Hydrology

Muddy Waters: Impacts of Damming the Amazon's Principal Tributary

Organized by Glenn Switkes
Edited by Patricia Bonilha

• March 2008 World Rivers Review
  

The central assumption governing the design and operation of all major water projects has just been declared dead by a group of leading water and climate scientists. Designers and builders of dams need take note.

The scientists, led by Paul Milly of the US Geological Service, explained in a recent article in Science that our dams, floodwalls and sewers have been designed and operated under the assumption of "stationarity" - that natural systems fluctuate within a defined set of extremes that can be estimated from past experience. But climate change means "stationarity is dead" for water resources planning, the scientists say.

Lori Pottinger

from World Rivers Review

The book "Disconnected Rivers" by Ellen Wohl (Yale University Press, 2004) reveals how human activities have impoverished US rivers and impaired the connections between rivers and other ecosystems. The following excerpts describe the natural interactions that make for a healthy river, and an effort to restore the channelized Kissimmee River in Florida.

From a hydrologist’s point of view, the Feasibility Study of proposed hydroelectric power dams on the Cunene River has some serious deficiencies. In order of importance, they are: 1) The study is organised so as to be virtually inaccessible to even a careful reader. Separate pieces of the same subject matter are scattered in illogical places throughout the voluminous corpus of the study. 2) Flow data, and estimations in the absence of data, are of low reliability. The entire hydrological analysis is based on the premise that a meagre 12 year streamflow record from a location 200 km upstream of the dam site can be linked with a longer record from another river basin to synthesise a reliable theoretical streamflow data base with which to assess the viability of a 1.9 billion dollar hydropower project. This proposition is shaky at best. 3) The analysis of the effects of changes in the river’s sediment regime as a result of building the dam are incomplete and ignore the most important issues, such as increased degradation downstream and upset of the sediment regime in the delta. 4) The study lacks a definitive appraisal of the thermal and nutrient regime in the reservoir and river. The potential of drastic changes in the temperature, oxygen and nutrient regimes of the reservoir and lower river to upset existing ecological and cultural relationships have been naively understated. These points are elaborated below.

The conclusion is that the Feasibility Study is not a sound basis for evaluating either the costs or the benefits of the project, nor for proceeding with major financial or other irreversible commitments to the project.

Report Reveals How Uganda Dams are Draining World's Second Largest Lake

A report by an independent Kenya–based hydrologic engineer confirms that over–releases from two dams on the Nile in Uganda are a primary cause