# Hydraulic Analysis of a Passive Wedge Wire Water Intake Screen for Ichthyofauna Protection
## 1 Introduction  
One of the most significant challenges of our time is to counteract the environmental degradation caused by man's intensive exploitation of natural resources. This impact is further compounded today by a climate that is changing before our eyes. Extreme weather events such as heat waves, heavy rainfall, and prolonged droughts are increasingly observed, which can lead to flooding, deterioration of water quality, and reduction of water resources as well as negatively affecting the existence of ichthyofauna [1; 2; 3; 4]. However, the biggest threat to the aquatic environment and ichthyofauna is the large intake of \"fresh\" water by humans. Due to human population growth, economic development, and changing consumption patterns a progressive increase in the amount of human water intake from the environment is forecasted in the coming years [5]. By 2050, it is estimated that there will be a 20-30 percent increase in the total amount of water used by humans worldwide,mainly for domestic and industrial purposes, including an 85 percent increase in water use for energy purposes [6; 7; 8; 9; 10; 11; 12]. Water intake is a key component of the water supply system in the context of guaranteeing the continuous intake of water in adequate quantity as well as quality. For water supply purposes, it is possible to use surface water, groundwater, and spring water. Groundwater intake can be carried out by means of wells and adits as well as drainage lines and galleries with different construction solutions. In the case of water intake from surface intakes, a distinction is made between shore intakes, bay intakes, stream (submerged) intakes, still intakes, and weir intakes [13]. Submerged intakes consist of three main elements: an inlet below the surface of the water table at an appropriate distance from the shore, a pipeline, and a collection chamber into which water flows by gravity or by a levitation pipeline. Among the traditionally used design solutions of submerged intakes, light type and heavy type are distinguished. Light-type intakes are most often made of steel pipe and seated at the bottom of the watercourse on supports made of reinforced concrete or steel piles, while heavy-type intakes require concrete or reinforced concrete casings. Among the light-type inlets, there are cup (conical), disc, or pipe ones [14]. They are characterized by a compact and simple design and the low cost of construction, but they can interfere with the flow of water in the watercourse and require the installation of fish protection devices. Heavy-type intakes are more expensive and more complicated to manufacture. The simplest design is the bucket pipe that protects the ends of gravity or siphon pipes. In this case, it is necessary to use devices to protect ichthyofauna and ensure that inlet velocities are not exceeding critical values. In the event of snow-ice conditions in the intake, heavy-type intakes with a vortex chamber are used. This type of intake is easy to flush and provides a uniform distribution of inlet velocities over its surface. A considerable disadvantage, however, is the difficulty of manufacture and availability. In difficult operating conditions (ice-snow phenomena, large amounts of trailing debris), filter intakes are used, which do not require the installation of devices to protect aquatic fauna, but they are complicated to install and usually require high pressures during flushing. Surface water intakes, which are generally characterized by higher yields than groundwater and spring water intakes, pose a major threat to ichthyofauna. Excessive velocities occurring in intake windows or screens can cause fish and fish in early stages such as fish fry and larvae that do not yet have sufficient swimming skills to be drawn into intakes, causing their death or severe injury [15]. According to the current regulations contained in the Habitats Directive [16] and the Water Framework Directive [17], there is an obligation for European Union member states to protect water resources, including ichthyofauna.