Hydropower has an enviable reputation of being clean, green, and renewable. This was probably true of the earliest installations which ground flour, sawed wood, crushed various ores and treated woolen cloth (fulling mills). The earliest hydroelectric installations were “run-of-the-river”. They simply diverted part of the water flowing over a fall or rapids through their generating equipment – generally a simple water wheel.
Once the easy “run-of-the-river” power sites had been used, the world wanted more. This demand was satisfied by building dams, artificially raising water level, so increasing the amount of power which could be generated at the site.
Some of these dams are monsters:
The James Bay complex 25m to 150m (range over 11 generating stations)
Kariba Dam (Zambezi R. Zimbabwe) 128m
Cahora Bassa (Zambezi R. Mozambique) 171m
Sardar Sarovar (Narmada River) 139m+ number of people relocated not known . . . millions!
Itaipu (Argentina/Brazil) 118m
Three Gorges (China) 181m 1,250,000 people were relocated!
Grand Coulee (Columbia R) 170m
Mica Dam (Columbia R.) 240m
Glen Canyon Dam (Colorado R.) 200m
Hoover Dam (Colorado R.) 220m
Jones Falls (Rideau Canal – 1830) 18m – an early dam which still has a (tiny) hydroelectric plant
Niagara Falls 51m (for comparison)
Victoria Falls (Zambezi R.) 108m (for comparison)
Clearly, the relocation of thousands of people is an environmental issue. The land these people used to occupy and use for their livelihoods now need to be moved to another site. In places like China and India, there is very little land which might be labelled “spare”. These folk must use already occupied land more intensely – or starve! Relocation also occurs in the jungles of South America, or among the smallholders of Africa. More forest must be cleared.
But this is not what I wish to talk about!
Rivers & Lakes
When you look out over a lake or river, it isn’t immediately obvious to you that the river or lake basin is not lined in plastic or asphalt. Occasionally, river bottoms are rock (eg: the French River near Sudbury). However, generally, lake and river bottoms are sand, mud or gravel.
How, then, do the rivers not drain out????
The answer is simple if not obvious. The water table around a body of water is roughly the same level as the water in the lake or river. The water table may actually be feeding the water body (a “gaining” river), or, it may be draining it out a “losing” river), or, the two may be in equilibrium.
In some locations, where wells have been drilled and much water withdrawn, rivers and lakes have literally vanished. A small retirement community in Florida was located around a small lake. The retirees had enjoyed some quiet fishing when one morning they literally found their lake gone – dry and empty. A little research found that the nearby City of Tampa had drilled a new well and started pumping days before their lake vanished. The land under most of Florida is “karst” – a very porous limestone. Tampa’s well lowered the water table and the lake emptied. Tampa’s response was typical America. They installed another well and pump and simply re-filled the lake with ground water from somewhere else . . . Cheap energy has its uses . . .
The City of Austin, Texas has a district called “Riverwalk”. Withdrawls of ground water caused the river through Austin to dry seasonally. The obvious solution was to pump groundwater into it . . .
How About Putting Water Back Underground??
Why would anyone want to put water back underground? After all, we spend much time and treasure creating wells to pump water out of the ground! Is someone crazy here?
Actually, not at all. The connection between ground water and nearby rivers, lakes is the reason. We can cause these bodies of water to vanish by (unsustainable) pumping of nearby ground water. Moreover, when these (costly) wells run dry as the water table drops; new, deeper wells are needed – which are then pumped dry!
This has been happening for decades in the American Midwest, above the Oglala aquifer. There, crops are planted in circles with circular irrigation system slowly rotating above the crop. However, at many sites the Oglala aquifer’s water table has dropped so low that pumping has become too costly (sale of the crop no longer yields a profit), and the land above is abandoned. This area is not a desert. However, the water is being pumped out of the aquifer faster than rainfall can replace it!
Another place which has dried up is the State of Rajahstan in India’s north-west. It does get rain, but is also home to the Thar Desert . . . The Arvari River used to run through the state. It became seasonal, then in ~1930 it dried almost completely, only running for a short time during the monsoon rains.
The monsoon rains in Rajahstan are not gentle. They drench the land, but often just briefly. Then the water simply sheets off the ground without soaking in. The rivers fill rapidly, often flooding. In particularly dry regions, the ground rarely becomes wet enough to be in a condition to absorb the water falling on it!
The “Rainman of Rajahstan”, Rajendra Singh, persuaded farmers and village folk to construct many small, earthen dams (called bunds, johads, khadins, etc) to trap the water runoff. These “johads” are often arranged in cascade. When one overflows, the water is trapped by other dams below it.
The effect of these dams is to give the rainwater time to soak into the ground. They also reduce erosion. In addition, trees planted at the edges of the ponds provide shade and lower wind speed, slowing evaporation. These trees also supply food for people, livestock fodder, and their roots stabilize the dam.
The effect of many thousands of these dams has been nothing short of miraculous! In 1990, the Arvari River began to flow – permanently – for the first time in 60 years! Moreover, wells which had run dry long before, began to yield water again, greatly reducing the distances people had to travel to obtain it!
In effect, Rajendra Singh, the “Rainman of Rajahstan”, had restored the local water table. He had done this without tapping into foreign aid. By showing the local people that they could massively improve their lives through their own efforts, he restored their pride, and ensured that these projects were maintained and thus became “permanent”.
Unlike our tradition of storing water in mega-dams, the Rajahstan project filtered water (through soil) first and stored it underground, safe from evaporation and contamination by cattle!
Rainman, Rajendra Singh is a saint!
From “A River Runs Again” by Meera Subramanian
Unfortunately, it is less easy to see how this approach might be applied to the dry American “west”. India has an abundance of cheap labour; moreover this labour worked without pay because they were convinced that their efforts would improve their lives. There were also old folk alive in the region who had memories of a flowing Arvari River, so could help convince people that this could work.
In the southern coastal City of Chennai, aggressive groundwater pumping had resulted in salt infiltration of many wells. “Water Woman” Shantha Sheela Nair got a bylaw passed requiring all rainwater runoff from roofs to be directed into the soil around or under buildings. This recharged the groundwater, long dehydrated by acres of paved roads whose sewers shot the rainwater directly into the sea!
In effect, Chennai’s rooftops had become its “johads”!
From “A River Runs Again” by Meera Subramanian
What About Dams?
Imagine a river basin in equilibrium with the surrounding ground water. When someone erects a dam on this river, the water table above the dam rises (as the new lake forms), and the water table below the dam falls as the water level in that part of the river (presumably) drops. It must do so while the dam is filling.
This development can affect wells many kilometres distant from the new dam. Groundwater recharge zones may fall below the water table drying distant wells permanently. On the other hand, above the dam, terrain may become waterlogged with the rising water table.
In a curious incident, a factory was built beside the (Russian) Volga River. This factory was designed to machine high precision tubing of great length, and to a very high degree of accuracy. Accordingly, the factory was put on top of a large, thick concrete slab. In effect, the slab formed the bed of a giant lathe. The precision tubing is machined using this huge lathe.
A dam was built on the Volga downstream of the factory. As the water level in this dam rose, the land around the factory became soggy. In time, the concrete slab deformed slightly. As a result the factory was unable to work as efficiently as it was designed to do.
This factory was making pressure tubes for the latest Soviet nuclear reactors – a Pressurized Water Reactor. Because this factory was unable to keep up with demand, the nuclear reactor built at Chernobyl was an older design; the RBMK, graphite moderated reactor. Yes, this was the design which failed so spectacularly . . .
Most African Rivers are very full during the rainy season and barely flow in the dry season. This has been true for at least a million years. Probably the best known of these is the Nile whose flood refreshed and irrigated the agricultural lands of Egypt from the start of recorded time. Egyptians used to sow their seed as the annual flood was receding – a technique called “recession agriculture”. These crops grew & matured rapidly under cloudless skies, feeding off the brand new soil washed in from the Ethiopian highlands.
The first dam at Aswan was quite low and barely disturbed this age-old pattern. However, the Aswan High Dam was designed to hold back the entire rainy season flood. The water was released gradually, through power turbines, over the year. Irrigation allowed Egypt to greatly expand their agricultural land and to irrigate during the dry season – thus growing at least two, but often three crops in a season.
The downside was (a) standing water in the irrigation ditches facilitated malaria, bilharzia & other diseases, (b) the rich silt which had sustained Egyptian agriculture for 7000 years was now trapped in Lake Nasser forcing Egyptians to apply fertilizer, and (c) rapid evaporation of the irrigation water (under a very hot sun) plus fertilizer caused the fields to become saline – some abandoned; others suffering low productivity.
In time, Lake Nasser will fill up with the Nile’ legendary silt and become completely useless – will not be able to hold the volume of the rainy season. I am not sure what one might do what that happens, but why worry, Lake Nasser is enormous – 550km long and 35km wide (max). It will not fill with silt for at least a century . . .
A Typical African River
During the rains, a typical African river swells to several times its dry season size. For example, the flow over the Zambezi River’s Victoria Falls during the rains is 10 times its dry season flow! During the rainy season, as land is flooded, huge numbers of insects in the soil begin to drown. The fish go nuts over the abundant food supply, using this to power their annual breeding season.
In addition to depositing silt over the drowned land, fish droppings provide additional fertilizer. Of course, the water itself soaks the soil readying it to receive the farmers’ seed.
Once their seed is scattered, and the newly hatched fish have grown, the farmers become fishermen. These fish are dried for use over the rest of the year. The fishermen are now ready to harvest the crop they sowed, and to eat the vegetable matter enriched by the protein they harvested earlier.
Some of these folk are also in the habit of grazing the dry lands away from the river; cows, goats, perhaps camels, with a few sheep (a good desert animal) thrown in.
This has been the pattern for millennia. The fish are primed for it, the insects are adapted to it, and man has taken advantage of the local ecology – everything is in harmony.
A Typical African River Dammed – or perhaps “Damned” . . .
Oddly enough, local potentates begin to acquire dry, low productivity, scrub land a long way from the river. This land may have been used to graze some livestock, but nobody really “owned” it – not until fences begin to spring up – leaving the local fishermen/farmers/herdsmen puzzled . . .
Then bulldozers and trucks moved in. In time the locals learned that a dam is being built. But they don’t understand why. They may be told that the dam will protect them from the annual flood – from which they never before needed or wanted “protection”. They may be told that they will get electricity – which they have never needed before and have limited use for – but it has the ring of modernity . . .
In time the dam is built. When that happens, the river stops flowing below the dam. So there is no fresh silt on the land, and the fish harvest is modest because the drowning insect bonanza isn’t happening. The amount of land which can be sown for crops is very small . . .
Above the dam, the flood is higher than normal, and it does not recede. So no land can be sown. The fish harvest is pretty good though. The following year people above the dam must move because the next year’s flood builds on top of the old one. The people below the dam have been reduced to poverty because they have little crop and little fish – the fish of the area are less fond of stagnant water than they were of running water . . .
Eventually, the dam is full. It turns out that the dry, fenced off, scrub land now has a lakeshore. With abundant water nearby, this land is ideal for grazing – perhaps even for dairy cows. It is also good for lakeshore villas, speedboats and luxury.
Below the dam is where the real action is. The peasants are either hungry or completely driven off because their traditional lifestyle can no longer possible. Their land is acquired by plutocrats, levelled and irrigated for rice or other cash crop. The former peasants are hired as cheap labour on these farms. This land can be irrigated – more or less for free because gravity brings the water to them from the dam. Land above the dam, if it is to be irrigated, needs pumps to raise the water to the land. Not as profitable, unless the electricity is very cheap.
Electricity is now available in the neighbourhood – but only if you can pay for it, and for the power lines bringing it to the customer!
How was this project sold?
Well, the first and best selling point is the hydroelectricity. This is relatively cheap (over the long term), reliable and abundant. If priced right, it may be cheap enough for aluminum smelting. Aluminum smelting now happens in Ghana – but the hydroelectric power plant is underused because the government never installed the full complement of generators and didn’t build power lines to the local potential consumers . . . The growing cities of Africa always need electricity, and if the country doesn’t have coal, hydropower is a great selling point.
Cities are often established along rivers. They have always been inconvenienced, sometimes devastated, by flooding. A dam is often sold to them as a flood control project. “We will capture the rainy season flood & control the flow through the year.” – so no more floods. Also, the river will not dry up seasonally.
To politicians and investors the irrigation sounds very good. They see a market for the cash crops grown with cheap (free?) water, tended & harvested with cheap labour.
Some of these good folk are already wealthy, or expect to become so. They are tempted by the prospect of recreation water. The lake above the dam can have resorts and luxury homes, just like the capitalist world – very tempting!
So that is how the same water has been sold four times over: it is
(3) flood control and
These uses are mutually exclusive:
– A dam used for hydroelectricity must be kept as full as possible, because the head (height) of water determines how much power can be generated, and for how long. An empty dam generates nothing . . .
– A dam used for flood control must be kept as empty as possible so it can accomodate the “100 year flood”.
– If a lake is surrounded by resorts and villas with docks, they will be upset if the water level drops!
– Water passing through the turbines cannot be used for irrigation because to do that it must be pumped back uphill to where the crops are. This costs electricity as well as pressure piping – far more expensive than open ditches filled with gravity driven water.
One More Issue – Silt!
Silt is not just a fertilizer and renewal treatment for farmland. It’s not just a nuisance relentlessly building up behind virtually all power dams. It is also an abrasive continuously acting on penstocks, turbine housings and blades, eventually wearing them to the point of replacement.
What is often forgotten is the role of silt in land building. The characteristic delta forming at the mouth of many great rivers: the Mississippi, Mekong, Niger, Nile, Amazon, Zambezi and others. (Look at their characteristic appearance in an atlas.) The low land now called the Netherlands is very rich agricultural soil deposited over many millennia by the river Rhine. The Rhone has created a similarly huge delta in the south of France around the old Roman city of Arles and between Marseilles and Montpellier.
One excellent example is China’s Yangtze. The world’s largest city, Shanghai (over 24 million people), is built on its silt. Of course, the supply of silt stopped abruptly when the Three Gorges Dam started filling. So now the Yangtze is gradually eroding the silt supporting Shanghai . . .
That’s not the end of the problem. The water around the mouth of the Yangtze supported a huge fishery. The species living in that area liked silty, low-salinity water. Now that the dam is filling, less water flows to the sea and the water is more saline. In addition, the water has little silt. Unsurprisingly, the fishery has collapsed. Doubtless, it will improve as new species which prefer clear saline water move in, but for now, the fishermen return home disappointed.
This is not an isolated case. Much of Egypt’s agriculture happens on the Nile delta. Its silt supply cut off, this is gradually eroding and individual peasant farmers are gradually losing their land. Fish catches in the eastern Mediterranean have declined with the loss of their supply of nutrient-laden Nile silt.
One reason the City of New Orleans flooded when hit by hurricane Katrina was the gradual loss of silt-fed wetlands around the City, particularly those protecting the entrance to Lake Pontchartrain. The Mississippi used to empty into the area protective Lake Pontchartrain, but to facilitate shipping, the river was constrained into a canal out to the Caribbean, cutting off the silt.
On the left are photographs of the Chandeleur islands lying to the south east of New Orleans. These uninhabited islands – created of Mississippi silt long ago – once acted as protection for the city from storm surges, but Katrina almost washed them away. The next storm surge will have almost unhindered access to Lake Pontchartrain and New Orleans.
So, perhaps dams also act as flood promotion . . .!
A few more “small” items . . .
In northern Quebec, a set of huge hydroelectricity projects were constructed; the James Bay Project. This is considered “clean” electricity. However, the new lakes formed leached mercury from the local rock. This mercury, converted to an organic form: methylmercury, has made their fish and any creatures eating them, toxic for people!
The First Nations inhabiting this land have been warned that they should eat tinned meat & fish instead of traditional foods from their traditional lands. However, nobody offered to supply them with this form of protein!
Is this the only instance of artificial lakes dissolving toxic materials out of the rock & soil they now cover?
Many large dams have been built in tropical regions where temperatures are high year-round. Clearly, water evaporates from the artificial lakes created by the dams.
Lake Nasser, formed behind Egypt’s Aswan High Dam, is located in the eastern Sahara Desert. Situated in a particularly dry desert, it loses a lot of water to evaporation. One study calculated evaporative losses of 7mm/day; this translates to around 15 billion cubic metres per year. The annual discharge of the Nile is 89 billion m3, so the Aswan High Dam has decreased the volume of water supplied to Egypt by 17%! Together with seepage (loss to the water table), 25% of the Nile’s annual flow is lost before it reaches Egyptian farms and people!
America’s Glen Canyon Dam created Lake Powell. This is the 2nd largest dam in the USA and located between dessicated Nevada and very dry southern Utah. It evaporates approximately 10% of the annual flow of the Colorado River. Lake Mead (behind Hoover Dam) is entirely in the southern Nevada desert, and must lose at least that much water! It has been estimated that the various dams along the Colorado River cause the evaporation of a quarter of the flow of the Colorado River!
California is not in its 4th year of unprecedented drought. Many California ski centres had no snow for 4 years. They do have snow this winter, but less than “normal”. Even this winter’s heavy rains have not come close to replenishing the state’s desperately dry reservoirs. Against this background, one might conclude that there are far too many dams, causing the wanton loss of far too much water, along the Colorado River!
(3) Flawed Economics!
In Africa and other regions where peasant agriculture rules, the output of small enterprises is simply not logged. So when a peasant exchanges a stalk of bananas for a basket of fish, only the neighbours & relatives of the two traders know. The government & its economists definitely do not know and have no easy way to discover the economic value such exchanges represent.
So when irrigated rice plantations, commercially grown maize, dairy farms and greenhouses filled with flowers or tomatoes spring up on what were once peasant farms and pastoralists grazing land, government economists log their output as a positive contribution to the nation’s GDP. To this is added the hydroelectric power, and tourism associated with the beautiful lake behind the shiny new dam. There is no entry on the negative side of the ledger. However, the lost fishery and the peasant impoverishment are still there, even if nobody notices!
(4) Do Dams Provide Flood Prevention, or do they just Threaten Much Bigger Floods?
The Mosul dam on the Tigris River is in danger of collapsing. Of course, people have been building on the flood plain simply because the dam exists. Its collapse would flood Baghdad and other cities along the river. Moreover, the flooding would extend well beyond the flood plain associated with the “normal” river flood prior to the construction of the dam. And then there are a number of Himalayan dams built in active earthquake zones . . .
Perhaps this essay should have been entitled: Hydroelectric Power – peeling away the green paint!