Flooding of Lake Nakuru National Park and Its Effects on the Resident Wildlife

Lake Nakuru is one of Kenya’s Rift Valley Lakes and lies within the Lake Nakuru National Park. As a key habitat for flamingos and other water birds, the lake is a major tourist attraction. Lake Nakuru National Park covers an area of approximately 188 km 2 and is fully enclosed with a perimeter fence. The park is home to about 56 different species of mammals, 550 plant species, and 450 species of terrestrial birds as well as flamingos and other water birds. In the last decade, the lake has experienced continuous flooding, increasing the lake area from 35 km 2 in 2009 to 54 km 2 in 2018. This impacted negatively on the available space for wildlife. The main objective of this study was to investigate the effects of this flooding on the wildlife and their habitats in Lake Nakuru National Park. The methodology used Land use Land cover (LULC) interpretation of Landsat Satellite imagery from two epochs, 2009 and 2018, and integration of the results with relevant wildlife data provided by Kenya Wildlife Service. The results, which include LULC change maps and wildlife distribution maps, have shown that the flooding impacted negatively on the available space for wildlife. In addition, the floods also compromised key park infrastructures such as roads and the main gate making it very difficult to maintain the normal park operations, and hence adversely affecting the local and national economies. The information provided by this study is useful for planning mitigation measures in respect of the current and potential future flooding.


Background
Lake Nakuru National Park, covering about 188 km 2

Remote Sensing in Flood Change Detection
The flooding of Lake Nakuru National Park and the subsequent economic losses to the local and national economies represents a scenario that calls for mitigation measures, such as a rehabilitation plan and prevention of future flooding.
However, such decisions must be based on proper scientific data. Due to the large size of the area involved, the technologies of remote sensing and GIS can be used to efficiently acquire the said information, in terms of how the park has changed over the years of flooding. Such change detection involves the use of multi-temporal datasets to discriminate and quantify areas of land cover change between different epochs of imaging. Alternative approaches include image differencing and image ratioing involving the different epochs [5]. For this study, the first approach was taken. In addition to such mitigation measures (after the flood), remote sensing/GIS can also be used in the other two phases of a flood disaster management cycle, i.e. flood preparedness (before the floods) and flood response (during the floods) [6] [7].

Study Objectives
The key objective of the study was to investigate and document the effects of flooding on wildlife and their habitats in Lake Nakuru National Park; the documentation was to be largely vide land cover change, wildlife distribution and wildlife displaced habitat maps.

The Study Area
The study area consisted of Lake Nakuru National Park and environs, as shown in Figure 1.

Methodology
Data were extracted from the topographical map sheet, Landsat satellite images from 2009 (before flooding) and 2018 (after flooding), and wildlife census records. The data was processed in order to extract the required results of land cover change maps, wildlife distribution and a wildlife displaced habitats map.
This methodology is summarized in Figure 2.

Data Collection
Topographical map sheet number 119/3 at 1/50,000, which covers the Lake Na-

1) Topographical map
This was scanned and input to ArcGIS 10.6 software, where it was georeferenced. From the georeferenced map, basic park features were digitized. These features were to provide a topographical framework/background for subsequent thematic maps from the study.

Results and Discussion
1) Image classification for land use/land cover change Figure 3 shows the land cover classification maps for 2009 and 2018; the overall accuracies for these classifications were 73.5% and 75.0% respectively.
The subsequent land cover changes are shown in Table 1.  These results show a clear increase in the Lake category, and a corresponding decrease in the grassland and bare ground categories between the two epochs, which can be attributed to the flooding and growth of the Lake area. The sewage ponds for Nakuru town, which are at the northern edge of the lake, were clearly partly covered by the flooded lake. The reduction in bare ground and grassland represents a reduction in habitat for the animals that normally congregate in those categories.
2) Wildlife data analysis Table 2 shows the statistics for the wildlife numbers in the 13 blocks, while Table 3 shows the breakdown of the animal numbers to individual species.    From Table 2 and Table 3

Conclusion
This paper has documented a study that has quantified the extent of flooding in the Lake Nakuru National Park, and the effects of the flooding on wildlife habitats in the park. The wildlife habitats affected included bare ground, grassland and forest. This led to a reduction of wildlife dispersal areas and especially limited their territories near the lake, which in turn led to the migration of some species, such as rhinos, giraffes and elands from their original habitats to new unflooded habitats. The floods also adversely affected some park infrastructure such as roads and the main gate rendering normal park operations difficult. The results of this study have demonstrated the ability of remote sensing and GIS for this kind of study and can be used to inform decisions on park rehabilitation and future floods prevention and mitigation.