Waterjettting 19b - California gold mining

While mankind has directed the flow of water against earth and rock faces for millennia, as a way of eroding and removing material, it was not until the days of the Gold Rush in California around 1850 that the idea of confining the water into a hose, and through a nozzle crystallized.

Gold was originally found in the gravel in 1848, when James Marshall was helping John Sutter build a sawmill on the banks of the South Fork of the American River, in what is now Coloma, CA.

Figure 1. Sutter’s Mill on the American River (Replica by California Parks ).

The news that gold had been found in the tailrace led into what has been referred to as the greatest mass movement of people in the Western Hemisphere, as people flocked to California over the next few years, during the period of the California Gold Rush.

Figure 2. Location of Coloma, CA (red circle) relative to Sacramento and San Francisco – Lake Tahoe is by the 395 sign in the upper right. (Google Earth)

As the prospectors panned the gold from the stream beds, so they moved north east along the valleys and rivers, seeking the sources of the gold particles that millennia had washed down from the Sierra Nevada. One such source was found at American Hill, just north east of Grass Valley. Here the gold was found in beds of a weak sandstone, lying relatively close to the surface.

Figure 3. The American Hill Diggings, with plaque. The original height of the hill can be seen in the background.

The gold settled to the bottom of the sandstone, and so the miners would tunnel into the side of the hill, seeking to find the richest layer. Unfortunately as you dig out the bottom of a hillside, the overlying rock has a habit of falling down, with mildly fatal results to those caught in its path. This made mining somewhat dangerous, given the soft nature of the rock as Edward E. Matthison found when he was nearly buried when he was working the property. So with partners, he decided that a more remote method of digging out the gold was needed. So, with the help of a local blacksmith named Miller, he fashioned a nozzle on the end of a canvas hose he ran from a water reservoir at the top of the cliff (initially a nail keg) and used the resulting stream to wash the ore (and overlying rock) into a channel that was later turned into a flume, with a series of strips to catch the gold.

Figure 4. Early hydraulic mining

The method had many advantages since, in the process of washing the rock from the solid it was broken down into individual particles. This separated the gold, sand and clay particles, so that while the gold particles would be trapped in the flume, the lighter sand and clay particles would be carried further downstream with the water. By 1853 they were paying a water bill of $153 a week (with water at $0.75 per miners inch this meant they were using 2,000 gal/min) but making the four partners a profit of $50 a day. Larger and larger monitors (the name given to the nozzle and pivoting assembly) were built, throwing water at greater distances, and mining at much faster rates.

Figure 5. Monitors at work at the North Bloomfield mine.

This, in turn, required increasing amounts of water, and this was carried in flumes down through the Sierra Nevada, with agreements being made between companies for distribution, collection and the passing on of water. The nozzle diameters of some of the larger monitors grew to more than 8 inches, and they were capable of mining tens of feet from the operator.

Figure 6. Later design of monitor. The wooden beam usually had a box holding rock on the other end in order to balance the weight of the nozzle section.

The nozzles were made longer, as they were made larger, in order to get the jet to throw to greater distances, but this made steering and control of the jets more difficult. The gooseneck swivel was invented in 1855 to help swivel the nozzle, and a monitor operator noted that when he stuck his shovel into the stream of water it deflected the nozzle. This was Dave Stokes at the Malakoff mine and led to the invention by his Supervisor, Henry Perkins, of the rotating system for sprinklers that is still used to this day.

Figure 7. Modern rotating sprinkler showing the deflection plate. (Aliexpress )

The largest mine in the region was the Malakoff, and in the region around it there were some 425 companies operating and, between 1871 and 1880 they produced $121 worth of gold (at the price of the day).

But there was costs to this operation outside of just the mining ones. For while the gold was captured in the flumes, the sand, and more particularly the clay, was carried in the water until it became less turbulent. And that was when it reached the Yuma, American and Beam rivers flowing out of the Sierra Nevada and down towards Sacramento. As the water slowed, so the clay precipitated out, and the river beds filled with sediment. Thus, when the rains came, the water overflowed its banks, flooding the neighboring fields.

Foregoing the fact that it was the mining that had brought the farmers and many others to the region, the floods were not acceptable, and following the floods of 1880 there was an increasing effort to contain the mining sediments. This led to the court ruling by Judge Sawyer in 1886 restricting the practice of hydraulic mining, and the technology fell into abeyance. It was restarted at the time of both World Wars, but in recent times there was only one small mine that had been “grandfathered” still in production. Its role in developing California is not greatly recognized at present, and the remaining legacy is more seen in the vertical bluffs and large flat areas of mined sand that are left north of Grass Valley, together with the old wooden water flumes that still thread their way around the edges of the valleys.

Figure 8. View of the Malakoff Diggings

I’ll talk more about the spread of the technology next time.

The Nile, The Guardian and disaster without climate change

There are times when the corruption of the press by the mantra of “climate change” becomes a little more obvious than usual. So it is with the piece that appeared in the Guardian last Friday concerning the coming disaster to Egypt from the changes going on in the Nile Delta. To condense the story into a nutshell, it deals with the declining prospects of the Delta - the main agricultural resource for Egypt - both as it is currently evolving and looking forward from that into the future. You can see the influence of the Nile, and the Delta, (the green bits) in this overview shot of Northern Egypt (mostly the brown bits) from Google Earth.

Nile Delta and Egypt from Google Earth

The story begins with the story of the farmer Maged Shamdy, and his perceived fate.

"We are going underwater," the 34-year-old says simply. "It's like an occupation: the rising sea will conquer our lands."

Maged understands better than most the menace of coastal erosion, which is steadily ingesting the edge of Egypt in some places at an astonishing rate of almost 100m a year. Just a few miles from his home lies Lake Burrulus itself, where Nile flower spreads all the way out to trees on the horizon. Those trunks used to be on land; now they stand knee-deep in water.

Maged's imperial imagery may sound overblown, but travel around Egypt's vast, overcrowded Delta region and you hear the same terms used time and again to describe the impact climate change is having on these ancient lands.

The only problem is that the rest of the story documents how it is everything but climate change that is causing the problem – which doesn’t of course stop the author of the piece, Jack Shenker, from making the claim. So let me, as I did for the Bangladesh Delta, explain, with the aid of the odd peer-reviewed journal article, what is causing the problem – it isn't climate change - but in a word or four it comes down to overpopulation and the Aswan High Dam.

Let’s start by explaining how a delta system works –whether in Egypt, Bangladesh or Louisianna. The delta lies at the seaward end of a long river that picks up eroded soil carried into it from its feeding and surrounding tributaries, or eaten away from upstream by its own passage. Seasonally the river floods over the delta, and in so doing, as the water slows, it deposits soil on the surface of the delta. You can actually see effects of previous climate change by the changing nature of these sediments. In the case of the Nile, the floods come about following heavy rains in the Ethiopian highlands and Sudanese basin typically in July. August and September. Lands could be flooded to a depth of up to 5 ft, and would be inundated for about a month and a half. In that time the sediment in the water would settle out as silt, the water would flush out any residual salts in the soil, and would prepare the soil for the subsequent planting of crops. This process has provided fertility and water to the Delta for thousands of years. On average the rains in the headwaters of the Nile removed around 0.2 mm/yr of soil and this was deposited in the Delta to an average thickness of around 1 mm/year. Interestingly across the Mediterranean at Venice, Day et al showed that this type sedimentation is anticipated to provide enough land build-up over the next 100 years to mitigate even the sea rise anticipated by the IPCC at some sites.

However, as the article notes, in 1970 the High Dam at Aswan was built, and this captures all the Nile sediment (between 40 and 132 million tons a year) which is now filling Lake Nasser behind it. Although, with the Lake being some 300 ft thick, and 500 miles long, it may take a long time to do so. But now that fertile material is denied the Delta.

So that is the first part of the problem. The second part is that the sediment of a delta will normally compact over time, forcing water out of the lower members, and thus gradually lowering the top of the overlying surface. Where the land is regularly flooded that sinking is matched by the new soil that floods over it, but it is now about 40 years since the soil stopped flooding over the land, and the amount of soil missing is becoming significant. Hence, as the quote above notes, the gradual sinking of the trees into the water of the lake.

The lowered land levels also make the land more vulnerable to sea erosion. Smith and Kader showed that this can be tied to the reduction in sedimentation.

Although coastal erosion is a serious problem along the Egyptian Mediterranean Coast, it is localized at specific areas. These areas have undergone slow to moderate erosion since the turn of this century as a result of natural decrease of the River Nile flow and as a result of increased number of structures across the Nile. In a post High Dame phase, these areas eroded at accelerated rates (3-5 times the rates before the Dam).

Lake Nasser from Google Earth – at the other end of Egypt (the yellow line is the border) The High Dam is at B, and this used to be Nubia.

And to get back to the original article for the remaining problems

Today, however, Nile water barely reaches this corner of the Delta. Population growth has sapped its energy upstream, and what "freshwater" does make it downriver is increasingly awash with toxins and other impurities. Farmers such as Maged now essentially rely on waste water – a mix of agricultural drainage and sewage – from the nearby town of Sidi Salim.

The result is plummeting fertility; local farmers say that whereas their fathers spent just a handful of Egyptian pounds on chemicals to keep the harvests bountiful, they now have to put aside between 25 and 80% of their profits for fertilisers just to keep their crops alive.

As the article itself notes the increased population is taking the water that used to irrigate the lower parts of the Delta. This has nothing to do with climate change (except in that the milder conditions of a Warming Period has historically led to population surges) But that doesn’t stop the charge being made.

Experts believe the problem is only going to get worse. "We currently have a major water deficit in Egypt, with only 700 cubic metres of freshwater per person," explains Professor Salah Soliman of Alexandria University. "That's already short of the 1,000 cubic metres per person the UN believes is the minimum needed for water security. Now, with the population increase, it will drop to 450 cubic metres per person – and this is all before we take into account the impact of climate change."

Much before any problem that might be related to climate change shows up, Egypt has a much larger problem, which is the root cause of the above, and which the article points out

With Egypt's present-day population of 83 million set to increase to more than 110 million in the next two decades, the seemingly unstoppable spread of bricks and mortar over the soil is both the most visible symptom of the country's demographic time-bomb and an inevitable response to it.

Perhaps that should, more logically, be addressed first?

Ah, well, enough said.