Article Bathymetric Survey for Enhancing the Volumetric Capacity of Tagwai Dam in Nigeria via Leapfrogging Approach Pius Onoja Ibrahim 1,2 and Harald Sternberg 1, *   Citation: Ibrahim, P.O.; Sternberg, H. Bathymetric Survey for Enhancing the Volumetric Capacity of Tagwai Dam in Nigeria via Leapfrogging Approach. Geomatics 2021, 1, 246–257. https://doi.org/10.3390/geomatics 1020014 Academic Editors: Ana C. Teodor and Lia Duarte Received: 1 April 2021 Accepted: 28 April 2021 Published: 2 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Geodesy and Hydrography, HafenCity University Hamburg, 20457 Hamburg, Germany; pius.ibrahim@hcu-hamburg.de 2 Department of Surveying and Geoinformatics, Federal University of Technology Minna, PMB 65 Minna, Niger State, Nigeria * Correspondence: harald.sternberg@hcu-hamburg.de; Tel.: +49-40428275300 Abstract: From a global perspective, dams are constructed to trap water flowing from a higher concentration to a lower concentration into a basin for several purposes to aid humanity. The continuous monitoring of dams is prudent for measuring the rate of sedimentation and siltation, and to ensure that it functions to its full capacity. The Tagwai dam is used for irrigation and domestic activities. It was observed that there is a shortage in its storage capacity and supplies due to sedimentation, and coupled with this is the fact that the majority of the communities are not connected to the tap water system; if not, the problem would have been evidently pronounced. However, to determine the present volume of water and provide possible ways of increasing the reservoir’s storage capacity, the leapfrogging approach was used to improve the basin. The data were collected using a single beam echosounder and Hi-Target V30 differential global positioning system (DGPS). The sounder was used to acquire bathymetric data, while the DGPS was used to delineate the shoreline. The data were interpolated using the ordinary Kriging technique. After that, the leapfrogging method was grouped into four scenarios: Scenario A, B, C, and D. In each stage, the volume was computed using Simpson’s 3/8 integrated model. Scenario A is the present stage of the reservoir. Consequently, the results show that, while scenario B and C presented an appreciable increase in volume at the instant, scenario D illustrated a tremendous improvement in the storage capacity, and it is a win-win situation. The decision on which leapfrogging approach to employ depends on the government’s willingness to enhance the reservoir’s capacity and the resources available, such as human and financial capital to execute the project. Keywords: leapfrogging; scenario; bathymetric data; Kriging interpolation; volume enhancement 1. Introduction All over the world, dams are built to impound water for several purposes and to enhance developmental activities at different capacities [1–3]. Monitoring these dams is essential due to the negative effects of sedimentation and siltation on the storage capacity of any reservoir [4]. This menace, caused by sediment from the catchment area being trapped as a result of the constructed embarkment around the dam, “is most notably at the dam axis” [5,6]. Investigating the amount of deposited sediment or the reservoir capacity at any moment is only possible through a bathymetric survey, and a coinciding delineation of the shoreline, at the time of the survey [7,8]. The bulk of this material reduces the volumetric content, thereby causing a shortage of supplies [9]. Additionally, determining sedimentation distribution as it affects dam bed configuration and the number of deposited materials is achievable via bathymetric observation [2]. Bathymetric observation carried out using a single-beam echo sounder is deficient of footprints; therefore, the data acquired need inference in order to account for the sparse area [10]. If the interpolator components are selected well, the estimated output will be reliable, but will not fit as precisely as its counterpart obtained using a multibeam echosounder [11]. However, the estimated output Geomatics 2021, 1, 246–257. https://doi.org/10.3390/geomatics1020014 https://www.mdpi.com/journal/geomatics