Regular readers may recall Paul Symington’s article about the heavy rains last winter and the damage they caused in our vineyards. Whilst the climate in the port vineyards of the Douro is renowned for being dry, as much rain as we do get tends to occur almost entirely during the winter, so we are likely to receive a lot of rain in a short space of time. Managing drainage when it does rain is critical for several reasons.
First, we want to encourage as much water as possible to soak deeply into the soil, rather than run off, in order to build the water supply for the roots of our vines to draw on during the summer months. Second, we want any runoff to follow a path of our choosing, to avoid damage to the terraces and again to try to ultimately capture the water in some useful place.
To accomplish these goals, the patamares (banked terraces) are carefully sculpted to direct the flow of water in a very distinct pattern. The level terrace surface is in fact slightly sloped backwards, into the face of the hill, to encourage the water to accumulate in a place where it will ultimately soak into the vineyard soil. Additionally, the length of the terrace is slightly arched, or sometimes angled entirely to one end, so that any water that cannot soak in and needs to run off, will be led to the ends of the terrace, and from there into dug-out gutters that run along the sides of the vineyard roadways. In strategic places we open up drains, where the water can empty off the roadway and into underground pipes.
On a recent rainy-day visit to Quinta da Cavadinha (the flagship quinta for our sister brand, Warre’s, in the Pinhão Valley) our research viticulturalist Miles Edlmann was very encouraged to see that although the patamares in the photos are still under construction, this water flow pattern is already in effect.
Above all, we do not want water to accumulate near, or cascade over the lip of any terrace – this is the most damaging possible scenario, as the soil quickly erodes under the rushing water, forming a deep cut in the face of the terrace. In addition, if the talude, the bank, becomes saturated, that could undermine the stability of the entire terrace. In the case of old walled terraces, this kind of accumulation or cascading is even worse. Not only is it heartbreaking to see these beautiful old walls destroyed, but the UNESCO World Heritage status of the Douro Vineyards obliges us to repair the damage, naturally something we would rather not have to do.
Occasionally it isn’t just rain that causes trouble – after a bank collapsed two years running, we felt certain there was something more than the winter rainfall causing the trouble. Sure enough, during the dry summer months we watched the hillside closely and found distinct wet patches in an otherwise dry landscape. We dug down and discovered a spring inside the hill which was keeping the whole area saturated year round. Ultimately we created a stone-filled soakaway space around the spring and installed drainage pipes to channel the water out of the hillside, so the bank could dry out and stabilise. During our recent visit to Cavadinha the spring water was running out from that pipe almost crystal clear, as opposed to the rainwater runoff which was clouded with soil.
Miles was also pleased to see how the dense cover crops between vines in the vertical plantings were preventing runoff and erosion, but the many uses of cover crops is subject for another article.