ISSN 0097-8078, Water Resources, 2018, Vol. 45, Suppl. 1, pp. S39–S49. © Pleiades Publishing, Ltd., 2018. Justification of Hydrological Safety Conditions in Residential Areas Using Numerical Modelling V. V. Belikova, *, A. I. Aleksyuka, b, N. M. Borisovaa, E. S. Vasilievaa, S. V. Norina, and A. B. Rumyantseva aWater Problems Institute, Russian Academy of Sciences, Moscow, 119333 Russia bFaculty of Mechanics and Mathematics, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received June 14, 2018 Abstract—The present paper looks at the application of modern technology of numerical modelling to simu- late natural and human-induced river floods of residential areas. The modelling is based on the use of 2D shallow-water equations and 3D digital terrain models. The application of adaptive mesh generator and effec- tive algorithms of parallel computing using NVIDIA graphics processors with CUDA technology enables cal- culating the areas and depths of flooding in a big city, taking into account all residential, industrial, and road constructions. Each one of them is specifically singled out on the mesh. This enables the reproduction of the real course of a flood well. Keywords: residential areas, flood, dam-break wave, flooded area, numerical modelling DOI: 10.1134/S0097807818050305 INTRODUCTION According to the existing standards, settlements along rivers must be protected against flash-floods, People have settled along rivers from time imme- wind set-up, and groundwaters with filling or morial. Nowadays, due to the growth of big cities, the embanking. The edge of the reclaimed territory should increase in the number of summer houses and cot- be no less than 0.5 m above the predicted high-water tages, as well as the development of road infrastruc- level with regard to the wave height at wind set-up. ture, the human impact on floodplains and river banks The extent to which the crest of a flood-breaking dam is becoming stronger. The authors of the present paper exceeds the predicted level should be set depending on have recently been involved in hydrodynamic model- the class of structures pursuant to sets of rules ling of floods in order to ensure the hydrological safety Nos. 104.13330.2016 and 58.13330.2012 [8, 10]. of several large objects. These include Oktyabrsky According to set of rules No. 42.13330.2011 [9], the island in the Pregolya River (the City of Kaliningrad), predicted high-water level should be set at the highest where a football stadium with the appropriate infra- water level recurrent every 100 years for urban (or to- structure was built for the 2018 FIFA World Cup; the be built-up) areas with residential and public build- left-bank floodplain of the lower Don (the City of ings, and every 10 years for parks and ‘plane’ sports Rostov-on-Don)—an area under active development venues [9]. It is forbidden to construct any buildings, where a football stadium for the 2018 FIFA World Cup facilities, utilities, or transport infrastructure in the was constructed; part of Kuznetsovsky boat-yard of flood-prone areas (with the flooding depth equal to or the Belaya River floodplain, which will be trans- exceeding 1.5 m) that are not supplied with flood-pre- formed into a new district of the City of Ufa; vention engineering systems [9]. Zakharovskaya floodplain of the Moskva River, where Residential areas situated in river floodplains con- cottages will be built; ‘Kamskaya valley’—the pro- siderably influence the water level and flooding areas spective development area in the floodplain of the of natural or industry-induced river floods. This cre- Kama River (the City of Perm); the City of Yaroslavl ates additional hydraulic resistance due to the flows on the Volga River; etc. Almost all these objects, apart around obstacles. Of vital importance here is the fact from being threatened by natural floods, can also be that the resistance that has to be considered in calcu- influenced by waves breaking through the hydropower lations is form drag, not friction. It cannot be structures upstream (not based on a real danger). This described in simple relationships like the Manning complicates calculating flood areas and their depth, formula. Dense residential areas and road dams across and leads to stricter safety requirements in the pro- floodplains affect the water level and flood zones most spective construction areas. significantly. If areas are protected by dams or filling, S39 S40 BELIKOV et al. it is necessary to calculate the maximum flooding lev- After it was constructed, the maximum flood dis- els taking into account the fact that the flow is con- charge in the lower pool, as well as the levels of a flood stricted by these objects. In some cases, due to histor- of 1%-probability, have dropped considerably. How- ically formed housing development, localities are not ever, there is now a hypothetical danger that a dam- protected against floods with any engineering systems. break wave may emerge at the waterfront of the hydro- This can lead to natural disasters like the flooding of power construction. Considering the dense residential Krymsk in 2012 [1, 6]. That is why it is necessary to areas of the city, it is needed to single out the areas predict the maximum parameters of flooding and its where construction is possible without security mea- dynamics in order to devise an evacuation plan and to sures and the areas where such measures are necessary, alert the population. and to what extent. The available data on the existing gauging stations In order to simulate dam-break waves and to deter- (the number of which in Russia has been sufficiently mine the hydrograph of outburst spates, a numerical reduced recently) does not allow the tasks in hand to model was designed representing a part of the Volga be fully completed due to the following. River valley from the upper reach of Rybinsk Reservoir (1). The instrumental monitoring period may not down to the mouth of the Kuban’ River (downstream witness extreme spates of low probability (1% or less). of Kostroma). The river reach is over 300 km long (2) Even if such floods occurred long ago, due to (Fig. 1b) and includes Rybinsk HPP, residential and the human-induced impact on the floodplain (e.g., industrial areas, as well as Yaroslavl road infrastruc- the construction of reservoirs and roads, bottom deep- ture. The model includes both the upper pool ening of river channels, etc.), the real correlation (Rybinsk Reservoir) and the lower pool (Gorky Reser- between water levels and discharge may considerably voir), which helps to accurately calculate the discharge change (which is often the case in practice). through a dam (because of a dam-break) taking into consideration the influence of the lower pool. It is also (3) In selecting high-altitude solutions for new necessary in order to realistically reproduce the development sites that comprise vast floodplain areas, dynamics of a dam-break wave. one needs to take into account the way they may affect the hydrological regime, which is difficult to do based The calculations were carried out based on 2D only on earlier observations. shallow-water equations according to a unique numer- ical algorithm [2] integrated in STREAM 2D CUDA (4) Observations at gauging stations alone are not software [3]. enough to predict the parameters of waves breaking through the hydropower constructions upstream (not based on a real danger). In such a case it is necessary Digital Terrain Model to calculate engineering constructions protecting resi- The first step in building up the computer model dential areas. was to produce a digital elevation map. The electronic Taking the above mentioned into account one can topographic map at a scale of 1 : 200000 was combined see the necessity to apply numerical simulation to with vectored pilot charts of the Volga River valley and complete the tasks in hand. A model must adequately with the electronic isohypses, both vectored based on reflect all the peculiarities of flood flows with respect maps at a scale of 1 : 25000. The topography of Yaro- to buildings, safety constructions, bridges, and the rest slavl was determined by vectored topographic maps at of the infrastructure in the floodplain; it must take a scale of 1 : 500 and at a scale of 1 : 2000. Rybinsk into account the nonstationary character of the flow, HPP was digitized based on its plans. Afterwards, a 3D as well as the deformation of the river channel (if digital terrain model (DTM) was formed composed of needed), etc. The model should be calibrated against nodes and isohypses in Cartesian coordinates X, Y, Z factual data, which, among other things, presupposes (Fig. 1b). retrospective analysis when applied. The present paper The input data for the DTM of Yaroslavl was its illustrates a modern technology and methodology that large-scale topographic maps provided by the admin- can be applied to a numerical simulation of flooding of istration of the city. The maps showed the computa- residential areas, as shown on a particular example. tional domains at a scale of 1 : 500 and at a scale of 1 : 5000 (in electronic vectored format). THE OBJECT OF RESEARCH The following data was additionally used. AND NUMERICAL HYDRODYNAMIC MODEL —The DTM along the course of the Volga River The City of Yaroslavl, whose population amounts from the site of Rybinsk HPP to the mouth of the to 700 thousand, stretches along the banks of the Kuban’ River at a scale of 1 : 25000 and 1 : 200000 (the Volga River (part of Gorky Reservoir) over 30 km floodplain) and 1 : 25000 (the river channel). (Fig. 1a). Rybinsk Hydroelectricpower Plant (HPP) is —The refined GIS of the morphometry of Gorky situated 100 km upstream.