Author Topic: Amazon underground river survey report (Rio Hamza) - Pimentel and Hamza  (Read 17023 times)


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Amazon underground river survey report (Rio Hamza)

Indications of an Underground "River" beneath the Amazon River: Infernces from Results of Geothermal Studies
Elizabeth Tavares Pimentel - UFAM/ON
Supervisor: Dr Valiya Mannathal Hamaza-ON

Indications of an Underground "River" beneath the Amazon River: Infernces from Results of Geothermal Studies (pdf)

Fluvial systems of the Amazon basins constitute one of the largest drainage systems on the surface of the Earth. The Characteristics of this surface discharge system have been the object of a large number of investigations over the last several decades (Jaccon and Cudo 1987; Guimaraes et al 1983; Molinier et al 1994)

Nevertheless relatively few investigations have been carried out in understanding the characteristics of recharge and discharge of groundwater and conditions of subsurface flow in this region.

Most of the studies of groundwater hydrology in the Amazon region has been carried out as part of investigations of subsurface flow systems on local scales, there being very few evaluations on regional scales.

In this context the main objective of the present work is to examine in the characteristics of geothermal data acquired in deep boreholes and wells and its use for determining regional scale subsurface fluid flows of groundwater in the Amazon region.

The principle of geothermal method for study of grounwater flows can be understood by considering the role of advection heat transfer on the conductive regime of subsurface layers.

Studies on the use of geothermal methods for obtaining information on groundwater flows were carried out by Cartwright 1970, Mansure and Reiter 1979, Hamza 1982, Hamza et al 1986, Yamabe and Hamza 1996 and Assumpcao et al 2010

Conduction - Advection Equation
Under steady state conditions the equation for simultaneous heat transfer by conduction and advection in a porous and permeable medium of homogeneous thermal properties is (Stallman 1963)

... equations and explanation of them (view pdf to see them all) ...

Modified Scheme for temperature distribution in the presence of groundwater flow in sedimentary basins:
- Curvatures in Temperature profiles are mainly due to advection
- Groundwater flows extend all the way to the basement
- Lower limit is set on the basis of data on porosities of main rock types

The results obtained reveal that concave shaped curvatures in temperature distributions in the Amazon Basins are typical of regional scale down flow of groundwater.

Such grouping was done in view of the indications that flow systems in the upper parts of sedimentary basins have velocities different from those at lower levels.

Characteristics of subsurface flows in the Amazon basins
Regional hydraulic gradient favours lateral flow from west to east i.e. from the foot hills Andean mountains to the Atlantic ocean
Porosity and permeability are large in the upper rock formations relative to the lower ones

The upper parts of the geological formations in Amazon basins are characterized by down flow of groundwater
The lower parts of geological formations in Amazon basins are characterized by both down and lateral (in the direction of west to east) flows of groundwater

Comparison of Flow Systems in the Amazon Basins

Analysis of the relations between dimensionless values of VHT and depth in oil wells has allowed estimates of the vertical recharge velocitires for groundwater flows in five distinct sedimentary basins of the Amazon region.

At shallow depths of less than 2000m the velocities are systematically high compared to those for deeper depth levels

Relatively high velocities of 3.4x10-9 m/s are observed in the Amazonas and Barreirinhas basins. The lowest value of 2.4x10-9 m/s is found for the Marajo basin. Intermediate values of velocitires are found for Acre and Solimoes basins.
The observed vertical recharge velocities are indicative of extensive subsurface lateral flow system in the direction of west to east in the Amazon region

(Schemetic Representation of the subsurface Flow system)

The overall subsurface lateral discharge rate estimated for the Amazon region is 3900 m3/s

For comparison purposes we note that this value is much higher than the surface discharge (2850 m3/s) of the Sao Francisco river system in the eastern parts of Brazil

We conclude that the impacts of of such lateral flow patterns must be included in assessment of overall hydrological systems for the Amazon region