Bathymetric survey of Lake Naivasha and its satellite Lake Oloiden in Kenya; using acoustic profiling system

Abstract

Lakes and reservoirs play important roles as freshwater sources for domestic, industrial, agricultural, fisheries and recreational purposes. However, for the lakes to be sustainably exploited, there is need to understand their bathymetric characteristics by conducting bathymetric surveys. This aids in generating information that can guide lakes stakeholders and managers in establishing the volume of available water. It is recommended, therefore, that bathymetric surveys be conducted at ten‐year intervals. Such continuous bathymetric information is lacking in many lakes, especially in developing countries. One example is Lake Naivasha in Kenya, which is largely exploited for various socio‐economic purposes. Despite its importance, its most recent published bathymetric data were collected in 1991. The goal of the present study, therefore, was to conduct a bathymetric survey of Lake Naivasha and its satellite Lake Oloiden, using an Acoustic Profiling System (APS) to generate Depth–Area–Volume relationships for the lakes. The survey results indicate the in the year 2016 mean depth, volume and surface area of the lake were 4.68 m, 722 × 106 m3 and 154.17 × 106 m2, respectively. Because of limited information from the 1991 survey, the 2016 survey results were comparable with those of 1983. The difference in the lakes mean, and maximum depth for the 1983 and 2016 survey was less by 0.23 and 2 m, respectively. This could be an indicator the lake is being affected by anthropogenic activities or environmental changes. The established Depth–Area–Volume relationships are crucial since they provide invaluable information to lake and water resources managers for making informed decisions regarding management of the lake's water resources.

The Storage and Water Quality Characteristics of Rungiri Quarry Reservoir in Kiambu, Kenya, as a Potential Source of Urban Water

“…A series of transect and tie lines was created as shape files in ArcGIS. The tie lines were oriented at 90 • to the transect lines, in order to improve data collection accuracy by cross-checking water depth measurements at their intersection with transect lines [9]. The tie lines provided independent measurements as well.…”

“…The trial run on the water was done to check the system response. The boats were then driven along the transect lines in the east-west direction and along the tie lines in the north-south orientation, prepared during pre-survey at a constant speed of 6 km/h to ensure safety and high quality data by preventing turbulence around the transducer [9]. Georeferenced depth measurements were obtained and recorded successively at each point using a 200 kHz signal.…”

“…Knowledge of available water in reservoirs guides stakeholders and managers in determining sustainable exploitation plan of the reservoirs [9]. Water body morphometry parameters provide information to assess residence time, life expectancy, water balance, sustainable water abstraction, and derivation of stage curves [10].…”

Sediment distribution and accumulation in Lake Naivasha, Kenya over the past 50 years

“…The findings of the present study imply that sediment focusing takes place in Lake Naivasha, wherein the deposited sediment is 1966-1996, 1996-2016 and 1966-2016 Site in Lake Naivasha F I G U R E 4 Lake Naivasha bathymetric and water depth contours map modified from Maina et al (2018) F I G U R E 5 Sediment thickness and distribution in Lake Naivasha over past 20-year period (1996-2016) resuspended and transported from shallower to deeper zones of the lake. As a result, the sediment deposition zones in the deeper parts of the lake are suitable for environmental archives (Shotbolt et al, 2005) that can be useful in establishing sediment accumulation rates.…”

“…The recent spatio‐temporal distribution of contaminants and their potential sources were established in that study. In another study on Lake Naivasha, the current bathymetric survey was conducted wherein water depth contours and the depth–area–volume relationship were generated (Maina, Sang, Mutua, & Raude, ). Thus, the objective of the present study was to assess the status of Lake Naivasha sedimentation, based on the distribution, thickness and volume of deposited sediment over the past 50 years.…”