Coastal Erosion Project Diani Beach, Kenya May – June 2006 Supervisors Prof. dr. ir. M.J.F. Stive Dr. ir. J. van de Graaff Ir. H.J. Verhagen Jochem Ballot│ Claartje Hoyng │ Inge Kateman │Michiel Smits│Renske de Winter General notice to the reader: In the academic programme for Hydraulic Engineering we have in the 4th year (i.e. in the first year of the Master Programme) the requirement that students should do in a group of four to six persons a so-called "groupwork". It is also called "Master Project". During this groupwork they should make a full design of something. The work should be integral, starting with terms of reference, and ending with the real design. This can be a structure, but also it can be a harbour lay-out, a policy plan design, etc. The total time available for the project is in the order of two months and will provide 10 European Credits. It has to be practical and applied. It is certainly not an M.Sc. thesis assignment (the thesis work is individual, 6 months and more focussed on research or advanced design work on details). But it is also not an appren- ticeship, internship or traineeship where the student has to work together with a group of experienced people. For this groupwork they have to solve the problem on their own (of course with guidance). This report is the result of such a Master Project. This report has been assessed by staff of TU Delft. It has been provided with a passing mark (i.e. a mark between 6 and 10 on a scale of 10), and consequently considered sufficient for publication. However, this work has not been fully corrected by TU Delft staff and therefore should be considered as a product made in the framework of education, and not as a consultancy report made by TU Delft. The opinions presented in this report are neither the opinions of TU Delft, neither of the other sponsoring organisations. Department of Hydraulic Engineering Delft University of Technology Coastal Erosion Project Kenya Coastal Erosion Project Diani Beach, Kenya May – June 2006 1 Coastal Erosion Project Kenya 2 Coastal Erosion Project Kenya Preface As a part of the master-course Hydraulic Engineering & Fluid Mechanics, at the Civil Engineering faculty of the Delft University of Technology, a master project about coastal erosion problems along the Kenyan Coast is carried out. This project is done by 5 students, all specialising in the direction of Coastal Engineering. The research in Kenya is focused on Diani Beach, south of Mombasa. In Delft we worked for several weeks on the workplan, sponsoring and other preparations. This was followed by a stay of nine weeks at the location of our project, namely Mombasa and Diani Beach in Kenya. We concluded this period with two presentations, one for governmental organisations together as ICAM (Integrated Coastal Area Management), and the other for the Kenyan Association of Hotelkeepers and Caterers. Afterwards a few weeks were spent to finish the report and to give four presentations to our teachers and Dutch sponsors. We would like to thank our teachers for their comments and advices: Prof. dr. ir. M.J.F. Stive Dr. ir. J. van de Graaff Ir. H.J. Verhagen Also gratitude goes out to our sponsors, who made the project financially possible: Van Oord N.V. Boskalis Westminster B.V. Royal Haskoning IHC Holland Merwede B.V. Alkyon Hydraulic Consultancy and Research B.V. We owe much gratitude to Mr. Wainaina Mburu from the Coast Development Authority and Mrs. Saada Khamis from the Kenya Association of Hotelkeepers and Caterers. They helped us very much with our housing in Kenya and getting us in contact with all the people involved in the coastal erosion problems along the Kenyan Coast. Project Group CF 57 Jochem Ballot Claartje Hoyng Inge Kateman Michiel Smits Renske de Winter 3 Coastal Erosion Project Kenya 4 Coastal Erosion Project Kenya Summary Since the seventies, the establishment of hotels and other facilities has increased the pressure on the Kenyan coast. During the last decade, hotel managers and residents in Diani Beach have been experiencing problems with erosion. The only measures taken to address the problem are individually built seawalls to protect private properties. These seawalls are mostly not properly built and do not decrease the erosion rate. Erosion continues and beaches are still disappearing. In some places, coral rock is exposed or buildings collapse. The economy in Diani Beach is strongly depending on tourism. A white beach with a gentle slope and a flourishing ecosystem of lagoon and coral reef is desirable to attract tourists. The current situation in most parts of Diani Beach is far from desired. Diani Beach seems to be subject to structural erosion, due to several reasons. Initially, the narrowness of the African continental shelf leads to an easily loss of sediment into the deep ocean. Also the fact that there are no high mountain ranges along the Kenyan coast results in a low rate of sediment flowing into the ocean. A lack of sand combined with the relative stableness of the African crustal plate can be seen as causes for structural erosion. In Diani Beach the process is accelerated by a number of factors, both human and nature induced. Measures have to be taken to recover and maintain the desired situation. However, it is difficult to determine the optimal solution because of policy issues and lack of data. Several measures are proposed, which can be divided into three categories: management and policy measures, soft measures and hard measures. The first category implies e.g. determination of the setback line, altered approach to fishery and enforcement of legislations. Soft measures include planting of vegetation and beach nourishment. Breakwaters, groynes and improvement of seawalls are hard measures. A combination of measures can have effect on both short and long term, first recovering and subsequently maintaining the desired situation. However, more data have to be gathered to determine the best combination of measures, make a proper design and find the way to implement them. 5 Coastal Erosion Project Kenya Table of contents PREFACE......................................................................................................................................................... 3 SUMMARY....................................................................................................................................................... 5 TABLE OF CONTENTS ................................................................................................................................. 6 LIST OF FIGURES.......................................................................................................................................... 8 LIST OF TABLES.......................................................................................................................................... 10 1 INTRODUCTION................................................................................................................................... 11 2 PROBLEM DESCRIPTION .................................................................................................................. 14 2.1 PROBLEM ANALYSIS .............................................................................................................14 2.2 PROBLEM DEFINITION ..........................................................................................................14 2.3 MAIN OBJECTIVE ..................................................................................................................14 2.4 SUB OBJECTIVES ...................................................................................................................15 2.5 PROGRAM OF REQUIREMENTS ..............................................................................................15 3 THE PROBLEM AREA......................................................................................................................... 17 3.1 GENERAL ASPECTS OF KENYA ..............................................................................................17 3.2 GEOLOGY AND GEOMORPHOLOGY OF THE KENYAN COAST ..................................................19 3.3 DIANI AREA ..........................................................................................................................24 4 COASTAL ZONE MANAGEMENT IN DIANI BEACH................................................................... 26 4.1 PARTIES INVOLVED ..............................................................................................................26 4.2 REGULATION AND LEGISLATION ..........................................................................................27 4.3 FINANCING DEVELOPMENT IN THE COASTAL ZONE ...............................................................27 4.4 PROCESS OF DECISION MAKING ............................................................................................28 5 MORPHOLOGIC LITERATURE STUDY ON THE KENYAN COAST ........................................ 30 5.1 PHYSICAL CONDITIONS .........................................................................................................30 5.2 RIVERS .................................................................................................................................41 5.3 SEDIMENTOLOGY .................................................................................................................43 5.4 ECOLOGY .............................................................................................................................44