A Disaster Waiting to Happen?

You don't have to be an expert to realise that the hillside above the Embalse de Rules is on the move - you need only take one look at the N-323 that runs along it.

GRA Rules Unstable HillsideMostly this reservoir is in the news because successive Central Governments have baulked at finding the funds to get the water out of the reservoir and down to the coast where it is badly needed for crop irrigation.

However, this construction seems to be jinxed or just plainly ill conceived.

At the very beginning of the excavation stage, work had to be stopped as the site for the dam wall was sitting on a fault line. Work began again from scratch and finally it was finished and water began to flow in and fill the reservoir.

At the same time the A-44 was under construction and the long bridge that crosses the Alpujarra arm started to sink at one end, so they had to stop filling it and build new pillars to support the bridge.

But that’s not all because the N-323 that runs along the left-hand side of the reservoir has had no end of problems because the hillside below it and above it was moving.

COS N-323 Rules kink in roadEven today there is a kink in the road just up from the dam because the original road slipped down the hillside, so they had to cut into the hillside further. If you look carefully at the photo you can see the remains of the original piece of road.

The N-323 continues to sink in places and each time it is patched up with a touch of tarmac but drivers who hit these steps in the concrete certainly realise they have hit one when they go over them.

If you really want to see something that will make you lose your sleep, take a look at the hillside below the road. When they built the dam they decided to create a sort of mirador situated at the edge of the hillside above the water. There was a parking bay where you could look across the water and admire the view.

The entrance road has been blocked off because the access lane and parking area had literally fallen apart, with the tarmac breaking off in wedges. If you are prepared to work your way down these steps where the surface had dropped, around 1.5 metres in places, you finally reach the parking area. This is evident proof that parts of the hillside is slipping down towards the reservoir and thank God that it is moving slowly… for the moment.

The problem is that we are in the middle of a drought and those cracks are opening up as the baked earth contracts but when, God forbid, heavy rains come, it could accelerate the descent producing a sizeable landslip into the water below.

If tonnes of rock and earth hit the surface of the reservoir in enough mass then it will send out a surge of water right across the surface, right down to the dam wall itself.

Sound far fetched? You may have heard of the Vajont Dam disaster? I’ll quote from Wikipedia:

“On 9 October 1963, during initial filling, a landslide caused a mega-tsunami in the lake in which 50 million cubic metres of water overtopped the dam in a wave of 250 metres (820 ft),which brought massive flooding and destruction to the Piave Valley below, leading to the complete destruction of several villages and towns, and between 1,900 and 2,500 estimated deaths. The dam itself remained almost intact and two thirds of the water was retained behind it.”

Meanwhile, back at Rules Reservoir, a group of scientists have ‘uncovered’ this serious problem, thanks to satellite images that shows clearly this earth movement in the area known as El Arrecife. We use quote marks on the word ‘uncovered’ because this problem has been known ever since the dam project was first set down but seemingly ignored, as might the work being carried out by the scientists, no doubt.

When they came to plan the route of the N-44, they had three choices; the one they eventually used or widening the existing N-323 into a 4-lane autovía, which meant cutting further into an unstable hillside, or building a 10-km long tunnel from Ízbor to just beyond Vélez Benaudalla. The N-323 option would have been a nightmare and the tunnel option far too expensive, so we got a bridge across the arm of the reservoir.

Supporting Pillar Sinks

Supporting Pillar Sinks

However the bridges, as mentioned before, have had problems with earth movements too. Which ever way you look at it, the valley to the west and north of the Embalse de Rules is unstable, be it for a reservoir or for roads.

The dam itself is of a very strong design, using both the gravity construction and the arch construction: a gravity dam is a structure which resists the external forces by its own weight or self-weight, whilst the arched form takes the pressure at the centre of the damn and shifts it to the ends, which must be well anchored into the hillside.

Rules has a problem with the rocks on which one end is bedded, which is why it also incorporates the gravity construction method.

(News: Velez-Benaudalla, Costa Tropical, Granada, Andalucia)

  2 comments for “A Disaster Waiting to Happen?

  1. November 16, 2021 at 6:46 pm

    Chris: your guess is as good as mine, as it would depend how much of a slip there was and how full the reservoir was at the time, but if a large amount of water did go over the lower, middle section of the dam into the river, Vélez Benaudalla is well above the riverbed and not in any danger, I would have thought.

  2. Chris Sewell
    November 16, 2021 at 5:18 pm

    So how much risk does this pose for Velez De Benaudalla

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