Scholarly record

RESILIENCE OF LARGE-SCALE WATER SUPPLY SYSTEMS TO CLIMATE CHANGE: A COMPARATIVE HYDRAULIC ASSESSMENT OF TWO DESIGN ALTERNATIVES FOR THE VACHA PROJECT

Boris Tzankov

Abstract

The “Vacha” Regional Water Supply System represents a large-scale hydraulic infrastructure project designed to ensure long-term, climate-resilient drinking water supply for the city of Plovdiv and 28 surrounding settlements, with a planning horizon to 2070. The system is based on regulated surface water abstraction from the Dospat–Vacha cascade and integrates hydrological, hydraulic, and energy analyses to optimize resource utilization under changing climatic conditions. The study draws upon primary technical, hydrological, and economic data obtained during the preparation of the Feasibility Study, led by the author as Chief Designer. The design discharge of the system reaches 222,298 m3/day (2,572.87 L/s) and is supported by a 150,000 m3 main storage reservoir for Plovdiv and a 12,000 m3 reservoir for the adjacent settlements. Two technically feasible hydraulic design alternatives are comparatively assessed. Both include a primary intake from the equalizing reservoir of HPP “Vacha 2” (elevation 327.50 m), a backup intake system implemented through a floating pumping station, a transmission pipeline partially integrated with existing irrigation tunnel infrastructure, a new water treatment plant, a 172–179 km regional transmission network, and five new pumping stations. The evaluation incorporates hydrological datasets (2009–2019), reservoir storage regimes, water quality monitoring (93 indicators), and compliance with national and EU water legislation. Although capital investments are comparable (approximately 340–386 million BGN), the alternatives differ in land-use impact and operational flexibility. The results demonstrate that both solutions significantly enhance regional water security by reducing dependence on climate-vulnerable groundwater sources and ensuring a regulated, high-quality surface water supply, positioning the project as a model for resilient water resource management. The research advances a methodology for the comparative assessment of climate-resilient regional water supply systems, combining hydraulic modelling, reservoir operation analysis, and infrastructure planning within a unified decision-making framework.

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