INTEGRATED MANAGEMENT OF LANDBASED ACTIVITIES IN THE SÃO FRANCISCO BASIN PROJECT ANA/GEF/UNEP/OAS
Subproject 4.3 - Quantification and Assesment of the Efficiency of Water Usage by Agriculture in the São Francisco River Basin
Executive Summary of the Final Report
QUANTIFICATION AND ASSESSMENT OF THE EFFICIENCY OF WATER USAGE BY AGRICULTURE IN THE SÃO FRANCISCO RIVER BASIN
UNIVERSIDADE FEDERAL DE VIÇOSA Departamento de Engenharia Agrícola
Viçosa – MG
INTEGRATED MANAGEMENT OF LANDBASED ACTIVITIES IN THE SÃO FRANCISCO BASIN PROJECT ANA/GEF/UNEP/OAS
Subproject 4.3 - Quantification and Assesment of the Efficiency of Water Usage by Agriculture in the São Francisco River Basin
Executive Summary of the Final Report
QUANTIFICATION AND ASSESSMENT OF THE EFFICIENCY OF WATER USAGE BY AGRICULTURE IN THE SÃO FRANCISCO RIVER BASIN
Technical Coordination Coordenador: Márcio Mota Ramos Coordenador Adjunto: Fernando Falco Pruski Suely de Fátima Ramos Silveira - UFV Demetrius David da Silva - UFV Lineu Neiva Rodrigues – OEA
Consultants Wallisson da Silva Freitas Sérgio Oswaldo de Carvalho Avellar Alessandro de Freitas Teixeira Gessionei da Silva Santana Rafael de Almeida Ribeiro Nori Paulo Griebeler
January 2003
QUANTIFICATION AND ASSESSMENT OF THE EFFICIENCY OF WATER USAGE BY AGRICULTURE IN THE SÃO FRANCISCO RIVER BASIN
EXECUTIVE SUMMARY
INTRODUCTION In the elaboration of the “Integrated Management of Land Based Activities in the São Francisco River Basin Project - GEF/ANA/OAS/UNEP, also known as the GEF São Francisco Project, irrigation was identified as responsible for the consumption of approximately 70% of the water diverted from the São Francisco, which could be affecting the availability of the resource. Even though the irrigated area in the Basin is still small, corresponding to less than 10% of the irrigable area, they are concentrated in regional poles. Besides this, there are evidences that irrigated agriculture in the Basin presents a really low efficiency. These facts led to the inclusion of Activity 4.3 (Quantification and Assessment of the Efficiency of Water Usage by Agriculture in the São Francisco River Basin) in the São Francisco Project. The Activity was implemented with donation funds provided by the Global Environmental Facility – GEF and was implemented by the United Nations Programme for the Environment – UNEP. The international executive agency was the General Secretariat of the Organization of American States – OAS and the original national executor was the Water Resource Secretariat of the Ministry of the Environment – SRH / MMA, until May of 2001, when the responsibility was transferred to the National Water Agency – ANA. The Federal University of Viçosa (UFV), through its Agricultural Engineering Department, was responsible for the coordination of the Activity, whose objectives were quantifying the availability of water in the Basin, characterizing the use of water by agriculture and assessing irrigation efficiency. The fulfilling of these objectives will provide subsidies for the optimization of the use of the water resources and, consequently, augmentation of the availability. Thus, the work is subdivided into chapters corresponding to a description of the Basin’s general characteristics, to an analysis of its hydrologic regime and to the use of water by irrigation.
1. GENERAL CHARACTERISTICS OF THE SÃO FRANCISCO BASIN The São Francisco Basin (Figure 1) is located between the 7º and 21º S latitudes and the 35º and 47º40’ W longitudes, spreading over the States of Minas Gerais, Bahia, Goiás, Pernambuco, Sergipe and Alagoas, besides the federal District. From its origin, in the Sierra da Canastra, to its mouth in the Atlantic Ocean, the River travels around 2,700 km, draining a 639,219 km2 area, in which there are 503 Municipalities, with a 1999 population of 15,545,866 inhabitants (CODEVASF, 2002b). The Basin is traditionally divided into four sub regions: the Upper São Francisco (from its origin to the City of Pirapora); the Middle São Francisco (from Pirapora to the City of Remanso); the
i Middle-Lower São Francisco (from Remanso to Paulo Afonso) and the Lower São Francisco (from there to its mouth).
Figure 1. São Francisco Basin (from http://www.sfrancisco.bio.br/mapbacia.htm)
ii In the mouth of the River, the long term mean discharge is presented in the literature with values varying from 2,850 (ANA, 2002b) to 3,360 m3/s (ANA, 2002a; ANEEL, 2002a). The tributaries with permanent flows originate, predominantly, in the cerrados of Minas Gerais (Upper and Middle São Francisco) and in the Western part of Bahia, thanks to the higher precipitation depths in the Region and to the great permeability and thickness of the local soils. Around 85% of the water in the River is originated in the cerrados and 72% comes from the State of Minas Gerais. Water demands for the various uses in the basin are around 224 m³/s. From this total, 28 m³/s (12.5%) are for urban supply, 160 m³/s (71.4%) for irrigation, 7 m³/s (3.1%) for animal consumption and 29 m³/s (13%) for industrial purposes (ANA, 2002b). The São Francisco, with annual potential water storage of 64.4 billion m3 (2,042 m3/s), is responsible for 69% of the total surface reserves and 73% of the firm availability in Northeastern Brazil. The surface storage capacity in the Northeast is 85.1 billion, with 50.9 billion stored within the Basin, in the reservoirs of Sobradinho (34.1 billion), Itaparica (11.8 billion), Xingó (3.8 billion) and Moxotó (1.2 billion). Três Marias, outside of the Northeast, but within the São Francisco Basin, stores additional 19.3 billion m3 (CODEVASF, 2002b). Until the end of 2000, the Company for the Development of the São Francisco and Parnaíba Rivers (CODEVASF) had already built 270 dams with a total storage capacity of 1.4 billion m3. According to the Brazilian Hydroelectric Power Information System, of the Brazilian Hydropower Systems and Electrical Plants Planning Coordination Group, the São Francisco Basin has a potential power generation in the order of 26,346 MW. Until November of 1997, 9,290 MW were already installed and operating, what persists until now. At the time, plants with 1,000 MW capacity were under construction. The São Francisco Basin, with 64 million hectares, has 25.6 million hectares (40%) of agriculturable land. In the Upper and Middle São Francisco, where rainfalls are more abundant and regular, rainfed agriculture predominates. In the Middle-Lower, the activity is limited, as the area rests on the Semi-Arid Region. The downstream part of the Middle is also within the semi- Arid, being subject to the same restrictions (Vale do São Francisco, 2002c). Of the agriculturable land, 3 million hectares are irrigable, but only 300.000 hectares (10%) are presently being irrigated (Vale do São Francisco, 2002b). According to Lima and Miranda (2001), from 1970 to 1990, irrigated area in the São Francisco presented a 286% growth, which corresponds to 8,620 ha/year, while the economic development growth was 266%. Only in the 1980-1990 period, irrigated area in the Basin reached 61%. Governmental involvement in the São Francisco Basin is significant, being represented mostly by CODEVASF, whose basic mission is to promote regional development, through irrigated agriculture. The major part of the Basin presents ideal climatic conditions for irrigation, combining elevated temperatures and sunlight with relatively low humidity. Nevertheless, water deficit is high, given the small amount of precipitation and irregular distribution of rainfalls. The Region has a great diversity of climates, going from humid, in the Southern and Western parts, to semi-arid, in the Juazeiro/Petrolina area. Annual mean precipitation depths vary from 400 to 1,600 mm.
iii From 1970 to 2000, irrigated areas in the Semi-Arid underwent significant changes, particularly with respect to the used crops. Irrigation projects in the Basin, both public and private, still lack adequate planning and, even after their implementation, they have not been subject to a proper management. The water resources sustainability indexes estimated by studies under way area cause of concern, with respect to the availability of water for multiple uses. Some areas, such as Northern Minas Gerais, Rio Verde Grande Basin and the Salitre River Basin, in the State of Bahia, are already considered critical, regarding the demand/availability ratio. According to CODEVASF (2002c), in 1994, the multipurpose demands in the Basin were 9.1 billion cubic meters: 6.4 billion (70.3%) corresponding to ecologic demand (non-consumptive) and 2.7 billion (29.7%) to consumptive uses. Even though the São Francisco Basin has presented a significant growth in agricultural activities, the results were not immediate for the regional economy. That was due to a decentralized commercialization of the products, still with inadequate quality and standards, and to the lack of air transportation to allow the conveyance to the distribution and consumption centers. Today, regional centers such as Juazeiro-Petrolina, Pirapora, Janaúba-Jaíba, and Barreiras, have stood out both in the production and commercialization of their products, and the installation of agroindustries has resulted in added value to the products, in the own Region. Some of these centers are more noticeable in the Basin, due to their geographical location, existing infrastructure and also by their level of production. Chart 1 presents water demands in the São Francisco Basin and indicates that irrigation is responsible for 74.1% of the consumptive use. The present development of the São Francisco Basin is, in part, due to the implementation of public and private irrigation projects, which changed and continue to change the regional economy. This change, however, occurred in a relatively short period, for approximately 20 years, which was not enough to allow immediate learning and adoption of adequate irrigation management techniques, nor of preventive and corrective maintenance of the equipment.
Chart 1. Water demands in the São Francisco Basin, by type and use, in 1994.
Type of use Water demands in the Basin Annual demand (106 m3) % of total demand % of use Non-consumptive use 6.4 70.3 100.0 Ecological purposes 6.4 70.3 100.0 Consumptive use 2.7 29.7 100.0 Irrigation 2.0 22.0 74.1 Urban supply 0.3 3.3 11.1 Agroindustrial uses 0.1 1.1 3.7 Livestock raising 0.2 2.2 7.4 Industrial uses 0.1 1.1 3.7 Use in rural areas 0.0 0.0 0.0 Total 9.1 100.0 - [source: Áridas (2002)]
iv Inefficient and inadequate irrigation implies in waste of water and energy, finite resources scarcer by the day, what points to the importance of assessing the efficiency of practices adopted in the Basin.
2. EVALUATION OF THE HYDROLOGIC REGIME IN THE BASIN In the evaluation of the hydrologic regime in the São Francisco Basin, consisted data from 336 pluviometric stations and 283 fluviometric stations, belonging to the hydrometeorologic network of the Brazilian National Water Agency (ANA) and National Electrical Energy Agency (ANEEL), were analyzed. All information was obtained from the Superintendence of Studies and Hydrologic Information da ANEEL. The criteria used for selecting the stations included a 10-year minimum non-interrupted operating time . The 1950-1999 period was used as basis for the study. In this manner, 178 pluviometric and 77 fluviometric stations were effectively used for the investigation. The evaluation was carried out in the following stages: • Filling gaps and extending the series. • Estimates of mean precipitation depths in the contributing drainage area for each fluviometric station. • Estimates of the 7-day minimum flows. • Estimate of maximum annual flows. • Estimate of the discharge coefficient (ratio between volume of water flowing through the considered section and total precipitated volume). • Obtaining the flow-duration curve. • Estimates of the absolute and relative variations and the significance of the variation in the hydrologic variables during the considered period. Given the volume of estimates necessary for the investigation, an specific software was developed to help in the analysis. The software was divided into three modules: Flow, Precipitation and Flow versus Precipitation.
2.1 SPATIAL VARIABILITY OF THE MAIN HYDROLOGIC VARIABLES CONSIDERED Figure 2 shows a map of isohyets for mean annual precipitations in the 1950-1999 period. It is noticed that precipitation at headwaters reaches values higher than 1,700 mm, with decreasing values towards the River’s mouth, until the proximity of border of the Middle-Lower and the Lower São Francisco. From there on, there is an evident increase in precipitation depths. The minimal precipitation in the basin occurs in the Middle-Lower São Francisco, where annual means are lower than 450 mm. Mean annual precipitations vary from 1,000 to 1,750 mm in the Upper São Francisco, from 550 to 1,750 in the Middle, from 400 to 550 in the Middle-Lower and from 400 to 1,300 in the Lower.
v
Figure 2. Mean annual precipitation (isohyets) in the São Francisco Basin.
Figure 3 presents the distribution of the mean long-duration flows in River, emphasizing that flows in the main course are less than 1,000 m³/s in the Upper São Francisco, between 1,000 and 2,700 in the Middle and between 2,000 and 2,700 in the Middle-Lower and Lower stretches. The mean long-duration flows at all stations in the São Francisco tributaries are less than 1.000 m3/s. Chart 2 presents, for the 77 fluviometric stations under analysis, the mean precipitation depths and the long-duration mean specific discharges. Mean precipitation varies from 1,506 mm (Porto do Passarinho) to 847 mm (Boca da Caatinga). There is also great variation in long-duration mean specific discharges with values ranging from 28.19 l/s/km2, in Vargem Bonita, to 1.07 l/s/km2, in Boca da Caatinga. With respect to stations located at tributaries of the São Francisco, lower mean precipitations depths and specific discharges were verified in Sub-Basins closer to headwaters, compared to those closer to the mouth of the River. Sub-Basin 40 presents a mean precipitation of 1,386 mm and an specific discharge of 17.25 l/s/km2, compared to 1,040 mm and 5.52 l/s/km2, respectively, in Sub-Basin 46. The only exception to this rule is Sub-Basin 44.
vi
Figure 3. Distribution of long-duration discharges in the São Francisco Basin.
Chart 2. Drainage area, mean precipitation and mean long-duration specific discharge, for the 77 stations under analysis (1950-1999).
ANEEL Sub- Drainage area Mean Precipitation Mean long-duration specific Station code Basin (km2) (mm) discharge (l/s/km2) Station sub-basin Station sub-basin Vargem Bonita 40025000 299 1,420 28.19 Tapiraí 40060000 543 1,430 22,23 Carmo do Cajuru 40150000 2,402 1,387 15.67 Jaguaruna 40300000 1,545 1,367 12.85 Velho da Taipa 40330000 7,350 1,399 13.42 Estação Álvaro da Silveira 40400000 1,803 1,422 14.13 São Brás do Sacuí- 40 1,386 17.25 Montante 40549998 446 1,362 16.93 Entre Rios de Minas 40680000 469 1,367 18.53 Belo Vale 40710000 2,690 1,362 17.79 Alberto Flores 40740000 3,945 1,355 15.34 Ponte Nova do Paraopeba 40800001 5,680 1,357 14.65 Ponte da Taquara 40850000 8,720 1,358 14.40 Barra do Funchal 40930000 881 1,428 20.16
vii Iguatama * 40050000 4,846 1,415 22.61 Ponte do Chumbo* 40070000 9,255 1,365 18.86 40 1,388 18,63 Porto das Andorinhas* 40100000 13,087 1,384 16.37 Porto da Barra * 40102000 14,370 1,386 16.66 Major Porto 41050000 1,396 1,482 13.66 Porto do Passarinho 41075001 4,330 1,506 15.62 Ponte Raul Soares 41340000 4,780 1,347 16.06 Pirapama 41600000 7,838 1,319 13.12 41 1,345 14.00 Ponte do Licínio 41650000 10,980 1,292 11.89 Presidente Juscelino 41780000 3,912 1,333 18.47 Santo Hipólito 41818000 16,528 1,277 12.21 Várzea da Palma 41990000 25,940 1,206 10.93 Pirapora-Barreiro * 41135000 41 61,980 1,349 1,349 13.68 13.68 Porto Aliança 42090000 4,374 1,034 Santa Rosa 42395000 12,880 1,336 42 1,236 Porto da Extrema 42690001 29,060 1,279 Porto Alegre 42980000 40,300 1,293 Montante Barra do Jequitaí * 42030000 42 90,990 1,305 1,288 12.03 11.64 Cachoeira da Manteiga * 42210000 107,250 1,271 11.24 Arinos 43430000 11,710 1,295 12.26 Vila Urucuia 43670000 18,600 1,266 11.33 Fazenda Conceição 43675000 43 2,200 1,162 1,236 14.40 11.83 Santo Inácio 43880000 23,765 1,227 10.77 Barra do Escuro 43980000 24,658 1,228 10.37 São Romão * 43200000 43 154,100 1,271 1,271 10.62 10.62 Usina do Pandeiros 44250000 3,812 1,168 6.54 44 1,008 3.81 Boca da Caatinga 44950000 30,474 847 1.07 São Francisco * 44200000 182,537 1,262 11.04 Pedras de Maria da Cruz * 44290002 44 191,063 1,250 1,250 10.71 10.54 Manga * 44500000 202,400 1,237 9.88 São Gonçalo 45131000 6,186 1,229 11.20 Fazenda Porto Alegre 45170000 5,730 1,151 10.94 Lagoa das Pedras 45210000 12,120 1,181 11.00 Capitânea 45220000 2,196 1,140 6.12 Juvenília 45260000 15,600 1,148 9.54 Correntina 45590000 45 4,075 1,008 1,121 7.91 9.17 Mocambo 45740000 8,130 958 5.37 Arrojado 45770000 5,278 1,110 10.90 Gatos 45840000 6,867 1,182 11.67 Colônia do Formoso 45880000 8,695 1,182 Santa Maria da Vitória 45910000 29,570 1,044 7.04 Carinhanha * 45298000 251,209 1,179 8.87 45 1,165 8.29 Bom Jesus da Lapa * 45480000 273,750 1,150 7.70 Derocal 46455000 6,231 1,103 7.83 Fazenda Coqueiro 46490000 4,300 1,055 1.21 Fazenda Redenção 46543000 5,400 1,103 8.89 Barreiras 46550000 18,560 956 5.70 Nova Vida 46590000 7,155 1,038 6.60 São Sebastião 46610000 46 32,586 1,081 1,040 5.51 5.52 Taguá 46650000 35,564 1,081 5.02 Fazenda Macambira 46675000 39,256 1,065 4.47 Formosa do Rio Preto 46790000 14,210 952 6.52 Ibipetuba 46830000 18,200 983 4.99 Boqueirão 46902000 68,540 1,018 3.97 Paratinga * 46105000 318,028 1,123 7.29 Ibotirama * 46150000 325,200 1,115 7.39 46 1,098 6.97 Morpará * 46360000 348,074 1,086 7.12 Barra * 46998000 433,280 1,068 6.09 Pilão Arcado * 47302000 47 443,100 1,044 1,044 5.90 5.90 Juazeiro * 48020000 510,800 984 4.94 Sta Maria da Boa Vista * 48290000 48 530,000 966 964 4.80 4.74 Ibó * 48590000 568,600 943 4.49 Pão de Açúcar * 49370000 608,900 907 4.34 49 905 4.28 Traipú * 49660000 622,600 903 4.22 (*) Stations in the main course of the São Francisco River
viii To allow an easier interpretation of the hydrometeorological data, the classification of basins proposed by ANEEL was adopted. The São Francisco Basin (Basin 4) was divided into 10 Sub- Basins (numbers 40 to 49). A look in the above chart confirms a reduction in flows in spite of larger contribution areas, for the stations closer the mouth of the River. Iguatama, the first station in the São Francisco, with a 4,846 km2 drainage área, presents a specific discharge of 22.61 l/s/km2, the greatest among those located in the main course, while the last station, Traipú, with a 622,600 km2 drainage area, presents the lowest values (4.22 l/s/km2). Figure 4 displays a map with the distribution of mean values of maximum discharges, for the 1950-1999 period. It is noticeable that maximum flows are inferior to 4,000 m³/s in the main course of the Upper São Francisco, between 4,000 and 7,800 m³/s in the Middle and Middle- Lower sectors and between 7,000 and 7,800 m³/s in the Lower reach. The reduction in maximum discharges for the stations in Juazeiro, Santa Maria da Boa Vista and Ibó, compared to stations located upstream from them, is caused by the river regulation imposed by Sobradinho Reservoir, with a 34.1 billion m³ storage capacity. The distribution of the mean 7-day low flows (Figure 5) indicates that the minimum discharges, in general, are increasing along the River. The mean values recorded in the main course are inferior to 500 m³/s in the Upper São Francisco, between 500 and 1,700 m³/s in the Middle, and between 1,000 and 1,700 m³/s in the Middle-Lower and Lower reaches. Analysis of the distribution of discharges associated with a 95% of permanence shows a behavior similar to the verified for the 7-day low flows. The greatest runoff coefficients (ratio between drained and precipitated volumes) were verified in pluviometric stations with smaller drainage areas and higher precipitation depths. The runoff coefficients varied from 0.3 to 0.5 in the stations located in the Upper São Francisco, from 0.1 to 0.3 in the Middle section and from 0.1 to 0.2 in the Middle-Lower and Lower stretches, emphasizing the importance of headwaters areas to the perpetuity of the São Francisco.
2.2. TEMPORAL VARIABILITY OF THE MAIN HYDROLOGIC VARIABLES Figures 6 and 7 present maps of precipitation and mean annual flows, respectively, in the São Francisco Basin, in the 1950-1999 period. In the Upper São Francisco, an increase in mean annual precipitation with time is noticed, in the drainage areas corresponding to the studied fluviometric stations. This increase in precipitation implies in an augmentation of mean annual discharges. The maximum flow also presents a growth in the period of analysis, except for the Pirapora-Barreiro station, the only one downstream from the Três Marias Power Plant, in the Upper São Francisco, therefore under the regulating impact resulting from the construction of the dam. The minima7-day low flows increased with time for all the stations in the main course of the Upper São Francisco (Sub-Basins 40 and 41), a trend also verified for the discharges associated with a 95% of permanence. This behavior is consequence of the augmentation of the mean annual precipitation, which also implied in a greater runoff coefficient.
ix x
. Figure 4. Distribution of maxima discharges Figure 5. Distribution of minima 7-day low flows.
x (a) (b)
N
W E S SB 48 S# # IBO S A N T A M AR I A DA B O A V I S T A SB 49 #
S# $ S# $ $ # $ JUAZ EI R O ( P C D ) $ P A O D E AC UC A R #
# S# S# S# TRAIPU # P I L A O A RC ADO
SB 47 S# S# I B I P ET UBA # S# BARRA # F O R M O S A DO R I O # PR ETO (PCD) S# B O Q UE I RAO # F A Z E N DA M AC A M B I RA # MORPARA TA G U A # NOVA V ID A-M ONT ANTE S# # S# S#
# # S# SAO SE BA STIAO IBO TIRAMA FAZEND A R EDENCAO # # S S# # # S# B A R RE I RA S S# # # S# S# D E RO CA L F AZ ENDA CO Q U E I RO # P A R ATI NG A SB 46 MOC AMB O S# CORR E NTI N A SA NTA M A R I A D A B OM J E S U S DA L APA S# VITORIA # # # S # 80 0 80 160 240 Km # ARRO JADO # S#
# S# S# G A T OS #S# S# C O L O N I A D O F O R M O S O F A Z E N DA P O R TO L A G OA D A S P EDRA S AL EG RE SB 45 S# S# J UV E N I L I A (P C D ) # # # SAO G ONCA L O # # CARINHAN HA S# # S# S# Legenda: CAP ITANE A xi BOC A D A CAA TIN GA S# # # M A N G A S# S# Hid r o gr afi a SB 44 SB 43 S# SB Sub-bacias segundo classificação da ANEEL USINA DO PAND EIROS # PEDRA S D E M ARIA DA C RU Z # # SAN TO INACIO Est açõ es fl u vi o mé tr i ca s est udadas S# S# ARINO S # # $ S# S# S A O F R ANC I S C O Usi n as hid relé tric a s BARRA DO ES CURO VILA U RUC UIA # # S# S # # FAZENDA C ONCEICA O # S# S# # S A O RO M A O ( PCD) Es c a la de co res CACHO EIRA DA MANTEIGA # S# S# # S# MON TANTE B A RRA D O JEQ UIT AI Positiva Negativa POR TO DA EX TREMA PORTO ALEGR E # # S# P O RTO A L I A NC A SAN TA RO SA S# # # 0 - 9,9 0 - 9,9
# S# S#
SB 42 # 10 - 19,9 10 - 19,9 PI RA P O RA -B A RR E I R O S# VAR Z EA D A P AL M A 20 - 2 9,9 20 - 29,9 SAN TO HIPOL ITO SB 41 P O R TO DO PAS S A R I NH O $ S# # 30 - 39,9 30 - 39,9 # # S S# PONTE DO LICINIO PRES I D ENTE J US CEL I N O # 4400--4499,,99 40 - 49,9 # S# M A J O R PO RT O # S# PO RTO DAS
AND ORINHAS POR TO DA PIRAPA MA > 50 > 50 # BARR A S# S# VEL HO DA # Precipitação (mm) S# # PONTE DA TA QUARA S# T A I P A # BAR RA DO FUNC HAL # P O NTE DO CH UM B O S# PO NTE RA UL S O A R E S # S# S#
# # S# # S# # PON TE NO VA DO PA RA OPEBA
S# # # S TAPIRA I EST ACAO ALV ARO S# JAG UA RUNA # D A S I L VE I R A AL BE R TO F L O RE S S# S# # # # BEL O VALE # S# VAR GE M BON ITA S# #S# C A R M O D O CAJ URU IGUATAMA SB 40 S# # SAO BR AS DO SUAC UI-MO NTANTE # S# ENT RE RIO S DE MIN AS
Figure 6. Variation of absolute (a) and relative (b) mean annual precipitation, in the São Francisco Basin (1950-1999)
xi (a) (b) xii
Figure 7. Variation of the absolute (a) and relative (b) mean annual discharges in the São Francisco River and in its tributaries, in the 1950-1999 period.
xii In Pirapora-Barreiro (border of Sub-Basins 41 and 42), the increase in the minima 7-day low flows with a 95% permanence was more significant than in other areas, given the regulating effect of the construction of the Três Marias dam. In the Middle São Francisco (Sub-Basins 42 to 46), there is a trend for lowering the mean annual precipitation with time, in the drainage areas of the fluviometric stations studied in the Basin. All these variations are of little significance, every one of them inferior to 30%. However, discharges in the main course of the Middle São Francisco have a tendency to behave in the opposite way, as both the mean annual discharge, maxima and minima flows, as well as the flow with 95% permanence, have increased with time, which is representative of the great complexity of the hydrologic processes in the Basin. A possible explanation for such behavior is the verified increment in precipitation in the January, a month already characterized as one with high incidence of rainfalls. Obviously, the additional precipitation is responsible for the augmented maxima flows. The growth of the minimum discharge and of the discharge associated with the 95% permanence, however, is probably due to the regulating effect of the reservoirs built in the Upper São Francisco and tributaries, as is the case of the Três Marias. In the Middle-Lower (Sub-Basins 46 to 48), there was an evident trend of increase in mean annual precipitation, in the areas under analysis. However, the mean and maxima discharges, as well as runoff coefficient, presented reduction with time, while the minima 7-day flows and the flow associated with 95% permanence increased with time. The variation trends of flows in the Middle-Lower and Lower reaches may be explained by the construction of several hydro-power plants (Sobradinho, Itaparica/Luiz Gonzaga, Moxotó, Paulo Afonso and Xingó). The tendency for reduction in mean flows and in runoff coefficients are also directly related to hike in evaporation losses, resulting from the construction of reservoirs. The increase in diverted flows from the São Francisco, to meet the expressive growth of production activities verified in the Region, has also contributed to the condition. In the stations of Santa Maria da Boa Vista (482900000) and Ibó (48590000), located immediately downstream from the Sobradinho Power plant, the minima 7-day flows and the flows with 95% permanence was distinct from that of other stations in the same reach. This is due to the fact that only the period posterior the construction of the dam was used in the analysis of those stations (1979 a 1999). Figure 8 presents, for the station of Boca da Caatinga (44950000), the variation in mean precipitation, mean flows, maxima and minima 7-day flows, for the 1970 to 1994 period. The station, located in the Verde Grande River (Middle São Francisco), has a 30,474 km² drainage area, with a mean precipitation of 847 mm and mean long-duration specific discharge of 1.07 l/s/km². Analysis of the outcomes indicates a little reduction in precipitation, with time, which contributes to the little decrease verified in the mean annual flows and runoff coefficients.
xiii 1600
Mean Prec. = -1,3195 (year) + 3462,4 /s) 3 1400 120 1200 Mean discharhe = -0,1074 (year) + 245,48 Mean precip (mm) 1000 100 Mean discharge (m
800 80
600 60 400
200 40
0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 20 Time (year) Mean annual precip Adjusted equation 0 (a) 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Time (year) Mean annual discharge Adjusted equation
xiv (c)
900 /s)
3 8
800 Maximum discharge = -0,1232 (year) + 246,77 Maximum discharge = 4,0068 (year) - 7701,3 7
700 6 600
Maximum discharge (m 5 /s) 3 500 4 400 3 300
2 Maximum discharge (m 200
100 1
0 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Time (year) Time (year) Maximum abbual discharge Adjusted equation 7-day maximum discharfge
Figure 8. Mean annual precipitations (a), mean annual flows (b), maxima annual flows (c) and mínima 7-day low-flows (d), in the station at Boca da Caatinga (1970-74).
xiv The maxima annual flows present an increment of 4.01 m3/s/year, which results from the increases verified in the mean precipitation depths in January. As noticed in the analysis of the outcomes, the significance associated with variations in mean precipitations, mean flows and maxima flows, with time, were inferior to 53%, which confirms their little significance. The same cannot be stated with respect to minimum 7-day flow, which registered a decrease of 0.12 m3/s/year (∆Rel = 72.7%; Sign = 95.7%), and to flows associated with a 75% or greater permanence, for which we have ∆Rel greater than 50% and Sign greater than 90%. The high relative variance and high significance obtained for the minima 7-day low flows and flows associated with longer permanencies point to a clear impact in the discharge of the Verde Grande River, in the dry months. Other things worth mentioning, for Boca da Caatinga, are the fact that this station presents the lowest mean annual precipitation (847 mm) and the smallest runoff coefficient estimated for the period of analysis. Figure 9 shows the variation in mean precipitation, mean flow, maximum flow and 7-day flows, for Juazeiro (48020000), for 1950 through 1999. The periods of 1950-1973 and 1979-1999, corresponding to periods before and after the filling of the Sobradinho Reservoir, are evaluated individually. The station in Juazeiro is located at the limit of Sub-Basins 47 and 48, being immediately downstream from the Reservoir. This station registered three successive years (1979-81) with annual precipitations above the usual, which was repeated in the years of 1983-85. After 1994, precipitations were bellow average, and high rates of reduction were noticed, from 1979 to 1999. The behavior of the precipitation was decisive also in terms of flows, which presented a similar conduct. Chart 3 presents the mean annual and monthly flows for the stations of Ibotirama (46150000) and Juazeiro (48020000), for the 1950-1973 and 1979-1999 periods. For Juazeiro, the analysis was made for both the historic data and the series obtained by filling gaps with data from Bom Jesus da Lapa (45480000) and Ibotirama. As it becomes evident in Chart 3, there was a clear difference between the mean annual flows obtained for Juazeiro, using historic data for 1979-1999 (2,584 m³/s) and values estimated using series filled with data from the stations in Bom Jesus da Lapa (2,916 m³/s) and in Ibotirama (2,950 m³/s). Both alternatives are listed in the Chart. These values correspond to a reduction of 350 m³/s in the actual discharge, compared to estimated values, indicating a change in the regime of flow in the São Francisco, downstream from Juazeiro, after 1979. The actual mean flow for Ibotirama, with a 325,200 km² drainage area, of 2,644 m3/s, is superior to the 2,584 m3/s for Juazeiro, whose drainage area is 510,800 km2. This fact emphasizes the impact of the construction of Sobradinho and of the activities in this part of the Basin, standing out the boom of irrigation, on the regime of flows in the Basin. Even with the increase of 185,600 km² (57.1 %) in the drainage area, it is noticed a reduction equivalent to 60m3/s in the mean discharge.
xv 5000 1600 Mean Precipitation (mm) 4500 1400 4000
1200 3500 /s) 3
1000 3000
800 2500 2000 600 Mean discharge (m 1500 400 1000 200 Mean prec. = 1,1626 (Ano) - 1320,4 Mean prec. = -10,413 (Ano) + 21713 500 Mean discharge = 1,6470 (year) - 702,9206 Mean discharge = -105,0465 (year) + 211526,0506 0 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Time (year) Time (year) Mean annual precip (1950-1973) Mean annual precip (1979-1999) Mean annual discharge (1950-1973) Mean annual discharge (1979-1999) Adjusted equation: Adjusted equation: Adjusted equation Equação ajustada
xvi /s) 3
16000 Maximum discharge = -14,3052 (year) + 34160,8506 Maximum discharge = -312,3104 (year) + 626846,8411 2500 14000 Vazão mínimaVazão (m 12000
/s) 2000
3 10000
8000 1500
6000 1000 Maximum discharge (m 4000
2000 500 Maximum discharge = 18,9858 (year) - 36238,1419 Minimum discharge = -31,6826 (year) + 64643,5884 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 0 Time (year) 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Maximum annual discharge (1950-1973) Maximum annual discharge (1979-1999) Time (year) Adjusted equation Adjusted equation 7-day minimum discharge (1950-1973) 7-day minimum discharge (1979-1999) Adjusted equation
Figure 9. Mean annual precipitations (a), mean annual flows (b), maxima annual flows (c) and minima 7-day low-flows (d), in the station at Juazeiro (1950-73 and 1979-99).
xvi Chart 3. Mean and monthly flows (m3/s) in the stations of Bom Jesus da Lapa, Ibotirama and Juazeiro (1950-1973 and 1979-1999).
(1 Station Period Annual ) Jan Feb Mar Abr Mai Jun Jul Ago Set Out Nov Dez 194 357 358 328 269 137 104 164 299 Bom Jesus da 1950 - 1973 1 6 7 7 1 8 1 883 747 680 877 3 4 Lapa (BJL) 236 427 429 371 279 176 144 130 119 115 129 199 321 1979 - 1999 2 9 5 6 0 5 2 3 4 8 0 5 9 223 376 390 371 308 165 130 116 102 121 190 319 1950 - 1973 2 9 4 3 6 8 9 3 0 935 7 2 7 Ibotirama (Ibo) 264 452 482 433 315 203 167 150 138 134 149 217 339 1979 - 1999 4 4 3 9 1 4 1 9 9 9 3 5 1 253 405 443 416 385 222 159 138 123 110 122 187 333 Juazeiro: 1950 - 1973 2 4 7 6 9 2 9 9 9 1 4 7 4 historic data 258 321 370 385 323 234 201 195 198 204 203 215 253 1979 - 1999 4 1 0 8 7 9 4 3 5 2 4 5 5 Juazeiro: 291 453 488 439 396 295 210 183 165 152 154 217 352 1979 - 1999 data from BJL 6 5 6 7 8 2 2 5 6 9 3 5 9 Juazeiro: 295 441 567 501 396 258 192 168 154 144 149 217 364 1979 - 1999 data from Ibo 0 7 8 9 9 6 9 6 0 1 2 0 3 - - - ∆ [filled and 12, 41, 32, 14, 22, 25, 16, 25, 24, 39, ∆ Juazeiro: hist.] (%) 8 2 1 0 6 7 4,4 -6,1 6 1 1 0,9 2 (BJL / Hist) 132 118 - - - - 1979 a 1999 333 539 731 603 88 20 994 4 6 119 329 513 490 - - - - ∆ [filled and 14, 37, 53, 30, 22, 10, 13, 22, 29, 26, 43, ∆ Juazeiro: hist.] (%) 2 6 4 1 6 1 -4,2 7 4 4 6 0,7 7 (Ibo / Hist) 120 197 116 - - - - 110 1979 a 1999 367 732 237 -84 15 6 7 1 267 445 600 541 7 (1) Value corresponding to the ponderated average of monthly flows, considering the number of days in month.
Analysis of the changes in mean monthly discharges permits the observation of the regulating effect of the reservoir, as in the months of December through February the difference between actual flows and those estimated considering the behavioral trends of historic flows prior to 1973 is greater than 990 m³/s. This fact shows the impact of the reservoir in flood control, which resulted in reduction of the maxima flows in downstream reaches. In the dry season, the mean monthly discharges estimated with data from other stations are inferior to those verified in the River. Discharges estimated based on the expansion of shorter series were lower than the observed, in the months of June through October. Those differences reached 600 m3/s, with the minimum monthly mean in the historic series equal to 1,953 m3/s, in July. The lowest values in the series with filled data were 1,441 m3/s, using data from Ibotirama, and 1,529 m3/s, with data from Bom Jesus da Lapa, in September. This shows the shift of the month of occurrence of the lowest flow downstream from Juazeiro, which went from September, prior to 1979, to July, after 1979. Figure 10 presents a schematic summary of the mean discharges in the São Francisco River and in its tributaries, for the 1950-1999 period.
xvii
a v ti s s R R E a i d i o a o í n r d C O P a á o o u o r i r r a e i e q r R e # r u # d t a e n o t G o I n i a R t o J io i i R i # n # e o R a R d # I n # io # R # # d io R o a # t R A i rr # e á i o # r o ja d # P R # R o R A R i o o i b # i i i o C o o a R o # R R x C G 17,76 e U i á io o t r a F r # é R # o a 67,61 u P r