Abstract
Addressing seasonal water uncertainties and increased power generation demand has sparked a global rise in large-scale hydropower projects. To this end, the Blue Nile impoundment behind the Grand Ethiopian Renaissance Dam (GERD) will encompass an areal extent of ~1763.3 km2 and hold ~67.37 Gt (km3) of water with maximum seasonal load changes of ~27.93 (41% of total)—~36.46 Gt (54% of total) during projected operational scenarios. Five different digital surface models (DSMs) are compared to spatially overlapping spaceborne altimeter products and hydrologic loads for the GERD are derived from the DSM with the least absolute elevation difference. The elastic responses to several filling and operational strategies for the GERD are modeled using a spherically symmetric, non-rotating, elastic, and isotropic (SNREI) Earth model. The maximum vertical and horizontal flexural responses from the full GERD impoundment are estimated to be 11.99 and 1.99 cm, regardless of the full impoundment period length. The vertical and horizontal displacements from the highest amplitude seasonal reservoir operational scenarios are 38–55% and 34–48% of the full deformation, respectively. The timing and rate of reservoir inflow and outflow affects the hydrologic load density on the Earth’s surface, and, as such, affects not only the total elastic response but also the distance that the deformation extends from the reservoir’s body. The magnitudes of the hydrologic-induced deformation are directly related to the size and timing of reservoir fluxes, and an increased knowledge of the extent and magnitude of this deformation provides meaningful information to stakeholders to better understand the effects from many different impoundment and operational strategies.
Highlights
The Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile is located in Ethiopia about 15 km upstream of the Sudanese border and is set to be complete in the several years [1,2]
A filling plan has not been finalized for the GERD, and, as such, we focused our input water load derivations and subsequent initial impoundment deformation modeling on representative filling scenarios as laid out in [5,7]. [5] utilized an 80-month filling strategy based on natural inflow rates from 1973–1978
The overall areal extent and volumetric water load for the full impoundment of the GERD (500 to 640 m) using the ALOS World 3D-30m (AW3D30) surface model and the methods outlined in Section 2.1 are ~1763.30 km2 and 67.37 Gt, respectively
Summary
The Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile is located in Ethiopia about 15 km upstream (east) of the Sudanese border and is set to be complete in the several years [1,2]. The initial GERD impoundment and subsequent reservoir creation along with seasonal fluxes in water levels due to operational phases cause large changes in both the areal extent and volumetric content of the reservoir. These marked variations in hydrologic loads can impart large forces on the surface of the Earth and are capable of deforming the lithosphere. The amplitude and extent of the flexural response is mostly dependent on the underlying rheology as well as the timing and amount of the hydrologic forcing Both the early filling stages and the subsequent operational scenarios play important roles in the application of hydrologic load induced lithospheric deformation for an impoundment of this size. In order to accomplish this task, we seek to answer the following questions: (1) What are the areal extents, reservoir volumes, and hydrologic loads from potential scenarios of long-term reservoir operation and multi-year reservoir filling schedules? (2) What are the modeled elastic flexural responses as caused by hydrologic loading variations from long-term reservoir operations and multi-year reservoir filling schedules at the GERD? We utilize digital surface models (DSMs) and hydrologic inputs from several filling and operational scenarios to answer (1), and we use those results along with a localized Earth model to compute the elastic displacements for each of the scenarios in order to answer (2)
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