# Introduction his paper presents a general system for the reconstitution of mean monthly natural flows in watersheds to support the SNIRH (Brazilian acronym for National Water Resources Information System) in charge of the National Water Agency (ANA). The system, called SisVazNat (Natural Flow System), was developed in Delphi platform, because it has a better performance in the implementation of software for desktop environments and provides resources that allow the best graphic designs [1]. The need for system structuring is due to the fact that flows may suffer the influence of human modifications, which affect the natural flow regime impairing the assessment of water availability of a particular reach of a stream. In order to make a reliable assessment, it is essential to determine the so-called "natural flow series". The reconstitution of natural flow series demands careful analyses and procedures, among which the water balance stands out. In short, the method considers that natural flows are calculated from data of inflows that are turbinated and released from hydropower plants, water traveling time between those power plants and the arrangement of the set of power plants. Losses by evaporation of the flooded areas in each reservoir in relation to conditions that already existed before its implementation, a phenomenon called net evaporation, is also considered in this calculation. The particular objective of this project was to develop automated tools that facilitate the reconstitution of those natural flows. The software developed also allows the extraction of metric and topological information on the millionth scale. # II. # The New Brazilian Model of Water Resources Management Water resources availability and multiple uses as well as the conflicts that arise from their use, currently represent a major challenge for society. In this context, Brazil is facing the challenge of creating legal and administrative mechanisms to harmonize the use of water resources with sustainable economic and social development. The new model of water resources management is based on Law nº 9.433/97, which establishes the principle of multiple uses as one of the bases of the National Water Resources Policy to allow different user sectors the right of access to water. In order to establish this policy, the federal government created ANA which is entrusted with implementing the management tools, among which SNIRH stands out. SNIRH development is based on a strategy of joint construction, participatory and decentralized involving the federal and state spheres of the government. A monitoring network composed of gauging stations to provide continuous data, the so-called historical discharge series, is needed to characterize water supply. On the other hand, demand is obtained from an updated registry of users. The balance between supply and demand, which is called water availability, indicates the scarcity or abundance of water in a watershed. Characterizing water availability and T determining its relationship with current and future demands is crucial to define the rules for the allocation of water resources among different users [2]. Thus, the historical discharge series are essential data for water resources management. However, stream flows are affected by human modifications such as dams, irrigation, withdrawals for human, animal or industrial supply. The consumptive water uses can affect the natural flow regime impairing or even preventing the correct evaluation of water availability. Thus, it is important to determine the "natural flow series" i.e., those that occurred before human actions. This process receives the name of reconstitution of natural flow series. # III. # System Structure The SisVazNat was structured into five modules: SisVAP, SisPEx, SisEL, SisReNat and SisUSO. Fig. 1 shows the interconnection between the SisVazNat modules for the natural flow series reconstitution process. Given the huge amount of data, the separation per hydrographical unit was chosen for the incorporation of the integrated hydro reference base on a 1:1.000.000 scale, provided by ANA. Each project corresponds to a basin or sub-basin in national territory, as shown in fig. The hydro reference methodology is based on the concept of segmentation of incremental basins, which is defined from the difference between the surrounding drainage areas of each pair of successive points of interest located in a certain section of the river, for example, "P1" and "P2" points in fig. 4. The calculation of the surrounding areas of each point of interest was defined from the sum of all basin areas upstream of the section which contains the point, added of the area directly proportional to the ratio between the distance from the beginning of the section up to the point and the total length of the section. It allows the user to visualize the gauging stations, as well as the data availability period within a certain river basin, fig. 6. In addition, it is possible to select the stations of interest, and import, partially or completely, the discharge series, being only necessary that the user types the dates of beginning and ending. This option was created to help the user in deciding which base stations may be used for gap filling and/or series extension. The automatic gap filling and/or extension may be done through: ? Relationship between drainage areas: Developed to be used, at least, between 2 stations, one of which serves as a base, located in the same water course or the same basin, and the other which has its gaps filled and/or extended. ? Multiple correlations: It is a generalization of the relationship between drainage areas where the user may define the multiplier coefficients of the base stations, and where the use of more base stations for filling and/or extension of flow gaps is possible. ? Linear regression: Forecasted to be performed between one or more base stations and that which will be filled and/or extended, as shown in the example in fig. 9. # Fig. 9 : Linear regression equation When the user clicks the button "Executar", the values for gap filling and/or extension of the series of the gauging station shall be automatically calculated. In addition to the tabular output, fig. 10, the SisPEx allows the user to verify, through a summary board, from the complete series of the station, the number of months that were filled and/or extended, how many could not be filled ("Valores indeterminados") and the number of The water balance of the reservoirs formed by the hydropower plants is a function of the net evaporation loss during a period of time (EL). The net evaporation loss, as defined by [3] is the difference between the evaporation from the reservoir and the evapotranspiration from the reservoir site (before the reservoir formation). In the scenario prior to the lake formation, there is ground cover which demands water for its needs, named effective precipitation. According to [4], the effective precipitation corresponds to the precipitation share stored in the influence zone of the cultivated roots and available for them to fulfill their demands. In this way, the effective precipitation (Pe) is the share of total precipitation (P) which does not flow superficially nor runs off below the root zone of said vegetation, and can be calculated through the USDA method below, according to [5], by the following equations: , for P>250 mm (2) Besides, in this situation, the vegetation transpiration process and soil evaporation in its surroundings, named real evapotranspiration (ETR), which corresponds to the amount of water the atmosphere can effectively remove from the soil-plant system must be taken into account. To calculate it, the SisEL allows the user to choose between the formulation proposed by [6] and the CRAE model from [7]. As the method from [6] is a function of the potential or referential evapotranspiration (ETo), SisEL allows the user to estimate ETo through the Penman-Monteith [8], Hargreaves-Samani [9] and Blaney-Cridle [10] methods. The processes which govern the scenario after the lake formation are precipitation and lake evaporation, once there is no more ground cover nor, consequently, the effective precipitation and actual evapotranspiration processes. In this case, the phenomenon may be represented by: ETR - ELa = EL(3) Where: ELa is the lake evaporation; and ETR the real evapotranspiration before the implementation of the reservoir. The lake evaporation may be calculated through the Linacre [11], Kohler et al [12] and Morton CRLE model methods, or yet through class A tank. The fourth module is the SisReNat, which allows automatic generation of the monthly natural flow series from a particular point of interest located in a certain river reach. The calculation of the monthly natural flow series for any point in the hydrographic network may be performed in three different ways: entering the name of the hydropower plant, clicking on the hydrography or entering the coordinates of the point of interest. If the point of interest defined by the user is a hydropower plant, the system will use Eq (8) for calculating the natural flow series. Otherwise, the natural flow is calculated from the transferral of the inflows to a hydropower plant located on the same river reach or, in case of lack thereof, from the transferral of the gauging station discharges located on the same river of a nearby basin. In both situations, the transference process is done based on the relationship between drainage areas. In case of a hydropower plant, the value transferred corresponds to the difference between the natural flow (estimated through Eq ( 8)) and the consumptive water use at the location of the plant, and the result is added of the consumptive water use at the point of interest. In a similar manner, in the case of gauging stations, the consumptive water uses are added up after the transference of the observed gauging station flows to the point of interest, Eq ( 9) and (10). For the calculation process, the system informs which the hydropower plants (fig. 12) or gauging stations (fig. 13) are on the river reach or basin where the chosen point is located, as well as the availability of operational data and/or series of historical discharges of the selected period. Finally, once the hydropower plant or gauging station is selected, the SisVazNat automatically generates the natural flow at the point of interest defined by the user and presents the natural flow series for the chosen period, as shown in fig. 14. # Methodology The method adopted by [13] in the reconstitution of the natural affluent flow of the hydropower plants is the reservoir water balance. The natural flow of each hydropower plant is obtained from the application of the following expression: Qinc Qnatp Qnat + =(4) Where: Qnat is the natural flow at the location of the selected hydropower plant; Qnatp is the natural flow at the upstream reservoir(s); Qinc is the natural incremental flow between the selected hydropower plant and the upstream hydropower plant(s). The flow of the incremental basin related to each hydropower plant (incremental natural flow) is calculated from: Qdiv Qevp Quse Qrel - Qinf Qinc + + + =(5) Where: Qinc is the incremental natural flow, between the selected hydropower plant and the upstream hydropower plant(s). Qinf is the inflow to the selected hydropower plant reservoir; Qrel is the released flow of the upstream reservoir(s); Quse is the flow related to the consumptive uses of the incremental basin; Qevp is the flow related to the net evaporation; Qdiv is the flow diverted in the incremental basin, through channels, tunnels or bombing station. The flow related to net evaporation is expressed by: + ? + ? + ? + ? ? = 3 3 2 2 1 0 6 h A h A h A A [ 10 2,6298 EL Qevp 1000 ] h A 4 4 ? ? +(6) Where: h is the reservoir average stage; A 0,1,2,3,4 are the coefficients of the stage-reservoir area equation; 2,6298.10 6 is the number of seconds in a month. The value of the diverted flow shall be accounted on the flow related to the consumptive uses of the incremental basin. Based on this, Eq (6) may be rewritten as follows: Qevp Quse Qrel - Qinf Qinc + + = (7) The general equation of the natural flow in a hydropower plant "i" can then be expressed as: ( ) + ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? + = = = i n 1 j j n 1 j j j i i Quse Quse Qrel inf Q inf Q Qnat ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? + = i n 1 j j Qevp Qevp(8) Where: ( ) ? ? ? ? ? ? ? ? = n 1 j j j Qrel inf Q is the sum of the Sisvaznat: Natural Flows Reconstitution System as a Support for Water Resources Management difference between the inflows and release flows of the set of hydropower plants located upstream of the hydropower plant "i" (it corresponds to the "Ret" column in fig. 14 ); ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? = i n 1 j j Quse Quse is the sum of the incremental consumptive uses of the set of hydropower plants located upstream of the hydropower plant "i", including itself; ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? = i n 1 j j Qevp Qevp is the sum of the net evaporation flows of the hydropower plants reservoirs located upstream of the hydropower plant "i", including itself. For the generation of the monthly natural flows in streams where there are no hydropower plants, the mean monthly flow data from the gauging station(s) upstream or downstream from the point of interest is used, transferred by relationship between drainage areas, added of the consumptive uses accrued up to the point of interest. The equation for the reconstitution of the monthly natural flow from the observed data is expressed as: i j i j i Quse A A Q Qnat + ? ? ? ? ? ? ? ? ? = , i downstream from j J i i j j i Quse A A Q Qnat + ? ? ? ? ? ? ? ? ? = , i upstream from j (10) Where: Q j is the mean monthly average discharge at the gauging station located at point "j"; A i is the drainage area surrounding the point of interest "i"; A j is the drainage area surrounding the gauging station located at point "j"; Quse i is the accrued monthly consumptive uses up to the point of interest "i". In case of lack of gauging stations on the river reach, in which the point of interest "i" is located, the option of transference is granted to the user, through the relationship between drainage areas, from the gauging station(s) located on nearby basin(s). In case the hydropower plant does not possess operational data, it shall be considered by the SisVazNat as a point of interest and the monthly natural flow is estimated from Eq (9) or (10). V. # Results The SisVazNat was applied in the Tocantins basin located in the Amazon Region. The basin has a drainage area of 767,000 km 2 , or about 7.5% of the Brazilian territory. The geographic coordinates used to locate the operating hydropower plants in the basin are shown in Table 1. * UHE is the Brazilian acronym for hydropower plant. In order to validate the proposed methodology we considered the year of 2003 (January to December) for the simulations using the Morton model, and the results found were compared to the series of natural flows published by ONS. The choice of the Morton model sought to match the simulation of the SisVazNat to the criteria adopted by ONS regarding the generation of natural flows. The differences are shown in Tables 2 to 5. # Conclusion The mean percent differences between the results obtained with the SisVazNat and the monthly natural flow series consolidated by ONS in each hydropower plant were, respectively: UHE Serra da Mesa (3.2%); UHE Cana Brava (5.6%); UHE Lajeado (4.2%) and UHE Tucuruí (4.4%). These small differences allowed the validation of the tool. The application of the system to the case study was successful generating natural flows similar to those established by the electrical sector in Tocantins river basin. Thus, it is possible to infer that SisVazNat meets the proposed objectives, since it operates in an interactive way with the user, allowing frequent data updating, generating natural flows in any point of a watercourse in the Brazilian territory. The system may be used as a supporting tool that can help Governmental agencies, because it supplies an adequate representation of the water availability in a scenario that existed prior to human modifications in the basin allowing the water resources manager to use the natural flow series to define the criteria for a better allocation of water among multiple users. The application of the SisVazNat to other Brazilian watersheds is recommended for future developments. 1![Fig.1 : Interconnection between the SisVazNat modulesSisVAP is a tool for editing and selecting the basin which contributes to the point defined by the user, as well as, from the local database, associating with the existing climate, gauging and raingauge stations and hydropower plants on the selected basin. Its objectives are:](image-2.png "Fig. 1 :?") 2![As an example, fig. 3 presents the Tocantins river basin, located in the Amazon Region. Current and forecasted hydropower plants, climate, gauging and raingauge stations are presented in this figure.](image-3.png "2 .") 23![Fig. 2 : SisVazNat start screen](image-4.png "Fig. 2 :Fig. 3 :") 4![Fig.4 : Incremental areas for P1 and P2 points of interestThe SisVAP allows the user to visualize the contributing basin of the river sections and identify and locate the raingauge, climatic and gauging stations, and the hydropower plants upstream of the selected point. In addition, the lengths of the reaches and the drainage areas to the point selected by the user are provided, as shown in fig.5.](image-5.png "Fig. 4 :") 5![Fig.5 : Incremental basin segmentation located upstream of a point of interest The second module is SisPEx, which was built for automatic filling and extension of the mean monthly average discharges series in each gauging station. Its main objectives are: ? Allowing the management of gauging station database registries of mean monthly discharges. ? Visualization of the registries (graphs and tables). ? Extension or gap filling the discharge series by linear regression or relationship between drainage areas or multiple correlations.](image-6.png "Fig. 5 :") 6![Fig.6 : Station Selection for Filling and/or Extension of Flow Series](image-7.png "Fig. 6 :") 7![Fig. 7 : Mean discharge hydrograph](image-8.png "Fig. 7 :") ![months of observation for a certain station ("Valores consolidados"), fig. 11.](image-9.png "") 10![Fig. 10 : Filling results tabulated values](image-10.png "Fig. 10 :") 11![Fig. 11 : Filling results summary board The third module is the SisEL, which allows visualization of climatic data (temperature, wind velocity, evaporation, rain, sun exposure and humidity) and the insertion of new information. It calculates the climatic variables involved in the natural flow series generation](image-11.png "Fig. 11 :") 12![Fig. 12 : List of hydropower plants located within the same river reach of a point of interest](image-12.png "Fig. 12 :") 13![Fig. 13 : Gauging stations located on the river reach or basin of a point of interest](image-13.png "Fig. 13 :") 14![Fig. 14 : Natural flow series generated at a hydropower plant location](image-14.png "Fig. 14 :") 1Hydropower Plant*LatLongDrainage Area (km 2 )UHE Serra da Mesa-13.827 -48.30751,233UHE Cana Brava-13.407 -48.14258,022UHE Lajeado-9.756-48.374183,718UHE Tucuruí-3.833-49.647757,577 2DateNatural Flow (m³/s) ONS SisVazNatDifference (%)Jan-031,197.01,142.44.6Feb-031,056.01,068.91.2Mar-031,140.01,138.90.1Apr-03919.0917.40.2May-03425.0415.62.2 3DateNatural Flow (m³/s) ONS SisVazNatDifference (%) © 2012 Global Journals Inc. (US) * Sisvaznat: Natural Flows Reconstitution System as a Support for Water Resources Management Jun-03 * Table 5 : Results obtained in UHE Tucuruí Date Natural Flow (m³/s) * References Références Referencias * AFHora Hora * SisVazNat 1.0: Sistema de Reconstituição de Séries de Vazões Naturais MA G MMarques E 2010 75 1ª edição * Compatibilização da geração de energia em aproveitamentos hidrelétricos com os demais usos dos recursos hídricos MA GHora 2012 112 Editora da UFF, 2ª edição * Reservoir Capacity and Yield TMacmahon RGMein 1978 Elsevier Scientific Publishing Company 213 * Soil Conservation Service, United States Department of Agriculture. Part 623: National Engineering Handbook Usda-Scs 1993 Chapter 2: Irrigation Water Requirements * CROPWAT. A computer program for irrigation planning and management MSmith Irrigation and Drainage FAO -Food and Agriculture Organization of the United Nations 1992 Paper nº 46. 126p * The water balance CWThornthwaite JRMather Publications in Climatology Centerton, NJ 1955 104 Drexel Institute of Technology -Laboratory of Climatology * Operational Estimates of Lake Evaporation FIMorton Journal of Hydrology 114 Oct. 1983, v.66 * FAO "Crop Evapotranspiration (guidelines for computing crop water requirements)". In: Irrigation and Drainage FAO -Food and Agriculture Organization of the United Nations 1998 Paper nº 56. Available at * Estimation of potential evapotranspiration GHHargreaves ZASamani Journal of Irrigation and Drainage Division ASCE 108 1982 * FAO "Irrigation Water Management: Irrigation Water Needs". In: Irrigation Water Management -Training manual nº FAO -Food and Agriculture Organization of the United Nations 1996 3 Paper nº 24. Available at * Data-sparse estimation of lake evaporation using a simplified Penman equation ELinacre Agricultural and Forest Meteorology 64 1993 Elsevier * Evaporation from pans and lakes MAKohler TJNoredenson WEFox 1955 21 U. S. Weather Bureau Research Paper 38 * Módulo 23 -Critérios para Estudos -Submódulo 23.5 -Critérios para Estudos de Hidrologia Operacional ONS ONS -Operador Nacional do Sistema. 11p. Julho de