above thereby ensuring ecological monitoring, management and preservation of wetlands.

2.7 Change detection using GIS tools

The earth surface is being continuously altered due to the constant demand for development to suit human activities. The natural state of the landscape is being transformed into intricate pattern in the land use/land cover over time. Hence information about land is fundamental for monitoring the dynamics of land use and environmental changes. Over the past years, data from remote sensing have been of immense value in mapping the earth features, managing

(22)

natural resources and studying the environmental change. Remote sensing and GIS have provided new tools for analysing changes that have taken place in a specific region so as to predict possible future changes within the same region.

A variety of change detection techniques have been developed over the last two decades.

Hyyppa (2002) and Coppin & Bauer (1996) summarize the following change detection methods:

1. Mono-temporal change delineation.

2. Delta or post classification comparisons.

3. Multidimensional temporal feature space analysis.

4. Composite analysis.

5. Image differencing.

6. Multitemporal linear data transformation.

7. Change vector analysis.

8. Image regression.

9. Multitemporal biomass index.

10. Background subtraction.

11. Image ratioing.

Image-to-image or pairwise comparison approach supports various techniques based on the functionality of Image Processing and GIS system such as:

 Image differencing - subtracting pixel by pixel from two co-registered temporal images.

 Image ratioing – computing the ratio of the values of corresponding pixels between two temporal images.

 Image regression – assuming that the pixel values of the second image to be a linear function of the corresponding pixel values of the first image.

 Principal Component Analysis (PCA) – applying to either each of the multispectral multitemporal images so that the principal component of each data is compared with one of the above methods or is applied to a combined image consisting of combined bands of images to be compared.

Wetland change detection involves the application of multi-temporal datasets to quantitatively analyse the temporal changes on historic wetlands. The benefits of repetitive data acquisition, remotely sensed data, its synoptic view, and digital format suitable for computer processing, are the major data sources for wetland change detection applications during the past decades ( Fogel 2006 , Kuhn 2000, Lu et al. 2004 ,

(23)

Munyati 2000 cited Baker et al. 2007 ). Change detection research provides the following main information:

(1) area change and change rate;

(2) spatial distribution of changed types;

(3) change of land-cover types; and

(4) accuracy assessment of change detection results.

The complexities of factors to detect change have resulted in controversial conclusions about which change detection techniques are most effective. It has been difficult to select a suitable algorithm for specific change detection. Hence, a review of methods used in previous researches helps to chose techniques that can be best used to address specific problems. Identifying a proper methodology also depends on the selection of data for assessing change. Different source data associated with different data accuracies and formats often affect the change results.

The powerful GIS functions provide convenient tools for the multi-source data processing and are effective in handling the change detection analysis. GIS approaches have shown many advantages over traditional change detection methods in multi-source data analysis.

Feature-based approach uses various tools for spatial analysis such as:

 Layer union

 Layer intersection

 Buffer generation, and

 Topological overlay

The tools are selected on the basis of the data source and the required outputs. The accuracy, reliability and completeness of the results may vary from one application to another.

However, Macleod and Congation (1998) list four aspects of change detection which are important when monitoring natural resources:

i. Detecting the changes that have occurred ii. Identifying the nature of the change iii. Measuring the area extent of the change iv. Assessing the spatial pattern of the change

In the document “A Visual Learning Systems, Inc. White Paper April 2004”, the use of change mask techniques such as Image Differencing, Image Ratioing and Image

(24)

Regression, do not provide sufficient information to the GIS and image analysis community as regards to change detection based on specific criteria or categories. Moreover, categorical change extraction techniques such as Change Vector Analysis, Post- Classification Comparison, and Direct Multi-date Classification, are expensive. These methods depend on the accuracy of scene classification, require expert computer programming, and most importantly, they do not produce an adequate level of accuracy to be useful for most domains.

The Feature Analyst Professional, mentioned in the above White Paper, is the first viable automated change detection system that allow users to quickly update their GIS data layers so as to reflect the changes over time. With the decreased in the cost of high-resolution imagery, the need to update geospatial data has become more pressing to support accurate and timely decisions.

The methods highlighted above show proper methodologies for determining change in land cover using satellite imagery. However the processing of such imagery through the advance of technology has become much cheaper and requires less investment as it was before.

Temporal data are also more readily available through a large palette of satellite imagery providers, allowing changes in land cover to be detected more promptly. Low cost GIS software is also available and there is no need for expertise in GIS to update geospatial data.

2.8 GIS for Wetlands Health Assessment

Wetland conservation is a major issue for those who are concerned with the protection of the natural environment. The reason for this concern is due to the steady loss of wetland areas throughout the past. For a proper assessment, wetlands are first identified, classified and evaluated for remediation strategies (Dugger 1997).

In the document “A Strategy for the 21^st Century”, the National Wetland Inventory (NWI) of the U.S. Fish and Wildlife Service has made extensive use of aerial photographs dating from 1971 to 1992 supplemented by soil surveys and field checks to create a database for locating and classifying wetlands for the entire United States. The land cover change is clearly spotted in only a few years. The coverage describes the vegetation, water bodies limit and the natural land surface. The classification coverage is the most important data in the analysis of NWI using GIS programs (ArcInfo); skilled work has been performed before

(25)

an accurate assessment of wetland health is conducted using land cover and water quality.

The NWI dataset consists of elevation, soil type and rainfall for assessing the relative health of wetland environment. These data sources have been crucial in depicting changes in the wetland characteristics over time. They are available to the public. In 1998, the Wetlands Interactive Mapper was introduced to allow personal computer users to produce wetlands maps for any area that had digital wetlands data available.

To refocus the inventory of wetlands, the uses of latest scientific and technical tools for analysing information are required to enhance the GIS aspect which has so far been successful in the inventory work of NWI. It has been concluded that GIS provides the NWI with not only a means of assessing the health of natural wetlands, but also provides the results of current attempts to create new wetlands and their impacts on the ecosystem as a whole.

2.9 GIS in assessing areas of rapid wetland change

With time, approaches in rapid assessment of wetland have improved. The traditional method of evaluating a single site for a single function or problem has been superseded by larger area models. The latter combine variables and parameters to assign functional indices to various wetlands in a watershed. The approach incorporates wetland measurements and landscape characteristics for evaluating the capacity of wetlands to perform a number of functions. The model requires input of the following datasets: soils, land use, land cover, wetland boundaries, hydrography, roads and watershed boundaries.

The “Wetland Status and Trends Unit”, component of the NWI, monitors changes in wetland acreage for the United States. Specific geographic areas where wetland losses are at unusually higher rate than the average are identified. The areas mostly affected are those where rapid land use changes are on-going due to population increase, agricultural practices or changes in land values. GIS has been used in the process of locating these “hot spots”

and to also identify discrete areas where significant changes have occurred.

The “Wetland Status and Trends Unit” uses remote sensing extensively to monitor wetland acreage changes. Colour infrared aerial photographs of different dates are compared and site verification of changes previously carried out is recorded. This process has been necessary because of the time lag between the date of the photos and the actual analysis.

(26)

Past documented studies of “Wetland Status and Trends” (Dahl & Johnson 1991) revealed that the types of land use activities that most influence wetland conversions include:

Conversion to Agriculture – agricultural land use is required for production of food crop and fibre pasture, confined feeding operations, other agricultural land including livestock feed lots, etc.. Historically agriculture has accounted for between 50 and 80 percent of wetland losses in US.

Conversions to Urban Development – Urbanisation consists of areas of intensive use with much of the land covered by structures (high building density) including transportation and communication facilities.

Conversions to Rural Development - Rural developments occur in scattered rural and suburban settings outside distinct urban cities and towns. They are characterized by non-intensive land use and sparse building density.

Conversion to Forested Plantations - Plantations include silvicultural areas such as planted pines, Christmas tree farms, clear cuts and other managed forest stands.

Conversion to Other Upland Land Use - Land use is composed of uplands not fitting into the previous categories and including native prairie, unmanaged or non- patterned upland forests, scrub and barren land. Lands in transition from one land use type to another also fit into this category.

Wetland losses are likely to occur wherever the above land uses conflict with wetlands.

Losses are greatest where wetland abundance is greatest because possible conflict with land development activities is more prevalent. Consequently, future losses will probably be greatest in the areas of the country where an abundance of wetland acreage and a high potential for land use conversions overlap.

GIS data layers are adequately developed to represent the above land use conversion factors. These data layers are examined to determine where intersections with wetland complexes exist. In theory, these intersections represent potential "hot spots". Temporal data from remote sensing coverage with fine resolution of land use changes are preferred to create the GIS data layers useful for detecting wetland losses.

(27)

“Wetland Status and Trends” has created GIS layers from data provided in tabular format like recent population changes. All analysis, interpretation and display of data layers have been conducted in ArcGIS.

2.10 Remote sensing in wetland change detection

In the African Journal of Science and Technology, Volume 8, No 1 (AJST 2007), the use of remote sensing methodology for detecting seasonal change and inundation in the wetlands north of Lake George, western Uganda has been adopted. Landsat TM and ETM+ satellite imageries from 1987, 1995, 1999 and 2001 have been used to classify water bodies, exposed areas and vegetated zones. The three classified features have been generated in a GIS using: NDVI, NDWI and Unsupervised Classification supported with ground truthing so as to assess the changes that may have taken place over the above specific time period.

Change detection is the process of identifying differences in the state of an object or phenomenon by observing it at different times (Hyyppa 2002). Remote Sensing is cost effective for repeated observation of wetland change for monitoring as it provides timely and accurate change detection. Wetland change detection and inundation mapping using Landsat (MSS, TM, ETM+) has been applied extensively worldwide (Yang et al. 1999).

Incorporation of multi-source data (e.g. aerial photographs, TM, SPOT and previous thematic maps) is an important tool for land-use and land-cover change detection (Mouat and Lancaster 1996 cited Essa et al. 2006, Chen 2002, Weng 2002). The tool is much efficient when the change detection spans over long period intervals in different data sources, formats and accuracies or multi-scale land-cover change analysis (Petit and Lambin 2001). Weng (2002) uses the integration of remote sensing, GIS and stochastic modelling to detect land-use change in the Zhujiang Delta of China. It has been indicated that such integration has been an effective approach for analysing the direction, rate and spatial pattern of land-use change. Yang and Lo (2002) use an unsupervised classification approach using image clustering and cluster labelling. This is a GIS-based image spatial reclassification procedure to provide a solution for classification errors caused by spectral confusion and post-classification comparison with GIS overlay to map the spatial dynamics of land-use/land-cover change of the ATLANTA, Georgia metropolitan area of US.

(28)

2.11 GIS in prediction of land use change

The study on coastal research project of South Carolina has developed and applied GIS methodologies for analysis, modelling and prediction of coastal land use change. A spatial multivariate logistic regression model has been developed and 20 variables have been selected to predict the possibilities of land-use change for Murrells Inlet. The logistic regression model appears to be appropriate for the prediction of spatial land use change with overall success rates over 90%. The results has demonstrated the advantages of GIS over conventional methods in integrating various data sources, performing spatial analysis, modelling spatial process and mapping the results in land use change studies (Allen et al 1999).

Satellite imageries have been used for land use classification and change detection in environments like rural, urban and urban outskirts (Jensen and Toll, 1982 cite Wu et al, 2002; Fung, 1990 cite Chowdary et al, 2001). However, satellite images are found unsuitable for monitoring land use change particularly for planning tourism resources because the level of accuracy required was insufficient. Thus cadastral data or parcel data from building permits provide more information about land use change in finest spatial resolution and highest accuracy for small land parcel boundaries. The factors that influence land use change are so complex that predicting the change has been difficult.

2.12 GIS in planning wetland restoration

Bannon (2005) considers that threats of wetland ecosystems around the world come from various sources. Factors that mostly affect Wetland habitats are climate change, sea level rise, introduced species and human induced activities. These activities involve draining and backfilling of wetlands to create land for coastal development, dams and dykes to control tides and storm surge for minimizing the risk of flooding and finally ditch to reduce pools for breeding mosquitoes.

Thus, wetland restoration projects have been implemented in many parts of United States to combat loss of marsh acreage. The restoration process has been carried out in three phases: initial planning, physical work to be done on site and post restoration assessment and monitoring (Wilcox and Whillans 1999).

(29)

GIS has been successful in guiding the restoration of Metzger Marsh in western Lake Erie.

Kowalski and Wilcox (1999 cited Bannon 2005) have used digitized aerial photographs to study historical changes in land use, vegetation cover, and the Lake Erie shoreline. It has been found that the increase in water level over periods of time has caused marsh vegetation to drown and the rate of erosion of the barrier beach shielding the marsh from storm waves has increased.

GIS has also been used to assess the level of water quality, wildlife habitat and hydrologic functions of coastal wetlands. The North Carolina Coastal Region Evaluation of Wetland Significance (NC-CREWS), which is a watershed-based wetland functional assessment model, has used GIS to provide users with information for use in planning and management of wetlands. GIS applications have mainly been adopted as a planning and decision support tool rather than a decision making tool. They have assisted to define suitable classes, types, or categories of development or conservation practices of those ecosystems and calculate potential risk of wetland loss at the function level. The validity and accuracy of the NC- CREWS GIS databases used have been verified to the greatest extent possible.

One of the most common applications of GIS in wetland restoration is the preliminary cost- benefit analysis (Rozas et al 2005; Roise et al 2004). The cost-benefit analysis is considered important because wetland restoration is a long process that is not always successful. Out of 87 published studies of NC-CREWS for wetland restoration, only 20 percent were successful, 20 percent were not, and the rest fell somewhere in between (Keddy 1999;

Lockwood and Pimm 1999 cited Bannon 2005). Roise et al (2004) mention “unrealistically low cost estimates” and “overly optimistic expectations for marginal sites” as two contributing factors to low restoration success rates. Project costs are potentially reduced if much of the preliminary planning has been carried out using GIS rather than estimation by field crews.

According to Ashby (2002), scientists give little consideration to the ecological context in which restoration sites are located. The potential impact of the entire watershed has to be globally examined when planning the restoration of a single marsh. The connections between plants, animals, soils, hydrology, and human land use over an entire watershed are very complex and difficult to tackle with statistics. Therefore, maps of these features and the data imbedded in those maps in a GIS framework significantly reduce the complexity of the task. In her conclusion, Bannon (2005) remarks that:

 although GIS databases and tools such as DEMs, DOQQs, orthophotos and satellite imagery are available for use in wetland restoration, GIS has not yet been exploited to its fullest potential.

(30)

 GIS can increase efficiency and reduce costs during restoration planning.

 GIS can provide clear and informative presentations of complex data.

However, recommendation 4.1 of the Ramsar Convention rightly notes that the cost benefit analysis has a weakness. In its guideline for wetland restoration, the maintenance and conservation of existing wetlands is preferred as it is more economical than their subsequent restoration. Moreover, the currently available techniques for restoration cannot bring back conditions of the pristine natural ecosystems.

2.13 Analysis in planning methodology

GIS analysis has been used to identify historically filled or severely degraded coastal wetlands sites in the planning methodology of the Great Marsh Coastal Wetlands Restoration Plan (Massachusetts). The plan has been prepared and produced with the support from the Massachusetts Office of Coastal Zone Management's Wetlands Restoration Program for the Great Marsh region.

Aerial photographs, maps and data sources of the study area have been analysed through GIS technology to identify sites that have been backfilled or significantly degraded. GIS layers for the study area have been created from, digital orthophotos and topographic maps (1980, 2001 and 2005). Historical maps dated mid 1800s to early 1900s and historic aerial photos from the 1950s have been digitized and georeferenced.

These layers have been assembled into a single project file and analysed as overlapping layers using ArcGIS 9.0 software. Potential restriction sites have been observed where manmade infrastructure and landscape changes have blocked tidal flow to wetlands. The analysis has revealed over 250 suspected sites in Great Marsh region.

108 suspected sites have been identified to contain some level of restoration potential and they have been included in the Plan. These potential restoration sites have been further evaluated using GIS to determine appropriate options and other factors that could affect the restoration feasibility.

(31)

CHAPTER THREE

Methodology

3.1 Introduction

This chapter covers the means of data collection for the inventory of wetlands in the study area. The datasets include identification and accurate location of the wetlands using aerial photographs, satellite imagery and ground surveys. The building of a Geodatabase showing the different feature datasets and classes, methodology for wetland monitoring and GIS data analysis are also covered.

3.2 Spatial data acquisition

The collection of core information for wetland management, as well as the provision of information base for specific assessment and monitoring activities, is mandatory to establish the inventory. According to Longley et al., (2001), up to 85% of the cost to run a GIS is spent to acquire, input, update and manipulate data. So spatial data are the “life blood” of any GIS;

the acquisition of such data and information is now obtained in much shorter time periods compared to the past through remote sensing techniques. For this study area, data have been collected from various sources such as aerial photographs, digital maps, satellite imagery and ground surveys.

3.2.1 Aerial photographs

Building the profile of wetlands at Grand Baie requires a compilation of the best available spatial information on the wetland locations and boundaries. Aerial photograph is the only available source of data and information for ascertaining the existence of past wetlands and the land cover around their areas. Thus the mapping of land use/land cover near or around these wetlands is carried out using past aerial photographs taken in October 1967, October 1975, September 1991 and November 1998 archived at the air-photo library of the Ministry of Housing and Lands of Mauritius. The oldest aerial photograph available for Grand Baie dates 1967 (Figure 3) and it is used as the reference year for comparative analysis with photograph taken in 1991 (Figure 4). The classification of historical data is based on past topography and relative thematic maps.

(32)

Figure 3 ‐ Aerial Photograph of Grand Baie 1967

Figure 4 ‐ Aerial Photograph of Grand Baie 1991

3.2.2 Digital maps

Geographic data from existing large scale topographic maps of Grand Baie produced in 1978 and 1996 through photogrammetric procedures, using aerial photographs of 1975 and 1991 respectively, are used in the inventory process. These vector data have a planimetric accuracy of 50 cm and 15cm in height. Contours of the base maps are at 2 metre vertical interval. Map data derived from these large scale maps are used in the form of a layer in a digital map database during photo interpretation to locate and delineate wetlands boundaries. The reference system used is Lambert Conical Orthomorphic projection and Clarke 1880 Ellipsoid with false coordinates of 1,000,000m East and 1,000,000m North (Table 1).

Projection Type: Lambert Conical Orthomorphic

Spheroid Name: Clarke 1880

Datum Name: Le Pouce

Longitude of Central Meridian: 57° 31' 18.58" E Latitude of Origin of Projection: 20° 11' 42.25" S False Easting at Central Meridian: 1,000,000 meters

False Northing at Origin: 1,000,000 meters

Unit of Measurement Meter

Table 1 – Mauritius Referencing System

The maps are converted to a GIS format in shapefile for use or combine with other data layers during analysis with ArcGIS 9.2.

(33)

3.2.3 Satellite imagery

Image processing techniques represent a unique tool for monitoring wetlands. The repetitive coverage of the satellite provides an excellent opportunity to evaluate the land cover changes through a comparison of images acquired for the same area at different times. Although satellite imagery is extremely useful for change detection and monitoring efforts, it presents a number of disadvantages. For example, it is difficult to obtain an image over the area of interest during the desired timeframe. The revisit of the satellites, as well as the presence of cloud cover, limits the availability of data. The limitation is critical when data are needed in a very specific timeframe; particularly, when imagery needs to coincide with field data collection.

In this study, medium and high resolution satellite data for the area are not available at the National Remote Sensing Centre of Mauritius. Therefore, Microsoft Virtual Earth cloud free image dated March 2004 for the region is used in the evaluation of wetland losses and encroachments. It has been geometrically corrected and georeferenced by using the large scale topographic map of the area (Figure 5).

Figure 5 – Satellite Imagery 2004 of the study area (Microsoft Virtual Earth)

(34)

3.2.4 Ground surveys for boundary delineation

According to Olorunfemi (1983 cited Zubair, 2006), conventional ground methods of land use mapping are labour intensive and time consuming. Maps produced are not frequent and soon become obsolete, particularly in a rapid changing environment. Moreover, the monitoring of changes and time series analysis is difficult with traditional method of surveying when compared with satellite remote sensing techniques which detect changes at regular intervals of time.

However, field surveys and ground truthing is performed for the verification of boundary limits so as to clear uncertainties of wetland alterations during interpretation of aerial photographs. Due to private property access restrictions at certain areas, data on the delimitation of wetland boundaries have been gathered from ground survey at some accessible regions only. Actual wetland limits at these regions are measured using Geographic Positioning System (GPS) of sub-metre accuracy.

3.3 Rationale behind data for assessment

As the population growth and development pressure continue to affect the ecological integrity of wetlands in Grand Baie, the changing situation and land use practices occurring there require contemporary information about the extent and location of wetland for sound management. Since most historical wetlands data for Grand Baie are captured from old aerial photographs, they are compared with the most recent ones. The digital databases are updated to show the continuing development and land use changes.

Due to the potentially important influence of wetland surroundings on wetland health, digital data are compiled and analyzed for a wider zone surrounding each wetland including the wetland’s contributing area. The contributing area is the geographic area that contributes water to a wetland whereas the surrounding area is the area around the wetland.

Therefore, the collection of data needs to cover areas that influence wetland’s health farther away. These distant alterations occurring in the contributing area are mostly caused by human induced activities like roads construction, buildings and converted agricultural lands.

(35)

3.4 GIS tools for monitoring and management of wetlands

GIS technology has made it possible to effectively identify, assess and monitor wetlands loss faster than the conventional methods. It provides easy access to large volumes of data and has a variety of analysis tools for assessing areas of rapid change. As the basic requirements for the formulation of policies depend on informed decision making, ready access to appropriate reliable and timely data in suitable GIS form is necessary. The GIS component is a key aspect for the inventory and mapping of wetland for it will provide the necessary datasets in the monitoring and management process.

The GIS software used for this study is ESRI’s ArcGIS 9.2 with Spatial Analyst extension.

This software provides an excellent means for visualising and analysing data. It allows discovering patterns, relationships and trends in data that are not apparent in databases, spreadsheets and statistics. It is powerful in managing and integrating data, performing advanced analysis, modelling and displaying results on maps. As such it is a perfect tool to analyse historical, current and future wetland data.

This software also aids in the interpretation of information within or near wetland buffer zones and demonstrates its usefulness for wetland evaluation. GIS layering and analysis help to identify wetland loss in a timely and objective manner. The software addresses the spatial and temporal changes and guides decision-making in providing such information to answer spatial queries like:-

a. Where are the wetlands located?

b. Where are wetlands being lost or reduced?

c. How quickly are wetlands being destroyed?

d. What are the extents of remaining wetlands?

e. Which sites are of priority for close monitoring?

3.5 Methods for collecting land use and land cover data

The methodology to reconstruct the past land cover to compare with the current land use pattern outlined hereunder covers three major tasks namely: (i) compilation of all available spatial data layers that contribute to make an inventory of wetland for assessment, (ii) interpretation of aerial photographs and satellite imagery to identify obvious changes to wetlands during two time periods (1967-1991 and 1991-2004) and (iii) using GIS analysis tools to detect changes in wetland areas.

(36)

These tasks consist of several procedures for compiling and entering existing spatial data into a GIS, including:

 scanning of aerial photographs, interpreting and digitising,

 georeferencing of data from existing digital basemaps,

 image data input and conversion to GIS format,

 creation of a geodatabase, and

 direct data entry including global positioning systems (GPS).

A digital spatial database for the “historic” land cover of the study area is first established from aerial photographs taken in 1967, depicting the region’s past physical characteristics.

Black and white aerial photographs archived at the Ministry of Housing and Lands have been used to create such spatial database. These data are considered as the timeline for this study. It is deemed that 1967 is a good baseline as it is considered to be the pre- backfilling period, when the island’s economic development was at its early stages. The photograph is scanned and the land use classification is interpreted and vectorised from the raster datasets. The interpretation and mapping of land use is complemented with appropriate ground truthing. Such quality control checks are performed to prevent false changes from being recorded and to provide confirmation of the photo interpretation work.

Prior to the extraction of information from aerial photographs, the image patterns of the various features must be carefully identified through photo-interpretation i.e. tone, texture, shape, size, shadow. Uncertainties during this process are closely examined under a mirror stereoscope using overlap of pair photographs to ascertain accurate wetland boundaries, vegetation boundaries, built-up areas, etc. Scanned photographs are geo-referenced, rectified, and the photo-interpreted signature delineating the cover types are digitized on- screen using ArcGIS 9.2 software (Figure 6).

(37)

Figure 6 – Georeferencing of the study area Image using ArcGIS 9.2

The purpose of digitising features from scanned photographs is to transform information about land cover from analogue format into digital vector format. The on-screen digitising is an interactive process using the referenced image as a backdrop. This method of capturing digital data is also known as "heads-up" digitising as the attention is focused on the screen of the computer to create required layers with the click of the mouse.

Based on the priori knowledge from old maps and the reconnaissance survey of the site, land cover types digitized from aerial photographs 1967 and 1991 and satellite imagery 2004 have been classified into main categories and coded accordingly (Table 2).

CODE LAND USE/LAND COVER CATEGORIES

REMARKS

1 Wetland Wetlands with and without water

2 Built up Settlements incl. recreational and commercial facilities 3 Sugar cane Agricultural land under sugar cane plantation Including

pile of stones

4 Vegetation Incl. native, invasive plants, scrub lands, bushes, trees and dry grasses near and around wetlands

5 Sand Area along the shoreline

6 Sea Coastline separating land and sea

Table 2 – Land Use/Land Cover classification of the area of study

GIS for Effective Wetland Monitoring in the North of Mauritius

Master Thesis

submitted within the UNIGIS MSc. programme at the Centre for Geoinformatics (Z_GIS)

Salzburg University, Austria

under the provisions of UNIGIS joint study programme with Goa University, India

GIS for Effective Wetland Monitoring in the North of Mauritius

by

Farook Nathire

Port Louis, Mauritius, 23 December 2008

Science Pledge

Acknowledgements

Abstract

Table of Contents

List of figures

List of tables

CHAPTER ONE

1.1 Introduction

1.2 Background and status of wetlands in the North of Mauritius

1.3 Study area (part of Grand Baie village)

1.4 Problem statement

1.5 Aims and objectives

CHAPTER TWO

Literature review

2.1 Introduction

2.2 Definitions of wetland

2.3 Physical characteristics of wetlands

2.4 Ramsar Convention on wetlands

2.4.1 Framework for wetland inventory, assessment and monitoring

2.5 Geographic Information System (GIS)

2.6 GIS in effective wetland management

2.7 Change detection using GIS tools

2.8 GIS for Wetlands Health Assessment

2.9 GIS in assessing areas of rapid wetland change

2.10 Remote sensing in wetland change detection

2.11 GIS in prediction of land use change

2.12 GIS in planning wetland restoration

2.13 Analysis in planning methodology

CHAPTER THREE

Methodology

3.1 Introduction

3.2 Spatial data acquisition

3.2.1 Aerial photographs

3.2.2 Digital maps

3.2.3 Satellite imagery

3.2.4 Ground surveys for boundary delineation

3.3 Rationale behind data for assessment

3.4 GIS tools for monitoring and management of wetlands

3.5 Methods for collecting land use and land cover data