Sediment exchange between the flood plain and channel
exceeds the amout released by the river each year.
The main methods of this exchange are: band erosion,
bar deposition, settling from diffuse overbank flow, and sedimentation
in flood plain channels.
The combined exchanges of sediment trasport define a
"sediment budget" which the researchers calculated by analyzing flows at
10 different places along the river. They estimated an average of 2070Mt
per year of sediment is exchanged, which they broke up into four groups.
Sediment entering the channel from bank erosion ~1570Mt/yr, sediment transferred
from channel transport to bars ~ 380Mt/yr, channelized flow in flood plains
~ 460 Mt/yr, and 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." There is both a net
accumulation on teh valley floor and a net accumulation deposited in the
delta plain each year.
Importance of the Article:
Understanding this accumulation of sediment over time can be important to us in understanding where pollutants such as mercury wind up so that we can look for effects in such regions. Also, it is important to understand the flow of nutrients provided by the regular deposition of sediment so that we can understand how a change upstream in sediment collection may effect the ecosystems surrounding the river.
Each year the Amazon transports 1240 Mt of suspended sediment from Andean erosion plus 3200 Mt of reworked flood plain sediments to the delta plain. There are unique erosion and deposision patterns in different parts of the river. In general, unpstream there is sediment erosion in the main channel and deposistion in the flood plain channels (which are an order of magnitude smaller than the main channel). This leads to what is known as "scroll bar topography." It is characterized by hundreds of long narrow lakes. Oxbow lakes are covered in this area and so quickly vanish. Further downstream, on the other hand, the channels are restricted by stabilizing, long term levee building, and flood plain construction is dominated by overbank deposition. This burries the scroll bar topography and leads to a flat flood plain covered in a patch work of large, shallow lakes. This flood plain is recycled in less than 5000 years, and even faster upstream.
The goal was to develope a method to measure time duration of rainfall, rather than just the amount, thus allowing researchers to see if rainfall was constant or came in short duration high intensity bursts. Rather than collect samples at regular time intervals, the researchers proposed a method of collecting times at which samples reached certain levels (0.2mm in this particular experiment). By having no data for a long time indicates there was no rain, where as previously, the data of there being no rain was recorded. This new method saves data storage space.
Importance of the Article:
Implimenting this method of rainfall monitoring in the
Amazon Basin Rainforest would help us to understand if there is a high
or low danger of flash flooding, which causes higher erosion rates than
steady rainfall. If there is in particular areas, it might be worth looking
into how logging in that area will affect the ecosystem as opposed to logging
in an area with steady rainfall. Also, does the amount of vegitation relate
in anyway to the patterns of rainfall?
Reservoirs have both positive and negative effects on the upstream and downstream environments due to the modification of the natural flow conditions. The research was to determine which sites would be the most feasible and environmentally friendly for hydopower from regulated flow. They simulated water quality in reservoirs and looked at the characteristics of some hydropower developments which already exist. Considering the possiblilities of forest flooding and recovery time, gas formation, eutrophication, etc and made the following conclusions. Reservoirs and thier effects include high temperatures with little to no variation in temperature throughout the course of a year, forest flooding, critical situation in reservoir filling (from the sediment dropped when the water slows in the reservoir), short residence time, eutrophication, gas formation, corrosion of equipment and worsening of water quality downstream. One possible improvement that would balance out these negative effects is hydraulic equipment to reaerate the reservoir.
Basically with the current technology the impacts of hydrolic
power are too large, cost/benefit is not good for our overall goal. However,
in order to minimize the use of hydrolic power, it is necessary to find
a feasable alternative. My knowledge of this is limited, so all I can to
on the matter is suggest that hydropower be used in the most efficient
way: have the power produced be used near the area of production to minimize
losses over long distances of wire; use smaller plants that have less of
an impact on the surrounding environment; use the optimal placements for
amount of power recieved from a given amount of water (high flowrates,
perhaps a steeper area); etc.
Because of a concern of the possible effefts on increased agriculture on the life of hydropower reservoirs and small or medium sized dams, erosion and sedimentation risks were assessed for Brasil. The conclusions were definitions of nine types of sediment risks for Brasil based upon suspended sediment yield. Risk of erosion was very high for some provinces (Rondonia) and risk of sediment deposision was high for others (Amazon flood plain bed). Further study recomendations include "erodibility studies of soils under different plant cover management conditions"..."in order to establish mazimum allowable critical erosion rates."
Importance of the Article:
To understand how conversion to agriculture of certain
areas will affect the Amazon Basin as a whole it is necessary to understand
which areas are of higher erosion risks from development.