Geography of the Dão valley
The change in altitude and longitude between the fonte and the foz make for a difference in climate on either end. There is a 684 mtr height difference between the fonte and the foz of the Dão and the fonte is located 70km more inland than the foz at the Barragem of Agiuiera.
When we started walking on April 29th the oak trees by the fonte were just about to leaf out while the same kind of oak at the foz had already completely leafed out.
The Dão valley consists of two different halves.
The two halves meet right in the middle at km #50 of the river. This difference and split is due to a few factors.
1. Right in the middle of the Dãop valley there is a geological and manmade bottleneck by Fagilde & Prime. Here the valley is very narrow and with steep hillsides, the N16 passes through and the A25 viaduct over this narrow passage and the Barragem (dam) of Fagilde is located right above to the east of these roads. The passage of flora and fauna is very compromised here because of the roads and the dam.
2. The difference in human activity (villages, towns, industry) between the North East half (less and at a larger distance) and South West half (more and closer to the river)
3. The damage of the fires of 2017 that burned through the valley from Santa Comba Dão up to Alcafache and S. J. de Lourosa. (10 km below Fagilde)
4. The increase in presence of monocultures and invasive and non-native species (Acacia Mimosa and Eucalyptus) that starts around the Barragem of Fagilde.
In the first half there is more space for nature including oak woodlands and riverside woodlands, and the assault on nature has not been as intense resulting in more habitat for species. This does not mean that the second half is not interesting or that nature is gone. The pockets are just smaller and more dispersed and, where it can, nature is recovering.
Changes in the color and smell of the river.
Christal clear - from fonte till just above Penalva do Castello
First small foam patches and non-organic smells (soap and sewage) – around Campina (P. d. Castelo)
Yellowish / rust color transparency – by Trancoselos below Penalva do Castello
Brown grey tint and less transparent – starting at the Barragem of Fagilde and all the way to the foz.
Lots of soap patches between mouth of the Barragem of Fagilde and Fontanheiras
Christal water at km #8
Rusty color and some foam at km #35
The quality of the Dão valley as an ecological corridor.
As most of the North of Portugal the Dão valley is made up of a diverse landscape with a mix of lots (use of soil) for grazing, endemic oakwood forests, planted forests (pines and eucalyptus mainly), stands of Acacia Mimosa, shrub-lands where trees have not been able to come back after fires, granite bedrock surfaces, vineyards and other types of agriculture. In the mix of all these different types of land use we looked specifically at the quality of the Dão valley as an ecological corridor.
Ribbon of trees along the Dão
Dão at Ponte Dum
What stands out:
As mentioned before the ecological corridor is not obstructed by any city or even village. And most villages and cities are located on the hillside rims and at least a few hundred meters away from the river. Which, for a river that is 100 km long, could be quite unique.
Based on what we saw the river has a line of trees along most of its course , mainly Alders, Ashes and Mimosas, which means that the waters can remain relatively cool and there is some protection for animals to move along riparian gallery.
All along the valley there are many many oak forests, especially in the side valleys of the creeks that feed into the Dão. Also in the 40% of the Dão valley that burned on those fatal days of October 15 and 16 of 2017, the oak forests either survived or are now well on their way back to reestablish. The contrast between the remaining oak forests and the surrounding burned pine, mimosa and eucalyptus stands is big. The fires just could not make their way through these cooler and more humid forests.
This fact, that there are many oak forests, means that endemic species have habitat. It would be worthwhile to map these valuable habitat areas, measure their size and do research into how much wildlife and biodiversity is supported. What would be even more worthwhile is to protect these areas and develop a project in support of the ecological corridor of the Dão valley. The INCF identifies river valleys as Ecological Corridors but that does not seem to have any influence on what is allowed in the Dão valley as I have seen many eucalyptus plantations right down to the river. So it is up to anyone who wants to dedicate themselves to this task and get the right people and institutions together to make this happen. It is my wish to make it a core mission for the Caminho do Dão to contribute to the protection of the Ecological Corridor of the Dão valley. I just have to figure out how.
A mix of woodlands by P.d.Castelo
The oak forests around Povoa Dão survived
Human presence in the Dão valley -
The Dão river does not flow through the heart of any city or even village. The only two settlements it flows through, with buildings directly on the river on both sides are Termas de Alcafache and Caldas de Sangemil. Of all cities and villages on the Dão Santa Comba Dão has the most geographical and infrastructural connection to the Dão. Other closely built villages are positioned a bit away from the river and don’t seem connected. This distance between where people live and where the river flows must have an effect on the way people relate to the Dão …… something to think about. ‘That river down there’. The mystery of the valley of the Dão.
The effect of the fires of 2017.
Silgueiros - Dão Valley
Many factory farms (poultry and pork) in the first half of the Dão valley.
Waste and non organic materials in the Dão valley.
The closer our paths through the Dão valley are to villages the more the paths are filled with building debris with tiles, concrete, building stones etc. including lots of plastics and other non-organic materials. With the sun and rain the plastics will deteriorate and wash down into the Dão.
Everywhere we go plastic ribbons, used for marking cycling and hiking events, are left hanging in trees and shrubs. EVERYWHERE
Around agricultural lands we always see a lot of discarded and deteriorating agricultural plastics.