A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone

Transcription

1 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Paulo Cesar Colonna Rosman Area of Coastal & Oceanographic Engineering Depart. Water Resources & Environment Escola Politécnica & COPPE/PEnO UFRJ Places and distances via Google Earth Recommended and ongoing responses Suspended sediments plume passing along the estuary Has the plume reached Abrolhos coral reefs?

2 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Samarco dams Places and Distances ~ 670 km from the Samarco dams to the sea ~ 80 km Gualaxo do Norte river ~ 30 km Carmo river ~ 560 km Rio Doce 4 reservoirs in the Rio Doce ~ 215 km from the Rio Doce mouth to Abrolhos

3 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Before and After: Dams and Bento Rodrigues District Fundão dam collapsed in 2015.Nov.05 The mud flow from the collapsed dam invaded the Santarém reservoir, and overtopped its dam (no collapse). Estimated overtoping volume = 35 million m³ Area covered by the mud flow before reaching the Gualaxo do Norte river 3.2 million m². ~ 10% of the thicker mud deposited Recommended zone for Bento Rodrigues Memorial Park with reforestation and landscaping

4 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Before and After: Gualaxo do Norte river (80 km) Destruction of riparian forests and deposits of mud in floodplains and marginal areas Recommended soil correction and reforestation of riparian forests along 2 80 km the Gualaxo do Norte river Impacted area in Gualaxo do Norte river ~ 120 m 80 km 9.5 million m². Mud deposits of ~20% of the original sediment volume

5 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Before and After: Gualaxo do Norte Carmo river Carmo river Gualaxo do Norte river Destruction of riparian forests and deposits of mud in floodplains and marginal areas Impacted area in Carmo river ~120 m 34 km 4 million m². Deposits of ~10% of the heavier mud Carmo river Recommended soil correction and reforestation of riparian forests along 2 34 km along the Carmo river

6 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Before and After: Rio Doce = Carmo + Piranga rivers Rio Doce Rio Doce has a wider section and suffered no relevant damage in riparian forests, because the passing muddy wave was more fluid, came with a ~40% reduction in sediment volume, and had already been quite dispersed. There was significant deposition of sediments in the reservoirs, especially in the first one, Risoleta Neves (ex-candonga). The biggest reservoir, about of 400 km downstream, is Aimorés

7 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Concentrations of Total Suspended Sediment (SST) will remain above normal in the Rio Doce, while: 1. Stocks of fine sediments deposited along the banks of Gualaxo do Norte and Carmo rivers remain available for erosion and keep being washed by rain into the rivers. Therefore, restoration of riparian forests must be done as soon as possible, to lessen availability of erodible sediments. 2. Stocks of accumulated mud in the bottom of the reservoirs of hydroelectric plants keep being flushed downstream during floods. It is recommended to evaluate the convenience of operating the gates in order to allow for scheduled sediment flushes, alleviating need for dredging. Such flushes could transport in a diluted form the deposited sediments, with controllable environmental risks. Dredging of fluid mud is challenging, has low efficiency, and disposal of the dredged material is problematic. Both the option of using large geotextile bags, to filter and retain the sediments, or the option of constructing marginal levees involve environmental challenges and high costs.

8 A hydro-sedimentological view of the Samarco disaster, focusing in the Rio Doce estuary and adjacent coastal zone Recommendations (Dec/2015): Restore the soil as soon as possible to create a Memorial Park where Bento Rodrigues existed. Reforestation with fertilization and soil correction, landscaping and maintenance of Memorial Monuments (Churches, ruins etc.), to retain sediment deposits, mitigating erosion by rain. The Memorial Park would represent an honorable and respectful memory of the victims of the tragedy. Restore as soon as possible the riparian zones of the rivers Gualaxo do Norte and Carmo. Reforestation with fertilization and soil correction designed to retain sediment deposits, mitigating erosion by rain. (Riparian zones of the Rio Doce were mostly unaffected.) Operate the reservoirs in order to provide gradual flushing of the fluid mud deposits, during rainy months.

9 Hydro-sedimentological aspects in the Estuarine Region of Rio Doce and adjacent Coastal Zone Technical team: Prof. Paulo Cesar Colonna Rosman D.Sc. Ludmila Assunção Pinheiro M.Sc. Rodrigo dos Santos Peixoto M.Sc. Patricia Auler Rosman Modeling done with SisBaHiA

10 SST (mg/l) Discharge Vazão (m 3 /s) Basic data of Rio Doce: River Discharge and Total Suspended Sediment (SST) Concentration Vazão - Estação Colatina Rio Doce discharge at Colatina, ES (~100 km upstream of the mouth) /11/ /12/ /01/ /02/ /03/2016 Date Tempo (dd/mm/yy) Sólidos Suspensos Totais - Linhares Total Suspended Sediments (SST) at Linhares, ES (~40 km upstream of the mouth) /11/ /12/ /01/ /02/ /03/2016 Date Tempo (dd/mm/yy) Data provided by Vale S.A. Date (dd/mm/yy) Granulometry

11 Tide Nível Elevation (m) (m) Basic data of Rio Doce: Winds and Tides Elevação da Maré Tides in the coastal zone near Rio Doce mouth /11/ /12/ /01/ /02/ /03/ m = IBGE Imbituba Datum Date (dd/mm/yy) Tempo

12 Digital Terrain Modeling

13 - 13 Hydrodynamic Modeling

14 SST (mg/l) Vazão (m 3 /s) LRF To assess these values consider: Transparent coastal waters: SST <10 mg/l. Waters in estuaries and bays: SST< 100 mg/l. Rivers with muddy waters: SST > 500 mg/l. Madeira river in the dry season: SST ~ 500 mg/l Madeira river in the flood season: SST > 3000 mg/l. Mouth of the Amazon river in the flood season SST ~ 2000 mg/l. Results showing passage of peak load of sediments arriving at the mouth in November /11/ /12/ /01/ /02/ /03/ Vazão - Estação Colatina Tempo Sólidos Suspensos Totais - Linhares 0 20/11/ /12/ /01/ /02/ /03/2016 Tempo

15 SST (mg/l) Vazão (m 3 /s) Results showing flood wave passage in the mouth: January 2016 To assess these values consider: Transparent coastal waters: SST <10 mg/l. Waters in estuaries and bays: SST< 100 mg/l. Rivers with muddy waters: SST > 500 mg/l. Madeira river in the dry season: SST ~ 500 mg/l Madeira river in the flood season: SST > 3000 mg/l. Mouth of the Amazon river in the flood season SST ~ 2000 mg/l. Vazão - Estação Colatina /11/ /12/ /01/ /02/ /03/2016 Tempo Sólidos Suspensos Totais - Linhares /11/ /12/ /01/ /02/ /03/2016 Tempo

16 Persistence of SST above 20, 50 and 100 mg/l between 20/11/2015 and 20/03/

17 Velocidade (m/s) Current Velocity (m/s) Maximum Northward Drift (km) Maximum sediment plume drift northward of the Rio Doce mouth Total Suspended Sediments (SST) and Maximum Northward Drift from the mouth Current Componente velocity component longitudinal parallel da corrente to the coastline de deriva induced induzida by pelos prevailing ventos winds N S /11/ /01/ /03/ /05/ /07/ /09/2016 Tempo Date (dd/mm/yy) 20 km northward of the mouth SST is ~20% of value in Rio Doce 40 km northward of the mouth SST is < 5% of value in Rio Doce