At end of day today Mark had reached the valley of the Alberche, a tributary of the Tagus and was about 50 miles south west of Madrid. The view of today's route (left) doesn't give much away. The snow capped peaks are the Sierra de Gredos which include the highest peak in central Spain - Pico de Almanzor (2600m) . It is worth remembering that altitude causes a temperature drop of 6.5 degrees for every 1000m. Thus the summits of the Sierra will be around 10 degrees colder than the plateau from which they rise giving a sort of sub Arctic climate in winter. Cutting across the area from east to west south of the mountains is the Tagus but for most of its course, except where it has been dammed, it flows in a narrow valley with little in the way of a floodplain. From 'this' height, therefore, the landuse which usually helps to identify a river's course is just not visible. The good news, however, is that the nature of the valley makes it very suitable for the construction of reservoirs which will provide a theme for today's posting.
Once across the hills, Mark descended towards the Tagus . There are very few large settlements along this part of the river and I do wonder whether it is the nature of the valley - the fact that it is quite constricted -which has hindered communications an settlement. This lack of large settlements, combined with the fact that Mark had to use minor roads, meant that there have been fewer points of reference today.
I have decided therefore that I will follow a theme rather than a route for the remainder of today's journey; the theme being the river Tagus and the management of its waters. The Tagus at just over 1000 km long is the longest river in the Iberian peninsula but it pales into insignificance compared to some of the rivers we have looked at recently in the US! As mentioned already, its course through Spain is fairly constricted - it doesn't have much of a flood plain until it enters Portugal. Just before the border is the largest dam and reservoir along the river - the Alcantara. The waters held back by the dam extend a full 50 km upstream.
With the Alcantara dam downstream to his west, Mark met the Tagus just to the east of a small dam which holds back the waters of a tributary of the Tagus. Its purpose is just visible on the image below but clearer on the next...