The management of transformed small river basins of Volyn Polissia – Buniv River case study

The assessment of the transformation level in the Buniv River basin (Ukraine) transformation was performed. Substantiates the need to improve the monitoring system within the river basin, as the main tool for assessing and predicting changes in the aquatic ecosystem and managing the processes of its anthropogenic. The research methods included on-site investigations, laboratory and analytical studies, data processing using GIS technologies. A topographic survey of the Buniv River’s floodplain within the village of Rokytne town was performed. The on-site investigations included field surveys and water sampling at 4 control sites on the Buniv River for 13 quality indicators. The analysis of the obtained cartographic models indicates a significant anthropogenic transformation of the natural landscapes. A significant part of the watercourses of the Buniv River basin was once directed and transformed into main canals of the meliorative systems. This causes the formation more dangerous flood flow.


Introduction
The current national environmental policy of Ukraine in the field of water management is aimed at the Implementation of the Water Framework Directive 2000/60/EC (EFWD) [1] on ensuring sustainable resource management, meaning the European Model of Water Resources Management.The EFWD aims to protect and improve the state of water resources and promote their sustainable and balanced usage.It sets out the basic provisions for EU countries to achieve good surface, ground, transitional and coastal waters within each river basin.In order to implement the EU's directives on river basin protection, the Verkhovna Rada of Ukraine preserved the integrated approach to water resources management based on the basin principle at the legislative level.For this, they adopted in 2016 under No. 1641 -VIII the Law of Ukraine "On the modification of some legislative acts concerning the introduction of integrated approaches in the water resources management by the basin principle"; on 26.10.2017under No. 25 the Order of the Ministry of Environment "On the allocation of sub-basins and water management areas within the established areas of river basins"; on September 19, 2018, under No. 758 the Resolution of the Cabinet of Ministers of Ukraine "On approval of the procedure for state water monitoring," etc.The above-mentioned law and bylaws are aimed at implementing a system of integrated water resources management based on the basin principle by: • Developing and adjusting the river basin management plans • Developing the water management balance sheet; • Determining the hydroecological state of the surface waters.
• Determining the powers of the central and local authorities, local self-government bodies in the implementation of water protection measures, etc.
In addition to this, the relevant State Agency for Water Resources of Ukraine is committed to developing the river basin management plans for 9 river basin districts.As of today, the water massifs and the typology of the general hydrographic network of Ukraine have been identified; the diagnostic and operational monitoring of the transformed surface water massifs has been carried out, and the reference conditions of the river basins have been established.Also, in 2021, plans were made to complete the works on creating classifications of the ecological state of water bodies, establishing their ecological and chemical states, as well as determining ecological purposes for these water bodies.
Volyn Polissia is transboundary region.At the same time, Ukraine has committed itself to implement the Convention on the Protection and Use of Transboundary Watercourses and International Lakes (Convention on Transboundary Waters) [2].The main purpose of this Convention is to approve the measures to protect and ensure the quantity, quality and sustainable usage of both surface and underground transboundary water resources at the local, national and cross-border levels.Within the Convention, the industry institutions should apply an integrated basin approach based on the understanding that water resources are an integral part of the ecosystem and play a crucial role in the socio-ecological and economic development of territories.
The Convention requires the states to fulfill certain obligations: to control and reduce the negative transboundary impacts on the hydroecosystems and river basin territories at the different levels; to apply an ecosystem approach in the field of common water resources management in compliance with the principles of "polluter pays", "cautiousness"; the conservation and the restoration of ecosystems; to implement environmental impact assessments; to set common goals to achieve a "good state" of water quality, monitoring the state of transboundary rivers; to minimize man-made risks, etc.
Therefore, today, in our opinion, it is extremely important to develop and implement a joint program for monitoring rivers and to apply a common tested and approved methodology for effective integrated water resource management of the transformed rivers.This includes the assessment of the ecological state of river basins using GIS technologies; determining the environmental goals to achieve a "good state" of water quality; developing compensatory water protection measures; developing the design and estimate documentation if necessary; the organizational tools for attracting water users, all interested parties, state authorities, and local self-government bodies, etc.Along with these important and topical issues is the need to ensure the flood safety of riverine territories of the Polissia zone, as well as adapting to climate changes.This is exactly the problem that arose in the basins of small rivers in the border areas of Volyn Polissia after the flood on May 17, 2018.Then, as a result of great precipitation, there was a rapid rise in water levels, which led to the flooding of residential buildings, including the threat of the destruction of the pressure front structures at the recreational reservoir in the Rokytne town (Rokytne), Rivne region [3].The heavy rain on May 16, 2018, which lasted about 10 hours, led to the flooding of 378 households located on the border territories of the Sarny district in the Rivne region, as well as the different infrastructure facilities.The most affected locations were those belonging to the basin of the Buniv River (a tributary of the Lva River).
Therefore, today it is important to use methodological approaches to protect, preserve and restore the surface waters of the Buniv River basin, which is the goal of our work.This research is devoted to developing the methodology elements for managing transformed basins of the small rivers at the border part of Volyn Polissia, substantiating technological solutions for the restoration and protection of the surface waters, which were tested on the example of the Buniv River basin.
In order to achieve the set goal, the following tasks were performed: on-site investigations and instrumental studies of the Buniv River basin were carried out; the ecological stability of the landscape and hydrological and morphological features of the river were assessed; the quality of the river's surface water and bottom deposits were assessed; management solutions were developed to achieve a "good state" of surface water quality according to the requirements of the EU WFD, as well as to protect the territory from floodwaters.
This report is a study on the changes in the ecological state of the Buniv River basin.The indicators that characterize the quality of river surface water and the compensatory organizational and technical solutions for restoring the aquatic ecosystem are the subject of the study.

Brief literature review
The Volyn Polissia waterways, especially the small rivers, are exposed to significant anthropogenic pressure [4][5][6][7].The quality of the surface water does not meet the requirements of the EU Water Framework Directive, and their current state is assessed as critical [8].In the border areas of Volyn Polissia, small rivers with their swampy catchment area and preserved forest vegetation form the water content, hydrochemical regime, hydroecological state and water quality of the basins of medium and large tributaries of the Prypiat.Unfortunately, the majority of rivers have been diverted, become shallow, and are affected by the pollution from diffuse and point wastewaters from industrial enterprises, agricultural production, utilities, etc.
A significant role in the destruction of the ecological situation in these river basins is played by non-compliance with the requirements of water legislation (Water Code of Ukraine) [9], deforestation, the "chemization" of agriculture, creating and functioning a cascade of ponds and reservoirs, violating the rules of operation in water bodies, violating the mechanisms of hydraulic structures (cross regulators) that do not provide water passage during floods and inundations, the intensive use of water resources, the discharge of significant volumes of polluted water, etc.Such a powerful transformation of the territories [6] and water areas of river basins at the border territories in terms of the scale of manifestations and the impact intensity makes it necessary to find ways to optimize resource management, develop compensatory water protection measures (technological road map) and integrate water resources management in these transformed river basins of the border territories [4,5].
Further delay in resolving this problem will lead to a decrease in the assimilation capacity of hydroecosystems of the Volyn Polissia river basins [10], and deterioration in the ecological situation of the main border artery, meaning the Pripyat River.For Ukraine and Belarus, resolving the above problems is extremely important, especially for the residents and water users living in the border areas that use surface water for various economic purposes.

Methods of factual analysis. Research area
The research methods included on-site investigations, laboratory and analytical studies, data processing using GIS technologies.A topographic survey of the Buniv River's floodplain within the village of Rokytne was performed.The on-site investigations included field surveys and water sampling at 4 control sites on the Buniv River for 13 quality indicators.A full-scale survey of individual sections of the river catchment area was carried out using an unmanned aerial vehicle.The chemical and analytical quality control of the Buniv River's surface waters was carried out according to regulatory requirements in the certified laboratory of water quality at the National University of Water and Environmental Engineering in Rivne city.The instrumental studies (dissolved oxygen content, oxygen saturation temperature, pH, ox-redox potential) were determined at the sampling site using certified mobile devices, the EZODO 7031 and Adva AD 11.
The procedure for sampling water at the Buniv River for hydrochemical analysis was carried out according to the relevant state standards: Water sampling for analysis was carried out under conditions for the river's lowest water content (during the summer low water period) at daylight hours.The sampling control points (research area located on N 51.280588, E 27.218915) assumed representativeness according to the level of anthropogenic load: 1-st section of the Buniv River, 50 m below the railway bridge (point PK-21); 2-nd section -Buniv River, 250 m below the railway bridge (point PK 18); 3-rd section -Buniv River, reservoir (PK10); 4-th section -Buniv River, the reservoir (PK3) (figure 1).The assessment of the Buniv River basin's surface water quality was carried out in accordance with the method of "Comprehensive Expert Assessment of River Basin Ecosystems" (IE) [11].
Sampling bottom deposits was carried out under the standards (DSTU ISO 5667-12-2001 Water quality.Sampling.Part 12. Guidelines for sampling bottom deposits [ISO 5667-12:1995, IDT]) on a 50 x 50-meter grid with a clamshell and capture area of 0.1 m 2 .Immediately after lifting the samples of bottom deposits, their field description was carried out.The mixed samples were used for further laboratory study and clarification with a lithological study of the bottom deposit composition.A total of 3 samples of bottom deposits in the Buniv River and 2 samples in the reservoirs were collected.For calculating the total pollution index we used the methods in force in Ukraine.

Description of the research area
The Buniv River basin is a typical small river of the border territory, located within the Sarny district of the Rivne region, a right tributary of the Lva river tributary (Pripyat river basin, 16-th ecoregion).The length of the river is 23 km, the slope of the river is 1.1 m/km.It is formed from many unnamed streams and reservoirs.The river has two main tributaries.An assessment of the Buniv River basin's territory was carried out based on remote sensing data (Sentinel 2, SRTM) and topographic maps (figure 2).As we can see, the catchment area obtained using DEM processing is not relevant to the actual real situation in south-western part (near villages Kysorychi and Masevychi).There, the network of drainage channels and regulation constructions has altered the conditions of flow accumulation.It's a good illustration of the necessity of using topographic maps for hydrological research within Volyn Polissia where similar constructions is widely spread.The analysis of the obtained cartographic models indicates a significant anthropogenic transformation of the natural landscapes.A significant part of the watercourses of the Buniv River basin was once directed and transformed into main canals of the meliorative systems (figure 3).As a result, the profile of the riverbed and its tortuosity have changed.The direction of the river's hydrographic network led to an increase in the slopes, carrying capacity, and speed of the flood wave.
Also, engineering surveys and a full-scale survey of the basin territory indicate that currently there is an increase in anthropogenic load on the river basin due to the overregulation of river flow, floodplain development, changes in morphological parameters, flooding of the territory, and so on.In our opinion, the changes in the structure and the water body's functioning parameters are a consequence of the manifestation of transformation and degradation processes that develop under the influence of natural and anthropogenic factors.
Today, the economic development of the catchment area is quite high.A significant percentage of the territory is located in residential areas; the floodplain of the river is disturbed and built In general, the Buniv River basin chosen for the study is typical for the border part of Volyn Polissia.Its main features include a significant transformation of the natural hydrographic network into a system of ameliorative channels by straightening riverbeds; the presence of waterregulating structures that are not always in good condition; the significant drainage of wetlands; the insufficient carrying capacity of some bridge crossings; the active use of floodplains for residential development and economic activities; the insufficient density of the monitoring system for registering extreme precipitation in the small river basins.
These factors pose a danger to aquatic ecosystems, the population and engineering infrastructure of the border areas.

Hydrological and morphological assessment of the river
For evaluating the valley and riverbed transformation, and undertaking management decisions on the flood safety of territory planning, we performed a topographic survey of the Buniv riverbed and valley within the most affected part of Rokytne.
The analysis of the constructed longitudinal profile along the river axis (the diagram is shown in figure 1) allowed dividing the study into five sections, differing in their carrying capacity and passing conditions of the flood wave.
1.The section near the railway bridge (from PK 24 to PK 19) has a length of 500 m.The average slope is 0.022%, rectilinear; it has ridge formations of bottom deposits with a length of 14..16 m. and a height of 0.3..0.4 m.This situation is typical for the Buniv River almost along its entire length.As a result, the first section has the appearance of the non-typical flat Polissia river (figure 2), and represents the principal channel.These transformations contribute to a shorter duration of water standing on the floodplain, but the floods become more pronounced with higher maximum costs.Thus, this section is estimated at a comparably high carrying and transport capacity, which intensely transfers water to the next section.2. The next section further downstream (from PK 19 to PK 16+75), with a length of 300 m, is characterized by a conditionally undisturbed current; it has a formed meander, as a result of which the channel slope decreases by 30%, having an average slope of 0.013%.A decrease in the river's slope leads to a decrease in the flow rate, the ability to carry deposits, and, accordingly, an increase in water levels at the maximum flow rates.3. Further, the riverbed (the section from PK16+75 to PK12.0 with a length of 475m) is under the influence of a bridge crossing.From the upper part, from PK16+75 to the bridge, the channel is positioned, due to the support of the stream by the river crossing.The water level on the site is close to the horizontal level and has a slope of 0.003%.A sharp drop in speed causes sediment deposits in this area during the decline of floods and inundations.In the future, shallow water will form on this site, additionally overgrown with higher aquatic vegetation.Further floods begin at higher bottom levels and, accordingly, at higher water levels.Below the bridge, there is an increase in the slope to 0.067%, a significant acceleration of the flow causing bottom erosion.This is due to the high rates of compressed flow coming out of the bridge opening.4. The next section (from PK16+75 to PK 6+75) with a length of 1000 m is the surface of the enterprise's reservoir and has a zero hydraulic slope.For a long time, the reservoir was not operated according to the design modes.Instead of the normal headwater level mark at 171.25, which is provided for in the project, the mark of 170.70 m is kept.This is due to developments at the territory previously allocated for the reservoir.Due to the decreased depth, the reservoir is a shallow water area with developed higher aquatic vegetation.From the point of view of flood safety, the section is characterized by low carrying capacity due to the significant overgrowth of the riverbed with aquatic vegetation and almost zero hydraulic slope.In addition, it determines the operation of the stage opening on the PK 13+30 in the flooded spillway mode, which approximately by 10..15% reduces its carrying capacity. 5.The section of the next reservoir also has a zero hydraulic slope.In addition to the functionality of the culverts, the reservoir is in a good condition.The lack of proper regulation of water discharge affected the scale of flooding in Rokytne during the flood on 17.05.2019,figure 4 shows the impact of existing engineering infrastructure on the formation of flood zones.As can be seen, there is an excessive compression of the river flow, which causes the flooding of the river valley.
We have calculated the maximum flow rate through the opening of the road bridge on 8 Bereznia Street in Rokytne.(indicated by the arrow in figure 5) for the flood conditions on May 17, 2019, as for a spillway with a wide threshold of 26.6 m 3 /s.This corresponds to a provision of 3%, that is, 1 time in 30 years; these floods can occur in the summer.

Proposed solutions Operation of culverts
The lack of water level regulation at culverts during the May 17-19, 2019 flood caused a shortterm overflow of water through the earthen dam.It has been established that the erosion of an earthen dam during the floods leads to a breakthrough and the formation of a wave with a great destructive force.This was prevented by the retention of a certain amount of water by the technical reservoir of the glass factory, as well as flooding of the floodplain above the automobile bridge.
In addition, the backup of water from this reservoir reduced the carrying capacity of the objects located upstream, which certainly contributed to a long stay of high water levels in the flooded areas.
Thus, a necessary condition for flood management is the development and implementation of a reservoir management plan depending on the meteorological situation in the river basin.

Technical capabilities of flood runoff redistribution
The technical capabilities for delaying this volume at the Buniv River's catchment area above Rokytne will allow floods in the banks of the river to pass through the village.However, the possible regulation of runoff should still include the release of water into the floodplain, as this is an important component of maintaining the ecosystem and the river water quality.
It should be noted that it is unlikely to find such opportunities without allocating land plots for polders or reservoirs.We estimated the flood volume to be 3.45 million m 3 .In order to retain this amount of water within the Buniv River's tributaries, it needs to have a total length of about 700 km.The river basin does not have such a developed hydrographic network.This approach also requires a significant number of regulatory structures at individual channels.
A technically possible method is to transfer part of the flood runoff (figure 5) from the Buniv River to the Lva River (above the villages of Masevychi, Buda) and the Berest River (in front of Rokytne and near Lisove village).
To do this, it is necessary to arrange either appropriate cross regulators, or lay pipeline structures that have a carrying capacity at a safe level for Rokytne's flow rates, whose value shall be determined by calculation.The economic feasibility of this type of construction should be justified by the agricultural, flood control and other needs and costs for their maintenance.
According to DSTU 7369:2013, the bottom deposits of the Buniv River belong to Group 1 of

Limnological surveys
The analysis results of the chemical element content in the bottom deposits of the studied section (table 1) indicate the presence of all six studied elements.

Hydrochemical assessment of the Buniv River's surface water quality
The surface water quality of the river was assessed using the main hydrochemical indicators, which are crucial in the formation of the surface water quality of Volyn Polissia's typical rivers.The summary results of the Buniv River surface water quality assessment, namely, the actual concentrations of biogenic substances, the multiplicity of exceeding environmental standards and the degree of surface water pollution are presented in table 2.
Ammonium and nitrogen ammonium.The concentration of ammonium in water bodies for domestic use should not exceed 2 mg N/dm 3 by nitrogen.MPC f ishf arm of ammonium salt is 0.5 mg N/dm 3 (by nitrogen) (this limiting indicator of harmfulness is toxicological).According to European standards, the concentration of ammonium in recreational reservoirs should not exceed 0.1 mg NH 4 /dm 3 .
The presence of ammonium ions is mainly associated with the processes of biochemical degradation of the protein substances, deamination of amino acids, and decomposition of urea under the urease action.The content of ammonium ions in natural waters varies from 12 to 205 mg N/dm 3 in terms of nitrogen.During the transition from oligotrophic to meso -and eutrophic reservoirs, both the absolute concentration of ammonium ions and their share in the total balance of bound nitrogen increase.
The presence of ammonium in concentrations near 1 mg/dm 3 reduces the ability of fish hemoglobin to bind oxygen.The signs of intoxication are disturbances, convulsions, the fish throws itself on the water and jumps to the surface.The mechanism of toxic action is a violation of the central nervous system, damaging the gill epithelium, hemolysis (rupture) of the red blood cells.The toxicity of ammonium increases with increasing pH medium.The increased concentration of ammonium ions can be used as an indicator that reflects the deterioration of the sanitary condition of a water body, the process of contamination of the surface and underground waters, primarily by domestic and agricultural effluents.
Nitrites and nitrite nitrogen.For nitrites, the MPC household is set at 3.3 mg/dm 3 as an ion of NO − 2 or 1 mg/dm 3 in terms of nitrogen.The MPC f ishf arm is 0.08 mg/dm 3 as an ion of N − 2 or 0.02 mg/dm 3 in terms of nitrogen.According to European standards, the concentration of nitrites in recreational reservoirs should not exceed 0.03 mgN − 2 /dm 3 .Nitrites are dissolved in surface waters.The acidic waters may contain small concentrations of nitric acid (HNO − 2 ) (not dissociated into ions).The increased content of nitrites in the Buniv River indicates an increase in the decomposition of organic substances under conditions of slower oxidation of NO − 2 into NO 3 −, which indicates the contamination of the water body.Nitrates and nitrate nitrogen.The MPC household for nitrates is 45 mg/dm 3 , or 10.0 mg/dm 3 (for nitrogen) and the MPC f ishf arm is 40 mg/dm 3 (by NO 3 −) or 9.1 mg/dm 3 (by nitrogen).According to European standards, the concentration of nitrates in recreational reservoirs should not exceed 5.0 mg NO − 2 /dm 3 .The presence of ammonium nitrate in concentrations of up to 2 mg/dm 3 does not cause a violation of biochemical processes in a reservoir; the maximum concentration of this substance, which does not affect the sanitary regime of the reservoir, is 10 mg/dm 3 .The harmful concentrations of nitrogen compounds (primarily ammonium) for various fish species are on the order of hundreds of milligrams per 1 dm 3 of water.
Phosphates.The MPC household for phosphates is 3.5 mg PO 4 2− /dm 3 , the MPC f ishf arm is 0.05 mg PO 4 2− /dm 3 .According to European standards, the concentration of phosphates in recreational reservoirs should not exceed 0.2 mg of PO 4 2− /dm 3 .The excessive phosphorus compounds from various sources such as mineral fertilizers, untreated domestic wastewater, and industrial waste are being carried by surface runoff from fields into the river.This inflow causes significant growth in the water body's plant biomass.As the concentration of phosphorus in the water increases, it changes the trophic status of the reservoir, leading to a restructuring of the entire water community.This restructuring results in the prevalence of putrefactive processes, leading to an increase in turbidity, salinity, and bacterial concentration.One of the components of the eutrophication process is the proliferation of cyanobacteria, also known as blue and green algae.Several of these algae produce toxins that fall under the category of phosphorus and sulfurcontaining organic compounds, which can be neuro-paralytic.The toxins produced by these algae can result in various health issues such as skin disorders and gastrointestinal ailments.In severe cases, paralysis may even occur when a substantial amount of algae enters the body.Biochemical oxygen consumption.The MPC household of BOD5 is 3.0 mg/dm 3 ; for MPC f ishf arm it is 2.0 mg/dm 3 .According to European standards, the BOD5 indicator is not normalized in recreational reservoirs.BOD5 identification in the surface waters is used to assess the content of biochemically oxidized organic substances, the living conditions of hydrobionts, and as an integral indicator of water pollution.
Dissolved oxygen.The MPC household for the content of oxygen dissolved in water is >4.0 mgO 2 /dm 3 ; for MPC f ishf arm it is >6.0 mgO 2 /dm 3 .According to European standards, the content of oxygen dissolved in water in recreational reservoirs is not normalized.The content of oxygen dissolved in water reflects the intensity of the processes in the hydrobiochemical systems.The oxygen identification in the surface waters is included in the observation programs to assess the living conditions of hydrobionts, including fish, as well as indirect features of surface water quality assessment and wastewater treatment management.The content of dissolved oxygen is necessary for aerobic respiration and is an indicator of biological activity (i.e.photosynthesis) in the reservoir.

Managing a transformed river basin
The assessment of the transformation level in the Buniv River basin makes it necessary to improve the monitoring system within the river basin, as the main tool for assessing and predicting changes in the aquatic ecosystem and managing the processes of its anthropogenic transformation.Water quality monitoring can be effectively supported through the use of satellite technology [12,13].
The basic model of monitoring the condition of the Buniv River and its objectives can be presented in the form of a diagram given in figure 6. Public environmental monitoring, if implemented, could be a valuable supplement to the existing system of monitoring water bodies.This will increase the availability of environmental information for all stakeholders, quickly obtain the necessary data in the event of an emergency accident, as well as current, regular monitoring of the impact of water users on the ecological state of the rivers.Local public organizations in the framework of public monitoring should perform the following functions: monitoring objects that are not included in state monitoring programs; implementing environmental control and notification of accidents and emergencies; developing environmental education and awareness; evaluating the environmental impact of projects for planned activities within river basins, etc.For the effective management of border area basins, including the Lva River, it is necessary to create a Basin Council, which will include the representatives of Sarny District Administration, the Rivne Regional Office of Water Resources, the State Environmental Inspectorate in Rivne region, scientists, public activists and water users of the river basin.The main task of Basin Councils will be to develop, coordinate and approve the River Basin Management Plans.An important issue in the Council's activities is monitoring the implementation of the planned water protection measures within the river basin.

Conclusions
For the effective management of water resources in border areas, it is necessary to develop and implement water protection measures that are defined in the river basin management plans and develop and implement a joint program for public monitoring of the cross-border rivers.
The increase in the social and economic risks in the study area and the material losses associated with flooding the households in the floodplain of the Buniv River are caused by anthropogenic factors, namely, the development of the river floodplain, the violation of the requirements of the Water Code of Ukraine and ignoring the danger from natural flood and overflow phenomena.
It is possible to reduce the threat of territorial flooding and ensure the flood safety of the river cross-border territories of the Polissia zone by applying organizational and economic measures and implementing the following compensatory hydraulic measures: • A periodic clearing of the riverbed section adjacent to the bridge from the deposits coming from the upper sections.This will help to increase the slope on the site, reduce the hydraulic resistance of the bottom turbulence and reduce the likelihood of spillway operation in semipressure and pressure modes; • Reducing the resistance of water flow at culverts and reservoirs, creating flood corridors.
Reservoirs require developing regulatory rules that provide for the level of water response depending on the current meteorological situation.Thus, if the amount of precipitation in three days reaches 20 mm, then it is already advisable to clear the river valley, prepare households for high water levels and work with both reservoirs in order to overcome flooding.
The most effective approach to prevent flooding of large areas of Rokytne is to prevent the inflow of significant water consumption within the city limits.To do this, one should: arrange structures above the village that will allow the transfer of runoff through a network of channels.
The surface water quality assessment shows that the overall ecological state of the surface waters of the studied aquatic ecosystem is assessed as unsatisfactory.The block of trophosaprobiological indicators is dominant and determines the water quality.At the same time, its deviation from the environmental standards is primarily caused by the biogenic elements of the nitrogen group (ammonium, nitrite and nitrate nitrogen) and phosphates.
In the upper and middle part of the river basin, it is necessary to carry out organizational and economic measures to reduce the inflow of pollutants with diffuse runoff, as well as hydraulic works to clear the riverbed and the riverbank stabilization.Also, in the middle section of the river, it is necessary to clean the surface waters of the river from the excess regional content, nitrite nitrogen, phosphates; we propose equipping a bioplateau according to the type of surface flow and an aeration treatment corridor.

Figure 1 .
Figure 1.The sampling control points location (marked in yellow) and diagram of the survey route (from PK0 to PK24).

Figure 2 .
Figure 2. Setting catchment boundaries according to satellite data (a) and topographic map (b).

Figure 3 .
Figure 3.Typical natural and directed sections of the Buniv River hydrographic network (image source: Google Earth Pro).

Figure 4 .
Figure 4. Fragment of the basin of Buniv River during the flooding on May 17, 2019 (model obtained using EOS Land Viewer).

Figure 5 .
Figure 5. Creating a possible redistribution of flood runoff.

Figure 6 .
Figure 6.Flowchart for surface water quality monitoring and management.

Table 1 .
Chemical composition of the bottom deposits of the Buniv reservoir.

Table 2 .
The Buniv River's surface water quality assessment.