Each year the
Amazon transports suspended sediment to the delta plain. On average, the
sediment is composed of 1240Mt from Andean erosion and 3200Mt from flood
reworked plain sediments (“Channel floodplain geomorphology along the
The combined exchanges of sediment transport define a "sediment budget.” Such budgets estimate that an average of 2070Mt of sediment is exchanged per year. This sediment can be broken up into four groups: 1) Sediment entering the channel from bank erosion ~1570Mt/yr, 2) Sediment transferred from channel transport to bars ~ 380Mt/yr, 3) Channelized flow in flood plains ~ 460 Mt/yr, and 4) Diffuse overbank flow in the flood plain ~ 1230Mt/yr. In total, "deposition on bars and flood plain exceeded bank erosion by ~ 500 Mt/yr over a 10-16 yr period,” meaning there is a net accumulation of sediment both on the valley floor and in the delta plain each year.
this accumulation of sediment over time can be important to understanding where
pollutants such as mercury flow, and thus where the effects of such pollutants
should be studied. Understanding the
flow of nutrients provided by the regular deposition of sediment also helps to
understand how a change upstream in sediment collection may effect the
ecosystems surrounding the river. (“Exchanges of sediment between the flood
plain and channel of the Amazon River in Brazil” by Thomas Dunne, Leal A. K.
Mertes, Robert H. Meade, Jefferey E. Richey, Bruce R. Fursberg. From Geological Society of
both positive and negative effects on the upstream and downstream environments
due to the modification of the natural flow conditions. These effects include
higher temperatures, with little to no variation in temperature throughout the
course of a year; increased forest flooding, critical situation in reservoir
filling (from the sediment dropped when the water slows in the reservoir),
decreased residence time, increased eutrophication, increased gas formation,
corrosion of equipment and a decline in the water quality downstream. One possible solution that would negate these
negative effects is hydraulic equipment to reaerate reservoirs ("Water
Quality Simulation in Reservoirs in the
A NASA project called the "Global Rainforest Mapping project (GRFM) by an orbiting spacecraft using radar imaging, (Japanese JERS-1 Synthetic Aperture Radar (SAR))” is capable of monitoring sediment flows. The first SAR mapping of the Amazon (during low flood season) took 62 days. Another was done during high flood season. The advantage of SAR technology is its ability to be used at night and to see through clouds. This is particularly important as some areas of the rainforest are under perpetual cloud cover. This data may be useful in trying to model the carbon cycle and climate change. In addition, it can be used as a baseline with which to compare future data collections (http://southport.jpl.nasa.gov/amazon/imagebrowser/jamms.html).
Optical Backscatter (OBS)
This method uses photodiodes positioned around an emitter to measure the light reflected by a given sample. The method requires an empirical calibration to convert the measured backscatter to a concentration. Measurement sample volume "is on the order of several cubic centimeters," meaning it can best measure 200-400μm particles, and concentrations of up to 100g/L. These devices are readily available and relatively inexpensive. However, they require manpower to run the tests. There are many slight variations to this method.
This method takes advantage of the fact that sediment reflects a certain amount of sound depending on its concentration and particle size and the frequency of the sound. Short bursts of high frequency are emitted from a transducer. Using multiple frequencies, it is possible to determine both the particle sizes and concentrations. This technique can also be used to measure a vertical profile of sediment concentrations for depths of 1-2m. This acoustic technology is still under development.
sediment concentrations are measured using the amount of radiation reflected
from a body of water and the properties of that water. This can be
measured using a handheld, airborne, or satellite based spectrometers. One
major advantage of satellite-based spectrometers is the ability to measure a
much larger area. Because of the sheer size
"A charge-coupled device records the sediment/water mixture in-situ." Sediment can be analyzed for size as well as the concentration of suspended sediment particles. The technology is still in the development stage. Currently the technology is dependant on light penetration. Ideally a computer could remotely analyze the light penetration, and hence the soil size and concentrations ("Surrogate Techniques for Suspended-Sediment Measurement" by Daniel G. Wren, Roger A. Kuhnle).
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