4th Intake (2017/2018) Flood Risk Analysis in Rathnapura District for Disaster Management Semester I (PBL Resubmission) Remote Sensing and Geographic Information Systems (GIS) for Planning and Management- (CE5804) Lecturer in Charge: Sr. Prof. NTS Wijesekeara Index No:179230P Rohit Adhikari M.Sc./ PG. Diploma in Water Resources Engineering and Management UNESCO Madanjeet Singh Centre for South Asia Water Management Department of Civil Engineering University of Moratuwa Email Address:
[email protected] Place of Employment: APECS Consultancy, Bhutan Date of Submission: 03rd November 2017 Table of Contents 1. Title: .................................................................................................... Error! Bookmark not defined. 2. Introduction ........................................................................................................................................... 4 3. Problem Statement ................................................................................................................................ 6 4. Selection of a Solution to the Problem.................................................................................................. 6 4.1 Identification of alternative solutions ............................................................................... 6 4.2 Selection of Solution .......................................................Error! Bookmark not defined. 5. Objectives ............................................................................................................................................. 8 5.1 Overall Objective ............................................................Error! Bookmark not defined. 5.2 Specific Objectives ........................................................................................................... 8 6. Methodology ....................................................................................................................................... 10 7. Literature Review................................................................................................................................ 10 7.1 Rationale for Criteria .......................................................Error! Bookmark not defined. 8. Field Work and Data Summary .......................................................................................................... 14 8.1 Project Area-Rathnapura District ................................................................................... 14 8.2 Data Requirement ........................................................................................................... 15 9. Analysis and Specimen Computations ................................................................................................ 16 9.1 Objective Function ......................................................................................................... 16 9.2 GIS Vector Overlay Flowchart ...................................................................................... 16 9.3 Classification .................................................................................................................. 22 9.4 Attribute Table Operation .............................................................................................. 23 9.5 Data Layers .....................................................................Error! Bookmark not defined. 10. Results and Summary ..................................................................................................................... 26 11. Discussion and Conclusion ............................................................................................................. 33 12. Achievements of Learning Outcomes ............................................................................................. 34 13. Personal Comment on PBL ............................................................................................................. 34 List of Figures Figure 1: Methodology Flow Chart .............................................................................................. 10 Figure 2: Project Location ............................................................................................................ 14 Figure 3: GIS Vector Overlay Chart ............................................................................................. 16 Figure 4: Tools for Application .................................................................................................... 17 Figure 5: Rainfall Class ................................................................................................................ 18 Figure 6: Landuse Class ................................................................................................................ 19 Figure 7: Elevation Class .............................................................................................................. 20 Figure 8: Slope Class .................................................................................................................... 21 Figure 9: River Buffering for Proximity ....................................................................................... 22 Figure 10: SQL Operation ............................................................................................................ 24 Figure 11: Union of Rainfall and Landuse ................................................................................... 26 Figure 12: Union of Elevation and Slope ..................................................................................... 27 Figure 13: Union of Rainfall, Landuse, Elevation and Slope ....................................................... 28 Figure 14: Final Hazard Map ........................................................................................................ 29 Figure 15: Priority In DSD Context .............................................................................................. 30 List of Tables Table 1: List of Literture Reviewed .............................................................................................. 11 Table 2:Criteria Selection ............................................................................................................. 11 Table 3: Data Requirements.......................................................................................................... 15 Table 4: Landuse Classification .................................................................................................... 18 Table 5: General Classification ..................................................................................................... 22 Table 6: Classification for Elevation-Slope Union ....................................................................... 22 Table 7:Data Layer Types and Preparation .................................................................................. 25 1. Introduction 1.1 A clear explicit indication of the main theme/water sub sector corresponding the addressed problem Flood is a major natural hazard with often immeasurable impact, affecting annually 170 million people (Kowalzig, 2008). Sri Lanka has experienced some of the worst flood situations in the past two decades. The recent floods and landslide of May 2017 resulted over 200 deaths and affecting over 7 million people. 1.2 Importance of solving the problem and to which part of the national interest would be fulfilled Indisputably, strategies against floods’ impact at a region scale require the identification of prone areas (Tehrany et al., 2013) to provide early warning, facilitate quick response and decrease the impact of possible flood events (Kia et al., 2011 ). The most effective way of reducing the risk to people and property is through the production of flood risk maps. Most countries have produced maps which show areas prone to flooding based on flood data. Flood Hazard Mapping is a vital component for appropriate land use planning in flood- prone areas. It creates easily-read, rapidly-accessible charts and maps which facilitate the identification of areas at risk of flooding and also helps prioritise mitigation and response efforts (Bapulu & Sinha, 2005). Flood hazard maps are designed to increase awareness of the likelihood of flooding among the public, local authorities and other organisations. They also encourage people living and working in flood-prone areas to find out more about the local flood risk and to take appropriate action (Environment Agency, 2010). For Sri Lanka, a developing country in South Asia, efficiently managing economy and distribution of resources, both preventive measures and relief materials will be very meaningful with such maps. 1.3 Indicate methods incorporated to identify the criticalness and importance of the identified problem According to the Disaster Management Centre, this year’s’ flooding is believed to have been the worst since the great flood of 2003 where over 10,000 homes were destroyed. As reported in the newspaper Sunday Observer dated 28th May 2017, Ratnapura, Galle, Matara and Hambantota districts are the worst affected with the Ratnapura town completely inundated by flood waters. Rathnapura has recorded sever flood problems annually and during severe flood situations in Sri Lanka. Based on the website http://flo o dlist.com, which rep orts flood incidents the death tool as recorded on the same day was 146 (71 in Ratnapura, 43 in Kalutara, 14 in Matara, 8 in Galle, 5 in Hambantota, 3 in Gampaha, 2 in Kegalle). Notablythe highest was in Rathnapura. 1.4 Explanation of the overall problem or part of the problem addressed by the present problem based learning projects The main problem from engineering aspect is the increase in the water levels of Kelani Ganga which runs through Rathnapura District. From disaster management aspect, it is the lack of proactive forecasting, improper settlement along river banks and lack of infrastructure such as levees and bunds, retention/detention ponds to safely discharge the streamflow. The ultimate solution will be to construct engineering structures or relocating families that are most prone to be affected. However, this requires huge financing and would not be feasible to go on a single phase. Thus, a priority order has to be developed for carrying out disaster management activities. In this context preparation of a flood hazard map will serve as a basis for planners to set priorities for implementation of mitigation measures. 1.5 Evidence to convince that your efforts are not a repetition of the an already done work Although floods are the most frequent natural disasters in Sri Lanka they had received little attention until the tsunami of December 2004. After the Tsunami, however, disaster management strategies underwent rapid changes and under this framework flood hazard mapping has, particularly, been realized as one of the foremost tasks to be accomplished in support of disaster management activities. (Fowze, 2014). There have been studies to hydro-dynamically model the lower reaches of Colombo, and frequently flood inundation maps are produced just before an anticipated flood event, a proactive flood risk maps for Rathnapura were not found. 1.6 Indication of the uniqueness of your work Although flood risk mapping is not a very new subject to engineers and planners, its efficient and rigorous use in Sri Lankan context is still at infancy. This map will serve a tool for the planners in Rathnapura district for flood planning which is new. There were no contents of literature review and basic internet search about preparation of such map for Rathnapura District which is a crucial flood prone area. Thus this work is unique 2. Problem Statement Which areas in Rathnapura District must be prioritized for flood disaster management activities? 3. Selection of a Solution to the Problem 3.1 List of alternatives considered as the most appropriate solutions Flood management aims to reduce the frequency and magnitude of flooding in order to limit the damage. The flowing are the broadly acceptable options available for flood management; i. Hard engineering defenses ii. Soft engineering defenses 3.2 Rationalization of each alternative with clear indication of advantages, importance The aim of flood management is to protect homes, businesses and the environment from flooding; • Hard Engineering Defenses: involves the use of technology to control rivers - building structures that reduce flooding. The activities include construction of dams and reservoirs, levees, dredging the channel, straightening rivers. • Soft Engineering Defenses: involves floodplain management, wetland conservation, river restoration, flood mapping and forecasting 1. Hard engineering defences involve the use of technology to control rivers - building structures that reduce flooding: Dams and reservoirs - designed to store water and therefore control the discharge of the river. Levees - increases the height of the river banks and therefore the river can contain more water Dredging the channel – keeps the channel free from sediment so more water can flow through it. Straightening rivers - increases the speed of the river to remove water from affected areas. Overflow channels which allow rivers to flood areas of unused land or areas which do not cause much damage. Building flood walls Hard engineering approaches tend to give immediate results and control the river but are expensive General disadvantages of engineering defences Expensive to build and maintain, need technical skill Floods happen less often – but when they do occur they tend to be more hazardous … imagine if a dam fails Natural processes are disrupted – crops don’t get fertile silt Ugly structures 2. Soft Strategies Flood Warning Systems - This enables people time to remove possessions and evacuate areas. Sandbagging - This attempts to flood proof homes and buildings as a last resort. Insurance - This spreads the cost of the flood damage. Flood Plain Zoning - This tries to organise the flood defences in such a way that land that is near the river and often floods is not built on. This could be used for farming. The areas that rarely get flooded therefore would be used for houses, transport and industry. Advantages They are cheaper to maintain than built structures Flooding is more predictable reducing the risk of an unexpected disaster They can improve opportunities for recreation such as fishing They are more attractive to look at. More sustainable Does not interfere directly with the river’s flow 3.3 Selection Criteria for alternatives and rationalization (references) for the marking criteria. The following criteria is used to evaluate the alternatives; i. Cost: For any project or activity cost is an important aspect for consideration. Usually it is also the single most predominant factor for selecting a solution for a problem. ii. Time: Time is another crucial factor. However, it is dependent upon the scale and scope of a solution. Bigger solutions requiring physical construction require more time, however desktop studies require substantially less time to accomplish. It is also a factor for consideration when it comes to planning stage, the latter being a more opted choice. iii. 3.4 Evaluation marks and marking scheme used for the selection of solution with justification A marking scheme of a scale from 1-5 is given for both the criteria. 1 Indicates that it is requires the most cost and time and 5 indicates the inverse. Approach Time Cost Hard Engineering 1 1 Soft Engineering 5 5 3.5 Identified Selection and associated computation of aggregate mark for the alternative. Soft engineering defences are far less expensive but it is the hard engineering that is effective and assures water supply, economic growth and stability in long term. To balance these, components of both must be coupled in order to achieve effective results. Based on the above rationale, the solution chosen for the particular problem is to firstly prioritize the flood hazard areas which would then help planners to prepare a course of plan. Such a prioritization can be can be carried out without much expenses using modern GIS application 4. Objectives 4.1 The indication of Project Outcome Flood risk mapping in Rathnapura District for Disaster Management planning. 4.2 Specific Objectives 1. Situation analysis and literature survey 2. Determination of Parameters 3. Identify spatial variation of Flood Hazard using GIS. 4. Results and discussion. 4.3 Outputs for each specific objective 1. Situation analysis and literature survey Literature Review on techniques for flood risk mapping 2. Determination of parameters Literature Review on parameters used for mapping Develop objective function 3. Identify spatial variation of Flood Hazard using GIS Develop overlay operation flowchart Perform GIS operations in ArcGIS 4. Results and discussion. Identify the flood risk Giving conclusion and recommendations 6. Methodology Figure 1: Methodology Flow Chart 7. Literature Review 7.1 Literature used to support the techniques used No exact agreement exists on which factors should be applied in flood susceptibility assessments (Tehrany et al. 2014). However, some of the variables are mostly used by numerous researchers which indicate their important role in flood mapping. On the other hand, recent studies have aimed to present models that use the least number of independent parameters while s till achieving highly accurate results (Campolo et al. 2003). The following literature were referred to determine the criteria. Table 1: List of Literture Reviewed 7.2 Literature used to support the Parameters Based on the above literature and their relative use in the literature as detailed below the following parameters were selected for analysis; Table 2:Criteria Selection Sl.No Criteria Literature Remarks 1 Rainfall [1][3][4][5][6][7] Selected 2 Elevation [1][2][3][4][5][6][7] Selected 3 Slope [1][2][3][4][5][6][7] Selected 4 Landuse [1][2][3][5][6][7] Selected 5 Proximity to River [1][3][4][5][6][7] Selected 6 Flow Accumulation [5] Not Selected 7 Geology [7] Not Selected 7.3 Literature used to support the indicators used for evaluation 1. Rainfall: Heavy rainfalls are one of the major causes of floods. Flooding occurs most commonly from heavy rainfall when natural watercourses do not have the capacity to convey excess water. Floods are associated with extremes in rainfall, any water that cannot immediately seep into the ground flows down slope as runoff. The amount of runoff is related to the amount of rain a region experiences. The level of water in rivers or lakes rises due to heavy rainfalls. When the level of water rises above the river banks or dams, the water starts overflowing, hence causing river based floods. The water overflows to the areas adjoining to the rivers, lakes or dams, causing floods or deluge. (Yashon O. Ouma, 2014). 2. Elevation: The altitude has significant impact on the spread of flooding in the study area. Also, this parameter has a key role in the control of the overflow direction movement and in the depth of the flood (Stieglitz et al. 1997). 3. River Proximity: The distance from river factor plays an important role in determining the flooding area. According to previous studies (Fernandez and Lutz 2010), the most affected areas during floods are those near the rivers, as a consequence of overflow 4. Slope: The slope percent can be considered as surface indicator for identification of flood susceptibility (Youssef et al. 2011). In other words, this factor must be included, since it plays an important role in determining surface runoff velocity and vertical percolation, and thus affecting flood susceptibility 5. Landuse/Landcover: The land-use and land-cover management of an area is also one of the primary concerns in flood hazard mapping because this is one factor which not only reflects the current use of the land, pattern and type of its use but also the importance of its use in relation to soil stability and infiltration. Land-cover like vegetation cover of soils, whether that is permanent grassland or the cover of other crops, has an important impact on the ability of the soil to act as a water store. Runoff of rainwater is much more likely on bare fields than those with a good crop cover. The presence of thick vegetative cover slows the journey of water from sky to soil and reduces the amount of runoff. On the other hand, impermeable surfaces such as concrete, absorbs almost no water at all. Land-use like buildings, roads, slum areas, decreases penetration capacity of the soil and increases the water runoff. In other words, land-use types work as resistant covers and decrease the water hold up time; and typically, it increases the peak discharge of water that enhances a fastidious flooding. This implies that land-use and land-cover are crucial factors in determining the probabilities of flood happenings. (Yashon O. Ouma, 2014). 8. Field Work and Data Summary 8.1 Project Area-Rathnapura District Figure 2: Project Location 8.2 Data Requirement Table 3: Data Requirements Data Layer Layer Type Spatial Resolution Data Availability/Accessibility Rainfall Table Daily Monthly rainfall from Meteorology Department Project Area Polygon 1:50000, DSD 1:50000 digital data layers - Survey Department (available and accessible) DSD Polygon 1:50000, DSD 1:50000 digital data layers - Survey Department (available and accessible) GND Polygon 1:50000, DSD 1:50000 digital data layers - Survey Department (available and accessible) Landuse Polygon 1:50000 1:50000 digital data layers - Survey Department (available and accessible) Streams Polyline 1:50000 1:50000 digital data layers - Survey Department (available and accessible) Slope Polygon 30m Srilanka DEM- USGS Elevation Polygon 30m Srilanka DEM- USGS 9. Analysis and Specimen Computations 9.1 Statements/descriptions in a rational order for problem solving using analytical capability Objective Function Main Objective Function: Flood Risk Analysis in Rathnapura District - f(Flood Risk Analysis) Sub Objective Functions : f(Risk)-f(Rainfall, Elevation, Slope, Landuse, Proximity to River) Based on the literature discussed in Section 7 under Literature Review, it was found that the above factors are most important considerations by most literature and thus the same is incorporated here. GIS Vector Overlay Flowchart Figure 3: GIS Vector Overlay Chart In methodology all the layers were prepared for 3 classes. All base data layers were clipped from the boundary of project area before use any operation. Figure 4: Tools for Application 9.2 Demonstrating that the analysis work in this report is worthy engineering computations Rainfall Annual Daily Maximum Rainfall data from period of 1999-2011 was table was added to ArcMap using Excel to table to convert table data to points. The station location co- ordinates were given as latitudes and longitudes in a table. Loaded table locations were generated on the map using display XY. Once generated the points, rainfall distribution was taken using Thiessen polygon. Rainfall varied between 204 and 402.9. Thus based on linear distribution three classes were specified as; Low <270 mm Medium 270-340 mm High >340 mm Page | 17 Figure 5: Rainfall Class Landuse The details of the land use were converted to three classes as below on the basis of similar work by authors. Primarily the concern was to separate areas based on permeability with respect to vegetation; Table 4: Landuse Classification Sl.No GFCODE Abbreviation Classification Remarks 1 BLTPA Built up area High Impermeable 2 CHNLA Irrigation Channel High Impermeable 3 CMTYA Cemetery High Impermeable 4 ROCKA Rock High Impermeable 5 STRMA Stream (LINE/AREA) High Impermeable 6 TANKA Tank boundaries High Impermeable 7 CHNAA Channel (Abandoned) Medium Semi-permeable 8 ILINA Island Medium Semi-permeable 9 MRSHA Marsh Medium Semi-permeable 10 TNKAA Tank (abandoned) Medium Semi-permeable boundaries 11 CCNTA Coconut Low Permeable 12 CHENA Chena Low Permeable 13 FRSUA Forest - Unclassified Low Permeable 14 GRSLA Grassland Low Permeable 15 HOMSA Homesteads/Garden Low Permeable Page | 18 16 OTHRA Other cultivation Low Permeable 17 RBBRA Rubber Low Permeable 18 SCRBA Scrub land Low Permeable 19 TEAA Tea Low Permeable Figure 6: Landuse Class Elevation and Slope Were used primarily from 30-m DEM from USGS. However, for application, the raster images were not used. Slope Map was created from the DEM file and both DEM(for elevation) and Slope Map were reclassified before converting the raster images to vector polygon. For classification, reference was made to the literature. However there is not standard methodology for classification. (Omid Rahmati 2015) has classified under five classes for a data with a range of 1700- 1775 m. (Sailesh Samanta 2016) has classified under nine classes of data ranging from 20->500. (Yashon O. Ouma 2014) has made five classification of data ranging from 1924-2223m. Also for slope five classes were made for data ranging from 0-90 degrees. However, an evident classification strategy applied by all was the use of linear distribution. The total range was divided equally among the classes. Thus, for this work Elevation and Slope has been classified as; Elevation Page | 19 Low <700m Medium 700-1400 High >1400 Figure 7: Elevation Class Slope Low <30 Medium 30-60 High >60 Page | 20 Figure 8: Slope Class River Proximity Was determined using the Buffer tool. (Omid Rahmati, 2015) – 100 to 500 in 5 classes while Sailesh Samanta2016 used 9 classes to classify 100-2000 m. (Ioannis Kougias 2015) wrote ‘It appears that areas near the river network (>200 m) are highly flood hazard, whereas the effect of this parameter decreases in distances <2000 m. For this work considering the Srilankan flood plains and the flat terrain; River Proximity Low <1000 Medium 500-1000 High >500 Page | 21 Figure 9: River Buffering for Proximity Classification All layers were analyzed for 3 classes and classification was done by overlaying two layers at a time. Re-classification after overlaying was done using the Table below. Table 5: General Classification H M L H H H M M H M L L M L L However, the reclassification between Elevation and Slope was done in accordance to the following. This is as explained by Ioannis Kougias, 2015 ‘Water flows from higher to lower elevations and therefore slope influences the amount of surface runoff and in filtration. Flat areas in low elevation may flood quicker than areas in higher elevation with a steeper slope.’ Table 6: Classification for Elevation-Slope Union H M L H L L M M L M H L M H H Page | 22 Color code for 3 classes Color Classification High Medium Low Attribute Table Operation Add field Add field allows the user to add more information to the data layer. There are several types of data can be stored in new field such as text, numbers, etc. The data type of the information required to store can be decided prior to add field and set the type according to that. Select by Attributes The Select by Attributes dialog box helps to define one or more criteria of the SQL expression that can consist of attributes, operators, and calculations. It allows user to handle bundle of data records at once for a particular operation. In this PBL, select by attributes option was done a major role where necessary in classifications. Figure below shows the sample SQL query statement for classification of ‘High’ class in for a Union between Rainfall-Landuse and Elevvation-Slope.. Once the query statement was completed it needs to be verified before executing it. Successfully verified statement will select records as commanded in the query. Page | 23 Figure 10: SQL Operation Field calculator Field calculator is one of the most important attribute operations. Using this operation, mathematical operations using information in two fields can be easily done for selected records. Other than mathematical operations this option allows to add different information easily in to the database. All the above table operations with other table operations, the complex analysis can be easily managed in short time period. These operations were very helpful to find meaningful solution in this PBL Page | 24 9.3 A summary of Methods, tools and techniques taught in the associated teaching module and used in the Analysis Table 7:Data Layer Types and Preparation Sl.No Data Layer Layer Type Layer Preparation 1 Rainfall Table Excel to Table to add in to Arcmap Display XY to generate points at rainfall stations Clip to select the area within the boundary Thiessen Polygon to convert to rainfall distribution polygon Project Area Polygon Digitizing the boundary DSD Polygon Clip to select the area within the boundary Landuse Polygon Clip to select the area within the boundary Export data by selecting various land uses into three categories of Permeable, Impermeable and Semi-permeable Classifying landuse class by querying using select by attributes and Field calculator Stream Polyline Clip to select the area within the boundary Multiple ring buffer to classification Classifying river proximity class by querying using select by attributes and Field calculator Slope Map Polygon Clip the DEM to select the area within the boundary Perform Slope Analysis Reclassify Raster Covert Raster to Polygon Classify slope map by querying using select by attributes and Field calculator Elevation Map Polygon Clip the DEM to select the area within the boundary Reclassify Raster Covert Raster to Polygon Classify elevation map by querying using select by attributes and Field calculator Page | 25 10.Results and Summary Figure 11: Union of Rainfall and Landuse Page | 26 Figure 12: Union of Elevation and Slope Page | 27 Figure 13: Union of Rainfall, Landuse, Elevation and Slope Page | 28 Figure 14: Final Hazard Map Page | 29 Figure 15: Priority In DSD Context Flood Index = [3 x (High Risk area) + 2 x (Medium Risk area) + 1 x (Low Risk area)]/ DSD Area Index is based on DSD area, therefore 5 major DS Divisions were considered for prioritization. Page | 30 10.1 A summary table describing main results achieved when reaching the target solution Sl.No Main Results achieved Remarks Generation of Thiesen Rainfall Class Map Figure 5 Generation of Landuse Class Map Figure 6 Generation of Elevation Class Map Figure 7 Generation of Slope Class Map Figure 8 Generation of River Buffering for Proximity Map Figure 9 Union of Rainfall and Landuse Figure 11 Union of Elevation and Slope Figure 12 Union of Rainfall, Landuse, Elevation and Slope Figure 13 Final Hazard Map Figure 14 Flood Index [3 x (High Risk area) + 2 x (Medium Risk area) + 1 x (Low Risk area)]/ DSD Area Map for Priority In DSD Context Figure 15 Flood Risk Prioritization DSD Wise Nivithigala Ayagama Imbulpe Kollana Kalawana Page | 31 10.2 A Summary table connecting the specific objectives and associated outputs mentioned in the objectives section. No Objective/Specific Objective Output/Outcome Achieved Results 1 Flood risk mapping in Disaster Preparedness and Flood Risk Map which can be Rathnapura District for Management (Outcome) used for future disaster Disaster Management management planning planning. (Overall Objective) 2 Identification of factors for Development of GIS f(Flood Risk Analysis) flood risk map based model for the f(Risk)-f(Rainfall, Elevation, Rathnapura District Slope, Landuse, Proximity to River) 3 Develop a conceptual model GIS vector overlay Methodology flow Chart of GIS and methodology flow chart operations achieving vector overlay operations identification of flood risk areas 4 Prepare vector data layers GIS overlay operations District Boundary of Rathnapura District Divisional Secretariat Divisions of Study area Annual average rainfall distribution of Study area Thiessen Polygon to convert to rainfall distribution polygon Stream network polyline data layer of Study area Buffering of Stream Network Classified Land Use polygon data layer of Study area Preparation of Elevation Map and its associated classes Preparation of Slope Map and its associated classes Page | 32 Flood Risk locations of Study area DSD wise priority mapping 5 Produce flood risk map Identification of Prioritized DSD wise top 5 risk prioritize area for future area map for Rathnapura District planning 11. Discussion and Conclusion Remote sensing and GIS technique has successfully established its application in following areas of flood management such as flood inundation mapping, floodplain zoning and river morphological studies. Flood mapping during the flooding and flood plain mapping after the flood recedes is essential. The flood hazard map can give planners, insurers and emergency services a valuable tool for assessing flood risk. Each of them needs to assess risk for more than one scenario. 11.1 An itemized list of issues faced and methods used to overcome those Determination of Criteria: Since different literature have used different parameters it was an issue to s elect parameter based only on a particular literature. Thus, a wide variety of papers from different reputed journal sources and of a time frame from 2014- 2016 were used to select the parameter and assign the initial values. 11.2 A list of Assumptions with respect to data That the 30 meter Digital Elevation Mo del is fairly accurate. That the stream network and land use pattern as digitized by Department of Survey has not changed. 11.3 A list of Assumptions made during the computation of solution 11.4 A clear indication of the acceptability of the assumptions made The use of the 30-m DEM to compute the elevation and slope has also been used in many other authors from the literature reviewed such as (Samanta S. 2016 and Kougias I.2015) and thus it is an acceptable approach in such studies. In the absence of a more recent data from Department of Survey, the land use and stream network are acceptable to be used for such flood hazard mapping 11.5 A section with a discussion on how this work can be improved for better application The work can be enhanced by field verification and ground truthing. In several areas the flood plain might be wide but there could also be areas where the flood plain will not extend beyond 100 meters. Such considerations will have to be made and then further Page | 33 decision taken before completely relying on a desktop analysis. An example is that because recent flood reports indicated the most affected district to be Rathnapura, Elapatha and Kuruwita against the ones obtained in this result. 11.6 Itemized list of conclusions 1. GIS is a very powerful tool and the application of GIS using only the vector data is as powerful as its application using raster data. 2. Criteria selected for this study were Rainfall, Elevation, and Proximity to River, Slope and Landuse. 3. Nivithigala, Ayagam, Imbulpe, Kolnna, Kalawana are the most important areas for focus. 12. Achievements of Learning Outcomes 1. Identification and understanding of the Capability of Geographic Information System (GIS). 2. Learning of Concepts, components, capabilities, advantages, data structures related with GIS. 3. Learning of Data Types as Raster, Vector, Topology, data quality, database management 4. Learning the mapping as maps and mapping, map projection and coordinate system. 5. Understanding of the theoretical and practical knowledge of geographic information system and remote sensing. 6. Prepare, manipulate, display and analyze spatial data for planning and management. 7. Development of objective functions. 8. Data layer manipulations. 9. Identification of mathematical functions when overlaying data layers. 10. Analytical skills in classifications. 11. Multi layer and single layer operations. 12. Converting coordinate systems, geo referencing, symbology representations etc. 13. Potential and use of GIS software for sustainable spatial planning and management applications 14. GIS operations for sustainable water related project. 15. Personal Comment on PBL This PBL has given me an opportunity to handle professional GIS work using only vector data. Even though some data were not available in vector format I had the opportunity to learn to convert raster data and use them. Student’s Responsibilities A student should discuss with the supervisor right from the start of the PBL about topic Page | 34 selection and literature review and make timely visits to assure that the meth ds followed are in line with the standard approach for GIS application. Additional input in the Course Despite acknowledging a strong support from the course management, as a comment, the course could make a sample of the standard PBLs to be used as a reference and a session could be arranged right in the start of the semester to give a detailed approach ab out how each one the sub section should be filled. Also there is a need to validate if all the sub sections as outlined in the guidelines are applicable to all PBLs. 11) Flood hazard mapping in lower reach of Kelani River, Sri Lanka. Available from: https://www.researchgate.net/publication/228772034_Flood_hazard_mapping_in_lower_reach_o f_Kelani_River_Sri_Lanka [accessed Nov 01 2017]. Page | 35