ENVIRONMENTAL REVITALIZATION OF THE RIVER BASINS OF THE GUAPIAÇU AND MACACU RIVERS TO INCREASE WATER SECURITY IN THE EASTERN REGION OF GUANABARA

Purpose: Evaluate the implementation of interventions with environmental sustainability in the Guapiaçu and Macacu river basins, in Rio de Janeiro, based on the concept of nature-based solutions, for the regulation of river flows. Theoretical reference: Principles that assess the water retention of rainwater through infiltration in slopes and plains of valley bottoms in the basin, in order to mitigate volumes of surface runoff, and increase artificial recharge of the aquifer. Method : The methodology presents data on the characterization of the Guapiaçu and Macacu basins, as well as information regarding the collection of hydrological data, specifically related to streamflow measurement in both basins. Results and conclusion: The results indicate periods of flow rates above average, corresponding to annual river discharges, with flood flows reaching over 120 m3/s in the Guapiaçu River and 220 m3/s in the Macacu River, with high availability of rainfall runoff in the region. Research implications: Proposed interventions for environmental sustainability in the Guapiaçu and Macacu river basins, with a forecast of increasing the minimum flow rates of the Guapiaçu and Macacu rivers to meet the expansion of water supply for the Baía de Guanabara region. Originality/value: The proposal for revitalizing basins through unconventional and nature-based solutions has less impact and presents originality, as it ensures the sustainability of water resources with water security in water supply associated with lower cost.


INTRODUCTION
Water security in the water supply is fundamental to the development of any region.Depending on the need by the Government of the State of Rio de Janeiro to expand the supply of water to the Region of the Fluminense Contheast, the alternative of the construction of the Guapiaçu River Dam was originally studied due to the recurrent problems in the uptake of the Immunana-Laranjal system, which in the very dry periods does not work at full load due to lack of water in the Canal do Imunana (ENVIRONMENTAL ENGINEERING AND CONSULTING, 2013).However, the solution of the dam construction tends to generate negative environmental impacts, without efficient mitigating measures.An analysis of the negative environmental impact of the Guapiaçu dam has highlighted aspects related to the Environmental Impact Assessment (EIA), which addresses the possibility of the blossoming of potentially toxic algae, with the creation of the artificial reservoir generated by the construction of the Guapiaçu river dam.That is, the dam tends to generate an increase in stagnation of the waters of its generated reservoir, with production, as a consequence, of the process of water eutrofication, with the flowering of algae, and a worsening of the quality of the waters of the reservoir, including with the formation of cyanotoxins (ÁLVAREZ et al., 2017;CETESB, 2013;HOWARD et al., 2021;MATLOCK et al., 2013).
The dam also causes the obstruction of sediment transport in the river, with a profound change in the morpho-sedimentological equilibrium of the river water ecosystem, and the possibility of occupying the dead volume and the useful volume of the reservoir by silting up the sediments retained by the dam, at the same time that there will be a greater erosive tendency of the trough downstream of the dam (LI et al., 2021;LIU et al., 2022).
Fertile soil flooded in much of the reservoir area of the dam in the Guapiaçu River, regardless of the carrying out of deforestation and the cleaning of the reservoir area (foreseen in the original EIA), should promote the contamination of the waters of the artificial reservoir (LI et al., 2021;LIU et al., 2022;NEBEL;WRIGHT, 2000).
The generation of unemployment and the local socioeconomic problems can also have impacts due to the implantation of the reservoir, besides economic damage to the State of Rio de Janeiro (by the loss of agricultural productivity due to the flooding of these fertile and productive areas in food for the population of the State).
Another high-magnitude environmental impact, with potential for degradation of the natural water ecosystem from the construction of the Guapiaçu River dam, is the deterioration in the river's biodiversity (LI et al., 2021;LIU et al., 2022;NEBEL;WRIGHT, 2000).The Guapiaçu River, which currently has running waters and its natural biodiversity still preserved, will suddenly have stagnant waters in the whole region of influence of the backwater of the artificial reservoir formed, whose flood area is expected to be around 2,000 hectares (ENVIRONMENTAL ENGINEERING AND CONSULTING, 2013), which, besides suffering from water eutrofication (with the deterioration of the quality of its waters, including for human supply), will have their fauna and flora negatively impacted.It is important to point out that the biodiversity of a water body is highly influenced by the current velocity of this water body (LI et al., 2021;LIU et al., 2022;NEBEL;WRIGHT, 2000); when this natural current velocity of the Guapiaçu river is interrupted by the construction of the dam, with the formation of the artificial reservoir, its waters will stagnate, and a large part of the biodiversity of the river will be impacted, with ecological damage to fauna and flora.
On the other hand, sustainable and less costly water security solutions exist, including reforestation and increased permeability of the basin's soil (ANAND; KARUNANIDHI; SUBRAMANI, 2021;CRISTINA et al., 2011;DUONG;DE GROOT, 2020;GROLLEAU;MCCANN, 2012;HANLON, 2017;NEBEL;WRIGHT, 2000;OTTONI, 119 96;OUYANG;LEININGER;MORAN, 2013;RANI et al., 2022;STORY;FORSYTH, 2008;ZEMA et al., 2021), which also ensures an increase in the volume of water available to the water supply system for the population and the preservation of the river ecosystem, without impacts on local farmers and the entire population of Rio.
The present study aims to evaluate the implementation of interventions with environmental sustainability in the watersheds of the Guapiaçu and Macacu rivers, starting from the concept of nature-based solutions, for the regularization of river flows, reduction of floods in the rainy periods and maximization of the flows of these rivers in the periods of prolonged droughts.The interventions proposed in this article are based on the increase of infiltration of rainwater in the soil, in the recharge of flows, and on the increase of reforestation areas, above all in Permanent Preservation Areas (PPAs), as marginal bands of the rivers and in steep areas of the river basin for the recharge of water sources.

The Technological Solution for Regularizing River Flows in the Guapiaçu and Macacu River Basins, as a Guarantee of Water Supply in the Region
The proposal to regularize the flow forecasts the reduction of volumes of floods during periods of intense rainfall with an increase in the water availability in the river basin of these rivers during periods of drought, and of water flows in the Canal de Imunana (which receives the exudates of the Guapiaçu and Macacu rivers), of up to more than 5 m3/s, used by the concessionaire to supply the population in the region of the Fluminense Contheast.With the revitalization project, there will be no need for new river abstractions, nor for the transposition of flows from other river basins.
The objective of the interventions is to promote water retention of rainwater and the reinforcement of infiltrations in the slopes with slopes of different slopes and valley plains of the basin, with minimization of surface runoff, through artificial recharge actions, the use of small and medium hydraulic works and reforestation strategically distributed along specific areas of the river basin, depending on their anthropic occupation process (CRISTINA et al., 2011;GROLLEAU;MCCANN, 2012;HANLON, 2017;USAVIJAD et al., 2022;MURATOGLU;IRAZ;ERCIN, 2022;OTTONI, 1996;OTTONI et al., 2019;OTTONI;SAMPAIO;VASCONCELOS, 2017;STORY;FORSYTH, 2008).This results in a reinforcement of the water in the groundwater and the consequent hydrosedimentological regularization of the draining river gutters of the basin, as well as the retention of surface water from the slopes that would move rapidly during periods of heavy rainfall to the galleries of rainwater and river gutters, and an expansion of the magnitude of urban flooding, both in the basin of the Macacu River and in the Guapiaçu River.Therefore, favorable effects are promoted for the mitigation of floods (in the periods of intense rainfall in the region), with benefits to the natural ecosystem of the river basin, control of erosion and silting, besides an improvement in the conditions of humidity of the soil.In this way, better support conditions are provided for the fixation of floristic coverings and the consequent enhancement of ecological biodiversity and natural environmental conditions; Reforestation is the ideal way of controlling surface water runoff.In forested areas, the soil surface layer, consisting of humus and root zone, normally has a high capacity for absorbing rainwater and consequently reducing surface runoff, while the flower cover region acts as a real obstacle to surface runoff passage, so as to favor water infiltration processes and reduction of soil erosion processes(GROLLEAU; MCCANN, 2012;HAJDUKIEWICZ;WYŻGA, 2022;HANLON, 2017;MOUSAVIJAD et al ., 2022;NEBEL;WRIGHT, 2000;OTTONI, 1996;OUYANG;LEININGER;MORAN, 2013;STORY;FORSYTH, 2008;WU;CUI;HUANG, 2021;XIANG et al., 2023;ZEMA et al., 2021;ZHU et al., 2020).The heterogeneous flora coating has a great importance in the ecosystem of the river basin, since it generates an improvement in the climate and air quality of the region; it increases the natural process of fertilizing the soil (formation of the humus); it retains more water in the soil, reinforcing the humidity of the land (increase in plant productivity) and recharges the groundwater; it increases the environmental humidity of the ecosystem, as one of the fundamental elements for the elevation of the ecological biodiversity of the river basins and the health and well-being of the human beings who inhabit them.The consequence of all this process of environmental preservation of the river basins is the significant increase in minimum river flows during periods of drought, with more water security for the supply of human water and environmental sustainability in the water management of natural waters (DEL CAMPO et al., 2019;GROLLEAU;MCCANN, 2012;MURATOGLU;IRAZ;ERCIN, 2022;OTTONI, 1996;OTTONI et al., 2019 VAN DER VALK, 2019;SILVA, 2015;SOUZA, 1979;STORY;FORSYTH, 2008).It is important to highlight the favorable influence of the forest in the control of the surface runoff of the slope, where it is found that the surface runoff coefficient for a forest soil is 0.15 to 0.20 (MIGUEZ;VEROL;REZENDE, 2016;OTTONI, 2022aOTTONI, , 2022b;;SILVA, 2015) (that is, 15 to 20% only of the rainwater that precipitates over the basin is that drains superficially; around 80% of these waters are drifted into the soil, with damping of flood peaks and guaranteeing river continuity, even during prolonged periods of drought, by increasing the basic flow of the groundwater).In a bare and compacted soil, the runoff coefficient can reach 0.70 or more (i.e., the opposite situation, where 70% or more of the rainwater is transformed into surface runoff from the hillside and rapidly flows towards the rivers, with the impact of flooding; and during periods of drought, the rivers become drier due to the low water recharge to the groundwater sheets during periods of rainfall) (MIGUEZ; VEROL; REZENDE, 2016; SILVA, 2015; SOUZA, 11 979).
In addition to reforestation, it is proposed that slopes should be built to recharge aquifers in the short term.These civil works, usually of small size and low cost, can be: the slope sills (in the steepest parts of the basins, with the aim of dissipating drainage energy and retaining sediment from the soil), the terracing or infiltration ditches (in the areas of intermediate slope of the slopes, aiming to retain surface runoff and infiltrate them into the soil), the recharge basins (in the flatter and lower areas, where infiltration plains are formed, widely recharging the groundwater in the rainy periods), and interventions to control soil erosion (CRISTINA et ., 2011;DEL CAMPO et al., 2019;OTTONI, 1996;OTTONI et al., 2019; OTTONI; OTTONI, 2022; OTTONI; SAMPAIO; VASCONCELOS, 2017; SALAMEH; ABDALLAT; VALK, 2019; SALAMEH; ABDALLAT; VAN 9;ZHU et al., 2020).
These actions and engineering works, such as structural measures, are dimensioned with the objetive of meeting the recharge values provided for in the projects for the spatial regularization of flows, and promotes a greater uniformity in the hydrograms of the rivers.The slope sills are small dikes formed by blocks of dry mortar stones or gabions, arranged in heights ranging from 0.5 m to 1.0 m; the gabions are arranged according to the alignment of the level curves of the river basin, with spacing from several meters to a few tens of meters and extension of tens or hundreds of meters.These works should usually be located in steeper stretches of the slopes, and implanted in higher stretches of the dynamic zone and along the moisture reinforcement zone of the watershed, because they have the function of retaining eroded solid material and dissipating the energy of the surface runoff of the slope water; over time, with the silting of the slope threshold, it is possible to enlarge its height through new threshold in steps, with greater horizontality of the land (less energy of surface runoff of the slope) and a consequent recovery and improvement of the quality of the soils (OTTONI, 1996;OTTTTTONI;ONI et al., 2019;OTTONI;SAMPAIO;VASCONCELOS, 2017).In this way, the silting and pollution of the waterways and lakes by the carrying of the solid material of the hillside is avoided.The main purpose of the infiltration and terracing trenches is to recharge the groundwater from the retention of the surface runoff of the slope and infiltration into smallslope trenches, which are also aligned according to the direction of the level curves.These structures are constructed on less sloping stretches of the slopes, normally in lower stretches of the moisture reinforcement zone and in the dynamic zone of the river basin, and a floral coating should be fixed to the downstream face of these structures; spacing between them is a function of the slope slope, the nature of the soil and the estimated volume of the water defluviums to be contained (ANAND; KARUNANIDHI; SUBRAMANI, 2021;OTTONI, 1996;OTTONI et al., 2019 In the lower and flatter regions of the river basin, close to the river gutters, it is common to implant the recharge basins, which have the function of retaining and infiltrating the surface waters of slopes that can still reach there, coming from the rains.They are usually located in the lower part of the dynamic zone and in the initial contribution zone, characterized by small lateral dikes of containment, or else excavated in the soil, and implanted in porous terrain, and it is also convenient to plant grasses in its periphery near the river gutters (ANAND; KARUNANIDHI; SUBRAMANI, 2021;OTTONI, 1996;OTTONI et al., 2019; OTTONI; OTTONI, 2022; OTTONI; VASCONCELOS, 2017; SALAMEH; ABDALLAT; VALK, 2019; SALAMEH; ABDALLAT; VAN DER VALK, 2019;STORY;FORSYTH, 2008).
Figure 1 shows schematically the works and actions of slopes indicated for spatial regularization of river flows aiming at drought and flooding mitigation in river basins, which are more indicated for rural areas.These actions to control the flow of the slopes tend to regularize the flow regime in the basin, to reduce the peaks of the flood, to reinforce the flow of the drought (flattening of the hydrograms), shown in Figure 2 VAN DER VALK, 2019;SILVA, 2015;SOUZA, 1979;STORY;FORSYTH, 2008), as well as reducing the transport of solid materials and progressively improving water quality.All these results contribute to the ecological and environmental enhancement of the ecosystem of the river basin, which is subject to various human activities (sustainable development).These types of actions reinforce the minimum flows of the Guapiaçu and Macacu rivers during periods of drought, in order to provide a guarantee of water supply for the population of the eastern region of Guanabara Bay, and generate positive environmental impacts to the ecosystem of the river basin of these rivers.Figure 2 shows that the increase in artificial flow recharge in a river basin tends to lead to an appreciable reduction in flooding, since a good part of the rainfall waters over the river basin (during the rainy months, within the hydrological cycle) will be retained in the soil and infiltrate the reservoir of nature, which are the groundwater and the artesian ones.The magnitude of this water retention in the basin will vary as artificial recharge interventions on the slopes are extended (BACHA et al., 2022;OTTONI, 1996;OTTONI et al., 2019;OTTONI;SAMPAIO;VASCONCELOS, 2017).Likewise, during the months of the dry period within the hydrological cycle, river flows are reinforced with the minimum river flow doubled or more (ANAND; KARUNANIDHI; SUBRAMANI, 2021; OTTONI, 1996; OTTONI; OTTONI, 2022; SALAMEH; ABDALLAT; VAN DER VALK, 2019;SOUZA, 1979).
The entire upper hatched area shown in Figure 4, of runoff in the rainy periods, would infiltrate with increase of the base flow to the river ΔDB1 and ΔDB2 (reduction of its flows of floods, whose water would be retained strategically in the soil of the river basin), due to the greater recharge of the groundwater, and in the periods of drought, the base runoff (of the underground water feeding the rivers) would be greater, with increase of the minimum flow, for the purpose of reinforcing water supply for the population.The pasture areas correspond to approximately 40% of the total area of the Guapiaçu and Macacu river basins.The runoff of these grassland regions is higher than 0.5 -0.6 (MIGUEZ; VEROL; REZENDE, 2016; SILVA, 2015; TUCCI; PORTO; DE BARROS, 1995) (that is, at least 50 to 60% of the precipitated waters in these grassland areas drain away superficially, aggravating flooding in rainy periods, and this water is lost towards Guanabara Bay, without retention in the river basin where the rivers are located).This occurs mainly where soil erosion occurs in several of these grassland areas (where many of them are degraded), so it is intended to act in the protection of the soil in these places, to increase the recharge of the groundwater in these regions.

METHODOLOGY
Based on the technical analysis of the environmental impacts generated by the possible implementation of the Guapiaçu river dam (ENVIRONMENTAL ENGINEERING AND CONSULTING, 2013), a study was prepared for the implementation of a sustainable technological alternative, within the concept of nature-based solutions, through the spatial regularization of river flows, as a guarantee in meeting the water demand for the supply of the population of the Guapiaçu and Macacu river basins.According to Ottoni (2019), the Guapiaçu and Macacu river basin system has an area of 570.34 and 507.69 km2, respectively.They are basins responsible for the production of various types of vegetables for the State of Rio de Janeiro, with rivers that serve the main water sources 10 of the eastern region of Guanabara Bay, in the State of Rio de Janeiro.This system currently operates at its limit, with a flow of 6.0 m³/s, and in the future, for a scenario referring to the year 2035, there will be a water deficit of 5.0 m³/s (ENVIRONMENTAL AND CONSULTING, 2013).The Guapiaçu and Macacu basins show high agricultural productivity for the State of Rio de Janeiro with the production of more than 20 thousand tons a year of products, such as: green corn, yams, aypim, guava, jiló, silver banana, okra, tahiti lemon, green coconut, and others (Figure 5) (adapted CRISTINA et al., 2011).The Guapiaçu river basin features areas of deforestation, erosion and soil compaction, with increased volume of surface slope runoff, impacts on the reduction of water infiltration in the soil and the consequent silting of the Guapiaçu river (ENVIRONMENTAL ENGINEERING AND CONSULTING, 2013).

Characterization of the Guapiaçu and Macacu river basins
As a result of the disorderly and poorly planned development of human populations in the Guapiaçu and Macacu river basins, these actions basically lead to greater soil sealing from the increase in surface water runoff values (COELHO, OHNNUMA JR, FONSECA, 2023; MIGUEZ; VEROL; REZENDE, 2016; NEBEL; WRIGHT, 2000;OTTONI, 1996;SILVA, 2015;Y;FORSYTH, 2008;ZEMA et al., 2021).The consequences of these environmental impacts are reflected, for example, in widespread erosion and silting in the basin; soil humus loading and associated depletion; increase in flood peak due to increased surface runoff from reduced infiltration rates; surface water pollution due to the loading of slope materials, including residues from human activities, brought by surface runoff; decrease in ecological biodiversity of the natural ecosystem; and widespread health problems (CUNHA et al., 2022;LÓPEZ, 2022 MURATOGLU;IRAZ;ERCIN, 2022;NEBEL;WRIGHT, 2000;OTTONI, 1996;OTTONI, 2022;OTTONI;SAMPAIO;VASCONCELOS, 2017;SILVA, 2015;WONG, 2022).
Fluviometric data were obtained from ANA (2023) corresponding to the fluviometric posts of Quizanga (on the Guapiaçu river) and Parque Ribeira (on the Macacu river) for the elaboration of hydrograms of floods from historical series available.The proposal for revitalizing the basins is presented, according to an analysis of the conditions of use and occupation of the soil, field visits at the places of interventions in the basin and data on hydrological monitoring, starting from the historical series available.

RESULTS AND DISCUSSIONS
The assessment of water availability in basins depends on the analysis of hydrological processes (COSTA et al., 2023) There are few flow measurements in the Guapiaçu and Macacu rivers available for the assessment of effective water availability in the region.From the fluviometric data of ANA (2023), at the fluviometric stations of Quizanga (on the Guapiaçu River) and Parque Ribeira (on the Macacu River) (Figure 6), hydrograms were elaborated from available historical series, as shown in Figures 7 and 8.According to the local concessionaire, responsible for the production of water for drinking water supply in the region, there is a current production of 6 m3/s in the Immunana-Laranjal system, with a demand of more 5 m 3 /s until 2030 (ENVIRONMENTAL ENGINEERING AND CONSULTING, 2013).The average flows at the 2 fluviometric outposts, Quizanga and Posto Ribeira, respectively, in the Guapiaçu and Macacu rivers (observed in the middle stretch, being thus a conservative assessment), correspond to about 15 m 3 /s (ANA, 2023), from the exutorium of the Guapiaçu and Macacu rivers, together in the Canal de Imunana.Accordingly, it can be admitted, under normal conditions, that this average flow meets the complementary demand of another 5 m 3 /s, provided that the environmental health conditions of the watersheds of these rivers are recovered, as shown in the scope of this work.From an assessment of the hydrological precipitation data that occurred in these river basins over 35 years of data available on ANA's website (2023), the high availability of rainwater defluviums in the region can be observed.This study foresees the recovery of the soil, the retention of rainwater in these pasture areas and the consequent increase in the capacity of the groundwater recharge (which would have a runoff coefficient of less than 0.3, that is, more than 70% of the rainwater would be retained in the water basins of the Guapiaçu and Macacu rivers, and would infiltrate into the soil as recharge water of the groundwater sheets in these selected pasture areas), which would mitigate the floods in the rainy periods, without jeopardizing the activity of livestock farming.A few hours after the rains, all the waters retained by the interventions proposed in the Project would be infiltrated into the soil, with the guarantee of the increase in the flows of these rivers in the periods of drought, where the increase in the flows of the Guapiaçu and Macacu rivers forecasts the proportional increase in the flows in the Canal de Imunana, besides the reinforcement in the water supply for the population, starting from the very capture of the existing concessionaire, without the need for new abstractions.As the average flow of a river section can be considered as the maximum regularizable flow (OTTONI, 1996;SILVA, 2015;SOUZA, 1979), it is noted that the periods of higher than average flow, corresponding to the annual river defluviums, are expressive, with floods that reach more than 120 m 3 /s in the Guapiaçu River and 220 m 3 /s in the Macacu River (ANA, 2) 023)  Depending on the conditions of occupation in the basin and the analysis of hydrological data, related to the history of the observed flows, the proposal to revitalize the basins of the Guapiaçu and Macacu rivers is considered: 1-Implementation of the Hydrometric and Water Quality Monitoring Program of the Guapiaçu and Macacu Rivers, and its main tributaries, covering at least 1 to 2 years of complete hydrology, in order to assess more accurately the degradation of the soil of these river basins affecting the regime of the rivers, as well as the sources of water pollution of occasional and diffuse origin, in order to adopt the measures and mitigating and corrective measures to recover the quantity and quality of the waters of these rivers.Ideally, this environmental monitoring should be carried out permanently throughout the work.With the instantaneous measurement of the flow and the quality of the water of the rivers in different hydrometric sections, one can also have a diagnosis of the pollution loads (flow of the river x concentration of pollutants) of the Guapiaçu and Macacu rivers and their main tributaries.The water quality parameters to be used will be those that are most relevant according to the type of water pollution in the region.Besides measuring river flows, it is intended to carry out rainfall and climatological surveys complementary to the current data, with a view to underpinning the hydrological studies for the region.All the changes that occur in the use and occupation of the land of the drainage basin have direct effects on the alteration of the flow regime and on the quality of the waters of the rivers; if these alterations are negative (deforestation, stripping and waterproofing of the soil, etc.) the regime of the rivers becomes more irregular (increasingly larger flows in the rainy periods, aggravating the floods, and the reduction of the river flows in the periods of drought, aggravating the problem of water scarcity, as happens today, besides the problem of degradation of the quality of the river waters) (NEBEL; WRIGHT, 200000000000000000000000000000000000000000000000000000000000000000000 0 2022a; SILVA, 2015;SOUZA, 1979).

2-
Preparation of Environmental Diagnosis of the basins of the Guapiaçu and Macacu rivers, based on the basic data collected in the previous stages, where it is intended to draw up the mapping of the hydrographic region under study, to define more precisely the real hydrographic network existing (due to the drastic changes made in the past by the DNOS with the channeling and rectification of rivers), the different types of use and occupation of the soil, and of degradation of water resources in these river basins, as well as the degraded areas of these river basins that are suitable for undergoing adequate environmental recovery interventions.

3-
Preparation of the Project for Applied Research of Works and Interventions with Environmental Sustainability aiming at the environmental recovery of the watersheds of the Guapiaçu and Macacu rivers as a whole, with a view to the expansion of the supply of water for the region of the east of Guanabara Bay.The different works and interventions to be designed for the environmental recovery of the watersheds of the Guapiaçu and Macacu rivers will take place as a priority in existing pasture areas in this region, without harming local farmers and therefore without generating losses of agricultural production in the region, which would harm the population of part of the state of Rio de Janeiro, which normally consumes these products in their daily food.These works and interventions of reforestation and recharging of underground water tend to produce positive impacts in the hydrographic basin, with an increase in soil humidity, and with more vegetation, will positively affect the hydrological regime of the Guapiaçu and Macacu rivers.This is how it is expected to reduce flooding during rainy periods, and the water retained in the form of underground feeding of the groundwater aquifers forecasts an increase in the minimum flow of these rivers and their tributaries during the dry season, so as to guarantee greater water security and better quality in the abstraction of water existing in the Canal de Imunana, operated by CEDAE.Within the program of activities provided for in the studies for environmental revitalization of the watersheds of the Guapiaçu and Macacu rivers, the intention is to carry out an evaluation of the implementation of the Water Producers Program in the region, in relation to the owners of these particular lands of the areas of reforestation interventions and works for the artificial recharge of implanted rainwater, owners who would come to participate in the solution for the recovery of the quality and quantity of the water of the river and its tributaries that make up this Pilot Basin.In the Water Producers Program, the owners of the land in the water recharge regions and springs of the natural water sources would receive money from the authorities responsible for the implementation of the corrective interventions of environmental protection in the river basin, and these landowners would participate in the activities of maintenance and permanent conservation of the whole environmental system, with adequate capacity and technical guidance from the authorities responsible for the implementation of the corrective activities in the basin, with the sustainable and integrated management of its waste, economic recovery of its land, and the increase of the quantity and improvement of the water quality of these water sources.This type of intervention is already being successfully carried out in the water sources that supply the city of New York, in the United States (GROLLEAU; MCCANN, 2012;HANLON, 2017), using Public Policies with Environmental Sustainability implemented by the responsible authorities.With regard to the subject, one should seek to make possible an integrated management in the management of sanitation in the watersheds of the Guapiaçu and Macacu rivers, as provided for by Law 12305 (BRAZIL, 2010), contained in the National Plan for Solid Waste (BRAZIL, 2022).For the city of Cachoeiras de Macacu, as the largest in the region, it is suggested to implant selective collection of its Urban Solid Waste (MSW), separation of dry and wet waste, as: the dry waste would go to the Sorting Plants to take advantage of dry recyclable material (glass, metals, plastics, paper and cardboard, etc.); the wet waste (where the remains of food are found) could be sent to a composting plant, to be transformed into organic compound, to be reused in agriculture and recovery of degraded soil (BERNAT et al., 20 22;CHEN;ZHANG;YUAN, 2020;KUNSZABÓ et al., 2022).Sustainable management of the city's sanitary sewage can include the solution of sewage collection and treatment, with the reuse of these treated sewage, where sludge retained in treatment could be directed to biodigesters (rather than being routed to garbage landfills) and be transformed into biogas and organic compost (AYDIN TEMEL, 2023;CHEN et al., 2022;KURODA et al., 2023).Integrated sanitation solutions, both for solid waste and for sewage, within the concept of environmental sustainability, can be directed towards the production of organic compost from organic waste and sewage, which is a fertilizer of excellent quality, and can be used to cheapen reforestation in the river basins of Guapiaçu and Macacu, where integrated sanitation of sewage and urban solid waste, besides reducing water pollution of rivers, would favor the production of fresh water in the river basins by the recovery of the humus of the soils from the reuse of the organic compost from waste and sewage (OTTONI, 2022nd, 2022b.
Figure 9 illustrates the estimated general conformation of the environmental revitalization actions of the Guapiaçu and Macacu river basins from the proposed actions of nature-based solutions.Estimates of the costs of setting up the works and the planned interventions are lower than the high costs and impact of the work of the Guapiaçu river dam originally proposed for the production of water for the eastern region of Guanabara Bay.The work showed that the originally proposed dam on the Guapiaçu river is likely to have a negative impact on the Guapiaçu river and that it does not guarantee the production of water in the basin, since the dam only accumulates in the useful volume of the reservoir the waters that run out of the river during the rainy periods, and regularizes the flow, as excess water extravasates during rainy periods through the spillage of these hydraulic works.The real production of fresh water is due mainly to the recovered and preserved river basin, which retains and infiltrates a large part of the rainfall waters into the soil, cushions floods and guarantees more water in the rivers during periods of drought, with cheaper works and interventions, and positive effects of environmental recovery and of improvement in the living conditions of the population, which is what is provided for in the studies and projects that we are proposing.Therefore, the present study for the Environmental Recovery of the Guapiaçu and Macacu River Basins, will aim to increase the water availability for water supply purposes of the eastern Guanabara Bay region.In periods of more vigorous rainfall, or in the expansion of the flow of water abstraction in fresh water for the region, the preserved watersheds of the Guapiaçu and Macacu rivers should allow an additional water supply, through the proposed interventions, that will be retained in greater quantity in the soil of these watersheds due to the greater recharge of the rainwater in the existing groundwater sheets in the catchment of these rivers, from fresh water sources of better quality and in greater quantity to serve the population of the eastern region of Guanabara Bay, in a sustainable manner, with the preservation of the soil and the natural ecosystem.If there is interest, later on, in complementing the actions of environmental recovery of the watersheds of the Guapiaçu and Macacu rivers proposed in this project, smaller and less impactful buses can be implanted than the dam in the Guapiaçu river initially forecast, with less environmental liabilities for the region.

Figure 1 -
Figure 1 -Schematic representation of slope works and actions in the flow regularization process Source: Ottoni (1996).

Figure 2 -
Figure 2 -Flow regulation, with increased artificial recharge of rainwater in the soil, reduction of floods and droughts Source:Ottoni (1996)

Figure 4
Figure 4 illustrates the water basins of the Guapiaçu and Macacu rivers and their displacement in the Canal de Imunana (OTTONI et al., 2019).

Figure 7 -
Figure 7 -Hydrogram of the existing annual historical series of the Quizanga outpost on the Guapiaçu River Source: The authors.

Figure 8 -
Figure 8 -Hydrogram of the existing annual historical series of the Parque Ribeira outpost on the Macacu River Source: The authors.

Figure 9 -
Figure 9 -Estimated overall conformation of the environmental revitalization of the Guapiaçu and Macacu river basins Source: Ottoni et al. (2019) Environmental Revitalization of the River Basins of the Guapiaçu and Macacu Rivers to Increase Water Security in the Eastern Region of Guanabara Bay, Rio de Janeiro-RJ ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.1 | p.1-21 | e04417 | 2024.