TAXES SIMULATION FOR MAINTANCE OF A DRAINAGE NETWORK

Purpose: The objective of this work was to evaluate methods of charging urban drainage fees in order to finance and guarantee the maintenance and operation of a drainage network in a residential subdivision located in the city of Rio de Janeiro. Theoretical framework: The intense urban growth associated with the process of soil sealing in urban areas has caused, over the years, the increase in occurrence and intensity of disasters related to floods, in order to reduce the capacity of urban drainage systems to guarantee their optimal functioning. Method/design/approach: The methodology of this study used three different methods to calculate a drainage rate, through a classification of land use and occupation and maintenance values for the drainage network, as: Equivalent Residential Unit (URE), Tucci method (2002) and Cançado, Nascimento and Cabral method (2005). Results and conclusion: The values presented by the methodology entitled Equivalent Residential Unit reached the objectives and the method was selected with the determination of the impact generated by the possible collection of this fee, through data from the 2010 Census. The drainage network per lot were R$262.35 per year, with a total collection of R$24,398.49, compatible with the values found for maintenance of the drainage network in the allotment in the city of Rio de Janeiro-RJ, with an average impact of 0.70% on the income of users of this service. Research implications: The main contribution found by this study was the analysis of the economic and financial viability of the allotment users regarding the collection of a fee for maintenance and operation of the drainage system. Originality/value: This article proposes to present a fee that can finance the maintenance of the existing drainage network, in order to mitigate the effects of flooding on the site and eliminate the financial impact of this service on public coffers.


INTRODUCTION
The increasing increase of soil sealing in urban areas, coupled with the increasing migration of the population from the countryside to urban centers, contributed to disorderly growth in these areas.The increase in the rate of waterproof area directly impacts the volume of infiltrated water, as well as the volume drained.Thus, the increase in frequency and intensity of extreme events has a direct impact on the recurrence of flooding in urban centers (Aich et al., 2015).

Justification and Search
Flood events in urban areas become increasingly frequent, taking into account the changes in land use and occupation of urban areas, climate change and the maintenance of the implanted drainage systems.The year 2021 presented a total number of 432 disasters reported, with flooding being the most frequent event, with a number of 223 occurrences, demonstrating a number even above the historical average of the years from 2001 to 2020, which is 163 events per year.In the year 2021, events related only to floods caused financial losses amounting to 74.4 billion dollars, higher than the annual average of 34.1 billion dollars per year (CRED, 2021).In financial terms, a study by Ogie et al (2018) shows that without any technical action in this area to reduce flooding, the financial damage would reach USD 1 trillion by the year 2050.

THEORETICAL FRAME
The control and management of urban rainwater and disasters, related to this service, becomes paramount and of extreme importance.The solution for mitigating the impacts and reducing the disasters caused by floods cuts across technical, social and financial areas and uses scientific resources, such as the basin study and operational aspects aiming at efficient maintenance of the drainage system (Bryndal et al., 2017).
In a study conducted by Rocha (2021), the author discusses the reasons that relate urban mobility to disasters, including the floods in the city of Campos.The author presents that the great flood of 2008 mobilized 22,662 with the disaster related to the flood.Also according to this study, in the city of Uruaí, 81.5% of the domiciles studied have already undergone flooding at least once.
Some of the various concepts are among the most widespread on issues related to urban drainage and its connection with disasters on these systems.A study by Karamouz and Zahmatkesh (2016), resilience is in retaining a certain level of service during flooding.The authors used multi-criteria decision-making methodology that determine flooding in coastal cities.
In a study conducted by Paes et al. (2020), the authors point out that a determining factor for understanding public purchases is the way we interpret national legislation within strategies at local levels.The authors also reinforce the fact that the regional plurality of the Brazilian territory directly affects the way legislation is applied depending on the region.
Due to the lack of budget with specific destination for the urban drainage system and its maintenance, Brazil, as well as several countries, make use of municipal taxes and eventually state or federal investments for the realization of the operation of the urban rainwater system (Tucci, 2002).
Although there are no records of specific federal investments in order to promote the urban rainwater system, according to the National Sanitation Information System (SNIS), 24 Brazilian municipalities (out of a total of 4,107 registered municipalities) report to carry out some kind of charge or charge for the service of urban rainwater management (SNIS,2021).
Therefore, reaching less than 1% of the municipalities informed, even provided for in Law 11.445/2007, in its Article 29, paragraph III, and in Article 36, paragraphs I and II, the mechanism of collection is embryonic in the country.Of the 24 municipalities cited, there are values that surround R $ 31,11 monthly per property, among these, 11 municipalities report to use a fee or public price, while 13 municipalities report to carry out this charge through specific tax (SNIS,2021).
The difficulty of implementing a charge on maintenance and operation services encounters social and political barriers, since the charges must be fair, equitable and based only on the costs of maintenance and operation of rainwater drainage systems.The implementation of this instrument requires a joint effort between technical, political and legal parties, and presents itself as an important way to obtain resources for maintaining the system (Tasca et al., 2017) Urban rainwater drainage has characteristics of public goods, such as non-exclusion and non-rivalry of actions.Thus, this indicates that it is not possible to exclude an agent from its respective consumption, in other words, when a due service is offered, all who can, or will, obligatorily enjoy the service, as is the case of the maintenance of the drainage network.Therefore, depending on the obligation to use services, from a legal point of view, the appropriate thing would be to charge a fee on the users, aiming at the maintenance of the system (Cancido et al., 2006).
The collection of a fee as a management tool is dealt with in a amplified manner when analyzed in countries where this instrument is widely used.A study by Campbell and Bradshaw (2021) in the United States found 2,057 rainwater dealers located in 41 states and the District of Columbia, as well as 62 in Canada.
The values found by Campbell and Bradshaw (2021) present an average of 6.01 USD (31.65 BRL)4 monthly, with standard deviation of 4.69 USD (25.37 BRL).The authors found, as the most used methodology, the Equivalent Residential Unit, which contemplates the impermeable portion of each family unit to make up an average charge on the lot.In Canada, the average values found by the authors were 11.62 USD (61.19 BRL), with the methodology employed also being the Equivalent Residential Unit (ERU).
According to Valiron and Tabuchi (1992), the city of Munich, Germany, is showing a rainwater charge.The value found by Chouli et al. (2007) is fixed at approximately USD 1,17 (BRL 6,16)5 per square meter of impermeable area, which corresponds to the amount charged for the sanitary depletion in the city.
Australia is known as an example in urban drainage management and despite this, drainage rates are poorly cited, making it feasible for the country's environmental committee to recommend research funds in this area to be resumed (Australia ,2015).
The City of Melbourne charges a storm water management fee for residents who are in areas served by the city's drainage system.The values were modified in 2020 from a reshuffle in its payment system.Fees, levied annually range from 24.62 AUD (87.68 BRL)6 for lowimpact residences smaller than 200 m², to 5,107.59AUD (18,195.79 BRL) for non-residential areas larger than 45,000 m².However, it is important to note that the city applies various incentives for those who own and use rainwater retention systems on their property (Sydney Water, 2021).
In Brazil, despite the absence of specific legislation for the collection of urban drainage rates, the city of Santo André has adhered to a rainwater rate, among other studies developed by Tasca (2016), Tucci (2002) and Cancido et al. (2006).According to SNIS (2019), the city of Santo André charged the average value of R$2.20 per month per building, in a set of 219,117 units, corresponding to 98% of the properties in the municipality.Through this charge, the city raised in the year 2019 was R $ 5.780.729,30,while the expenditure reported for the maintenance of this service was R $ 43.226.893,38,ie, presents an annual deficit of approximately 87% (SNIS, 2019).
According to the National Sanitation Information System (SNIS), nationwide in the year 2020, of the 4,107 municipalities that participated and sent information 1,859 municipalities reported having an exclusive rainwater drainage system, 491 report having a mixed system and, only 876 reported having a combined system of rainwater and sewage management (SNIS,2021).
The solution proposed by Tucci (2002) used as a basis two (2) methods: the apportionment of indirect costs, related to the maintenance and operation rates of the system, and the apportionment of direct costs, corresponding to the rates of the implementation costs of the drainage works.The study carried out by Tucci (2002) proposes the unit calculation of the costs of the impermeable areas of the basin, considering that the volume disposed of in an impermeable area is about 6.33 times greater than the volume disposed of in the permeable areas.
A study conducted by Cancido et al. (2006) used the methodology based on waterproof area, justifying that waterproofing of the drainage area is the main factor affecting an urban drainage system, besides the fact of ease of understanding by the users of the plots.The simulation of the drainage rate in Belo Horizonte did not take into account a real case, but used the costs of maintenance of the drainage network used in the city (Cancido et al., 2006).
The costs of a drainage system are addressed and obtained by different methodologies.A study by Cruz (2004) used the city of Porto Alegre-RS, with the aim of reducing the costs of the municipality.Also according to the author, the total cost for seven basins was 1.4 billion reals, and according to the author the value used as the cost for the maintenance of the network was approximately 5% of the implementation value per year.

METHOD
The project is presented through the flowchart (Figure 1), composed of steps that aim at the main objective of simulating a fee that finances the costs of maintenance and operation of the network.
The selected study area is in the neighborhood of Jacarepaguá, in the city of Rio de Janeiro-RJ determined as a regular allotment, with consolidated urban drainage infrastructure and implanted through a cadastre of the current drainage network available at the Foundation Institute of Water of the Municipality of Rio de Janeiro (RIO-ÁGUAS, 2019).The location of the study area is at latitude 22°54'55.99"S,and longitude 43°23'48.51"O,with a distance of 3.32 km from the nearest rainfall station, Jacarepaguá/Tanque -14, operated by the Rio Alert System, of the City Hall of Rio de Janeiro.The rainfall index of the historical series analyzed between 1997 and 2020 was 1,068 mm annual average, or a monthly average precipitation of 89.7 mm (ALERTA-RIO, 2022).
The stage of characterizing the use and occupation of the soil was obtained from the geoprocessing of satellite images.The study used supervised image classification, with the selection of pixels as models and characterized in the map, with statistical treatments by the QGIS tool, used for the selection of probability of occurrence of each pixel in the studied image (Table 1).
According to the National Institute for Space Research (INPE), through its geoprocessing manual, it is necessary to identify an area that is completely homogeneous and that represents each class of use and occupation for the possible determination of its area.The representative areas thus define the class scattering diagram, as well as its probability of occurrence (INPE,2016).
The spatial sampling of the area used found exactly 1050 polygons, which represent the 5 use and land cover classes determined in the study, in which the permeability information in each polygon is to be removed.In the universe of the samples of class and land cover, the categories determined as "Paths and Sidewalks", "Mixed Buildings", "Single Family Buildings", and "Leisure Areas" had to be relocated in order to minimize errors and delimit a number of acceptable classes.The results obtained were evaluated by means of sampling.The technique used seeks to compare selected random points, with the points used within the "raster" file, and thus identify the pixel similarity.After creating selected random points in the software itself, which generates different points within the selected location, 540 different evaluation points were obtained.
After the selection of points, the information relating to the selected points was removed in the software itself, using its own tools called "Extract Values".Therefore, with this information removed, an evaluation based on the data taken from the "raster" file was carried out and thus performed the comparison and demonstrated in table 2. The average error margin found was 1.2% and the errors found are due to shading and pixels of the images that do not clearly appear in the original satellite image.
The allotment used in this study was obtained from the technical register existing at the Rio-Águas Foundation, with location located at the Boiuna Road, and residential lots registered in the Parceling and Allotment Project (PAL) number 25.285, which was replaced by the project number 30.065.After searching and detailing the existing lots, 107 lots belonging to the cadastre were identified.However, of the 107 batches studied, a total of 87 batches capable of generating the contributing surface run-off to the local drainage network were included.
Identification of contributing lots and land use and occupation information, combined with an overlay of layers, was carried out in order to obtain the sealing rate of each lot concerned.The image (Figure 2) demonstrates the overlapping layers, and it is also important to note that the batch called "Recreation" generates a contribution to the network in question, but has no payer.In this way, the collection of the lot in question was carried out using the same methodology as that applied to all lots, but its value was divided equally between the remaining lots.
The amounts to be financed by the collection of this fee are the amounts referring only to the service of maintenance of the drainage system.In a study carried out by Cruz ( 2004), these figures are close to the annual amount of 5% of all the value used for the implementation of this network.Therefore, the values used in this article are based on a study conducted by Coelho (2022), in which the author points to a value of network deployment of R$487,969.86based on June/2021.It is concluded that the fee to be found in this article should reach the amount of R$24,398.49,referring to 5% of the value of the implantation.The methodology used to calculate the collection in this project will be determined after the use of three different collection methods, the method called Residential Equivalent Unit (ERU), the method determined by Tucci (2002) and the method developed by Cançada, Nascimento e Cabral (2005).Therefore, for the development of the first methodology, called ERUs, considered a fair methodology with several variations, it uses the impermeable area of the batches for development.Equation 2 presents the rate of sealed area per lot, considering the sum of the impermeable areas of the lots and the total number of contributing lots.The calculation of the quantity of residential equivalent units of each lot is demonstrated as the waterproof area of this lot, used according to the waterproof rate calculated above (Equation 3).The methodology is a way of dividing the maintenance costs by the lots that contribute to the drainage, from their impermeable area.Therefore, the values to be costed, are the values found for local maintenance, divided by the amount of contributing lots (Equation 4).Therefore, the rate of each lot is calculated by the product of its unit rate and its quantity of corresponding ERUs (Equation 5).
The methodology defined by Tucci (2002) presents two costs for the definition of the costs to be financed by the collection.The costs to be financed can be direct and indirect, with the direct costs being the costs responsible for the implementation of the drainage system and the indirect costs being those based on the maintenance of the system.In this article we will only use the indirect cost methodology, as it is only the comparison of values responsible for this service.
The study carried out by Tucci (2002) considers parameters that can or cannot be modified, according to the area of the study used, for example, the volume discharged from impermeable areas is 6.33 times greater than the volume generated by permeable areas, and also the distribution of public areas as 25% and private areas as 75%.
According to Tucci (2002), the value of the unit cost of impermeable area is calculated through the total cost of operation and maintenance, the impermeable area of the whole basin and the total area of the basin (Equation 6).
After the calculation of the waterproof basin area unit cost, it is necessary to calculate the individualized annual rate per lot.The individualized batch calculation is performed by Equation 7, and uses the lot area and the waterproof percentage of the lot in question.According to Cancido, Nascimento and Cabral (2005) the cost per square meter of impermeable area is given by Equation 8, and unlike Tucci (2002) and the EBU methodology, 10 suggest that each lot has only one income that is responsible for bearing the cost of the drainage fee, by not finding data source that demonstrates the amount of residences or payers within each lot.In a study conducted by Tasca (2016), the impact of the rate can be considered high when above 0.45%, average oscillates between 0.45% and 0.22% and low when below 0.22%.
The challenge in the assessment of the average income per person responsible refers to the quantity of residences within each batch of the study.There is no data source that demonstrates the amount of residences within each lot, and therefore the impact of the fee was considered as each lot containing a residence, and an income.

RESULTS AND DISCUSSIONS
The financing of the maintenance of the drainage system in this plot, from the collection of a drainage fee in the methodology used in this study, is directly related to the contribution that this plot has to the functioning of this network.The implementation of the existing methodology presented the values found in a summarized form, in Figure 4, for the three methodologies.It is important to point out that the prorated values of the lot called "Recreation" are already included, and that the impermeable area of the lots is directly proportional to the amount charged by the fee.The mean values found according to the batch can be seen in table 03.Therefore, according to the ERU methodology, the proceeds obtained in this simulation were R$ 24,398.49,which are values equal to the values necessary for the maintenance and operation of the network annually.It is important to demonstrate that charging the levy in this way does not generate a budget deficit, which would lead to a withdrawal of other taxes in order to reach the budgeted value, but also does not generate a surplus, which demonstrates a concern with charging a fair levy only for performing the maintenance of the network, and therefore the methodology chosen was the URE.The values referring to income of persons responsible for the residence that were previously R$ 1,690.56monthly reais, within the census sector of the building lots under study, were corrected according to the IPCA index, for showing an updated and reliable index, with a comprehensive historical series, which reaches years since 1980.Table 04 shows the corrected values and indexes.The fee charged for the ERU methodology found in the lots represented an average of 0.62% in the income of the lots studied, with maximum values of 1.56%, and minimum values of 0.06%, and increases as the increase in the impermeable area, that is, the greater the impermeable area of a lot, the greater its drainage rate (Figure 5).

FINAL CONSIDERATIONS
Based on the results obtained from simulations for rates of three (3) models with the aim of financing the maintenance of a local drainage system, it can be concluded that: The methodology selected was that of the Equivalent Residential Unit (ERU) because it proved to be the most appropriate as regards the amounts charged to the users of the building lots, so as not to burden the public coffers in the maintenance and operation of the drainage system.
The average monthly rates obtained of R$ 21.86 per lot were considered sufficient in the guarantee of the costs of maintenance and operation of the drainage system without the deduction of other municipal and possibly federal taxes.
This study indicates for future work the need to draw up a record of the amount of savings that can pay for this charge in a single batch.A detailed analysis of the data on the use and occupation of the soil is also fundamental, using well-established techniques for geoprocessing satellite images.

Figure 2 .
Figure 2. Overlapping lots with land use and occupation.

Figure 4 .
Figure 4. Batch rate values in all three methods.Source: Prepared by the authors (2022)

Figure 5 .
Figure 5. Impact of drainage rate related to waterproof area.Source: Prepared by the authors (2022)

Table 1 :
Supervised classification of samples.Returns

TRUE on success or FALSE on failure. Area (m²) Number of polygons found (unit) Percentage of area obtained by polygons Samples
Source: Prepared by the authors(2022)

Table 2 :
Assessment of the sampling result

Table 3 :
Comparative values for the three methods used

Table 4 :
Values and indices for income correction

Corrected value at end date R$3,465.12 Source:
Prepared by the authors(2022)