GEOPARK PROJECT 644015 H2020 MSCA – RISE.
THE ZAT VALLEY IN MARRAKECH (MOROCCO).
INITIAL VISION OF TYPES OF POTENTIAL NATURAL RISKS EXISTING IN THE ZAT VALLEY IN MARRAKECH (MOROCCO) – NOVEMBER 2015.
CERDAN INGENIEROS S.L.
INTRODUCTION. GENERAL CONCEPTS.
The social and economic impact of natural hazards, both in developed countries and those developing, continue a trend increase in the coming years. This fact is a consequence of the increasing severity of these natural phenomena to climate change combined with a socio-economic vulnerability of the territories when the political determination is inadequate in dealing with this problem. Although these phenomena are impossible to avoid, that does not mean that they must admit with resignation. We must act preventively and proactively, expanding knowledge of natural disasters, establish corrective measures to the foreseeable impacts and properly planning the uses of the territory. The objective is none other than to minimize the losses in human lives and economic.
To begin with, we should talk about natural risks when these phenomena can affect the population and its activity. The concept of risk estimates the probability of damage caused by a natural phenomenon, as the combination of the dangerousness of this natural phenomenon, the vulnerability of the elements that can be affected and of their exposure. The risk is expressed by the relation:
A danger natural geological, hydrometeorological and biological or induced by human activities carries an associated hazard and it increases depending on their location, intensity magnitude and frequency probability
The vulnerability is defined as the expected damage in a structure to the action of a phenomenon.
The exposure is expressed as the elements, people, goods and services potentially affected to the action of a hazard.
NATURAL RISKS IN MOROCCO.
Because of their geographical and climatic variability, Morocco suffers natural and environmental disasters so it posed significant economic losses and human lives. According to the Centre for Research on the Epidemiology of Disasters (CRED)¹, over the last 20 years (1994-2014) the damage from devastating floods, major earthquakes, intense droughts and desert erosion were a total of 1,842 dead, 632,350 affected and damage about 1,900$ million.
Significantly important they are the riverine floods that occurred in the Ourika Valley (1995), the basin adjoining Zat river which affected 35000 people, and the quake with a 6.2 magnitude, that struck on the 24th February 2004 in the Alhoceima area.
NATURAL RISKS OF THE ZAT VALLEY. THE FIRST OBSERVATIONS.
From the last expedition in November of 2015 in the Zat Valley, we proceeded to a first contact on the field to determine, on a preliminary basis, the vulnerabilities of the territory of a first sector, to be included in the Geopark project; the evidences that they are observed that can be used to deduce the usual hazard phenomena in the area. All this will be used to determine the areas of natural risk before an exposure scenario these phenomena.
In this area of the northern slopes of The Atlas, the floods have a torrential dynamic at the head of basin, causing the flooding of the middle and lower river, very fast and with sudden floods of the “flash flood” type. They are accompanied by hailstorms in areas and they can be extended along of 10 to 50 km, with a duration between 3 and 6 hours, and which can be repeated up to 10 times a year
In the images 1, 2 and 3, are observed the damage in the infrastructures, it caused by these natural dynamic processes around the population of Tighdouine; this damage is compounded by the simplicity in the design and execution of these infrastructures. It was observed in the retaining walls to using concrete in mass, without classification arid and neither metallic armour. Likewise, the pillars of the structures are located on foundations based on surface footings.
These foundations that undoubtedly they should be deep and not superficial, in the energy of river flood, they don’t resist the processes of scour.
Although there is not record of damages significant per development of landslides on a large scale, is certain that the multiplication of specific phenomena scattered throughout all the area can be a “drip” of damage on roads and paths, with a risk of loss of human lives which will increase as you increase the traffic of people in this area of planned touristic promotion.
The nature of these phenomena is largely due to the existence of banks of rock with variable features of discontinuity (stratification, joints, faults, schistosity, …) and orientation (direction and dip).
Along mountain’s roads and paths have been observed evidence of processes to bending and buckling in vertically oriented layers. The human activity at the time of opening new routes for the transit of vehicles, it is an enhancer element of instability if corrective measures are not taken into account and protection.
Once we enter inside of the Geopark, where the landscape fits the course of the river Zat in reliefs of high slope, environment to the ways that lead to the heart of Tizirt, have also been observed evidence of avalanches of rock and soil “debris flow”, in the form of alluvial fans.
¹ Centre for Research on the Epidemiology of Disasters (CRED). Emergency Events Database EM-DAT. http://www.emdat.be/