Month: May 2019

A modern aqueduct project similar in length and capacity to Bradfield in China

The South–North Water Transfer Project, a multi-decade infrastructure mega-project in the People’s Republic of China, ultimately aims to channel 44,800 GL of fresh water annually from the Yangtze River in southern China to the more arid and industrialized north. Of the three channels, the Central Channel is gravitationally driven and similar in size and scope to the proposed Bradfield Scheme from North Queensland to the Murray-Darling Basin at St George.

The Central Route conveys 13,000 GL/year approximately 1,264 km from the Danjiangkou Reservoir on the Han river (a tributary of Yangtze River) at 170 m above the sea level to Beijing and Tianjin at around 50m (1:10,000 gradient). The canal route required the building of two tunnels under the Yellow River, to carry the canal’s flow. 

The Eastern Route follows the course of the Grand Canal, is 1,152 km long, and equipped with 23 pumping stations conveying 14,800 GL/year. The Western Route is planned to connect three tributaries of Yangtze River with huge dams and long tunnels under Tibetan Plateau and Western Yunnan Plateaus. This route is 500km long and designed for 3,800 GL/year.

Mao Zedong discussed the idea for a mass engineering project as an answer to China’s water problems as early as 1952. He reportedly said, “there’s plenty of water in the south, not much water in the north. If at all possible; borrowing some water would be good.” By 2014, more than $79 billion had been spent, making it one of the most expensive engineering projects in history.

No Comments

Categories: Book Bradfield Scheme

The path to sustainable water systems – an intelligent systems approach

Let’s examine the statistical characteristics of a long open half-channel, considering the property of an intelligent system – i.e. responding appropriately to intermittent disturbances to maintain a constant or homeostatic environment.

We have all experienced the intermittency of rainfall, lasting a day or so, and subsequent flooding. We also are familiar with the pleasant and even flow of rivers even though there might be occasional rainfall upstream.

In a long open half-channel we have the capacity to adjust the flow according to the intermittent inputs along its length, and through the storages and controlled outflows, achieve a constant and regulated outflow along its length (see upper image).

Thus, the reliability of water is ensured through intelligent responses to
the variability of the environment and this reliability increases with length of the aqueduct (see lower image).

An irrigation system drawn from a low storage flow, such as a river, increases the variability of the system. That is, when the weather is dry, farmers withdraw more water for thirsty crops thus decreasing the flow even more. When the weather is rainy, little water is withdrawn for crops are they also receive water from the rain, and so the flow is enhanced. In this way, the natural variability of flow in the stream is exaggerated.

It is the enhancement of variability of flows that is responsibile for the environmental deterioration of our rivers and streams in the Murray-Darling Basin and elsewhere. That is, it is an example of systems being pushed beyond their natural variability, reaching breaking points from which they cannot recover easily. Sustainability, on the other hand, requires maintaining the system within its natural bounds.

The presence of a storage dam or weir increases the availability of water during the dry season, but it does not address the central problem of exaggeration of rainfall variability. Consequently, during a dry spell, the water levels in a local dam fall rapidly as demand increases. During a wet spell when water is not tapped for irrigation, the dam over-tops and the excess spills over the floodway. Thus variation is exaggerated. This is an inefficient usage of water resources.

Thus it seems that a fully established open half-channel aqueduct has the capacity to provide reliable water supplies along its length. Due to the capturing of inflows along its length, it can provide a similar average flow at the end as at the beginning (see image), e.g. 2000GL pa in and 2000GL pa out. By contrast due to losses, the volume of flows diminishes with length. By contrast with a pipeline, a gravitationally driven flow requires no energy for pumping, and delivers water long distances cheaply, reliability and intelligently.

Categories: Book Bradfield Scheme

Benefits of the open half-channel flood flow aqueduct

The breakthrough system developed by Leon Ashby for capturing and transferring flood flows in a Bradfield Scheme has a number of advantages over pipelines. The slide above is taken from Leon’s presentation and lists 3 benefits over a pipeline system.

The profile of the system can be described as an ‘open half-channel’ profile. Whereas a typical profile of a river has a single low flow channel and a high flow channel defined by banks at a distance from both sides of the low flow channel. The aqueduct is half of the natural profile as the constructed levee bounds the conveyed water on the downhill side. Up-slope there is a low flow channel and flood flow space as shown in the inserted image.

The system is also more correctly described as a series of connected storages, contained by a levee bank following a contour for more than 100km, before being connected to the next with a short 10m section containing a hydropower unit, and traversing road or rail infrastructure (see insert).

The three advantages of this system over a pipeline for conveying water are:

  1. Due to friction, pipelines permit water to be gravitationally transferred in a fall of only 1m per 1-1.5km or 1:150. The open aqueduct described may convey water up to 100km per 10m fall, or 1:10,000. This allows the open-channel to transfer water over very long distances.
  2. The open-channel collects water along its length, greatly increasing the catchment area over a closed pipeline. Collecting intermittent falls along the length of the levee bank thus increases the mean volume of flow and decreases the flow variability over the length of the channel.
  3. The aqueduct sited along a contour serves a dual purpose as a reservoir, storing up to 1000GL per 100km of water depending on topography and levee height. Pipes inserted through the base of the levee enables the gravitation irrigation of a series of small irrigation schemes down-slope of the levee.

The images shows the increase in catchment area due to the use of an open half-channel between the Burdekin River and Lake Buchanan (red circle) and another potential route for an open half-channel between the Walsh River and Hughenden (purple).

We see that the open half-channel aqueduct can be likened to an artificial river, constructed to divert water across the slope in the desired direction, instead of taking the natural direct downhill path. A lossless artificial river will have the flow characteristics of a natural river, increasing in flow volume and decreasing in flow variability from start to end.

However, the flow would be efficaciously extracted at points along the length so that the mean and variability of flow remains within the optimal operating conditions of the open half-channel design.

Categories: Book Bradfield Scheme