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Floods of rain!

September 29, 2011

Chiang Mai has experienced its richest rain fall in a long time. At Dokmai Garden we have so far measured 319 mm in September, which is 69 mm more than the average measured at Chiang Mai airport. This equals three additional heavy rains compared to the average year. Yesterday in the morning we received 48 mm in just 90 minutes, resulting in closed roads, schools, train stations and even some casualties. Dokmai Garden is well fit to cope with this although a current visit demands good foot wear due to the soggy conditions, but it is green, and I discovered a new wild orchid yesterday, probably another Cymbidium aloifolium. I think the origin might be our ancient mango. I do not know what is up there.

If you wish to cope with the water, here are some useful advice:

1. Do not cut down all trees. Trees bind the soil and slow down the force of water, preventing flash flooding.

2. Chiang Mai is full of quarries to trap water for the dry season. This is good and a tradition since the first Thai speaking people arrived in the 13th century. However, do not plant trees in the slope only. The weight of the rains may make them fall down as their roots are gripping a jelly-like soil only. Also plant some trees 5 and 10 meters before the edge of the quarry. No tree can withstand a stream lead into a quarry. Such a stream will cause terrible erosion. You need to redirect the stream around the quarry, or make a concrete inlet.

3. An excellent erosion control is bamboo. Bambusa vulgaris, the golden variety, forms a thick root system. The bamboo culms are very tall though so beware of roofs and power lines. Smaller species might be more useful in such conditions. I have already been asked to put together the outlines for producing bamboo commercially. It is a clever thought as everyone in town will start thinking about soil erosion now. Unfortunately I am too busy with the orchids.

4. Avoid heavy dripping. Let the ground vegetation grow tall in August and September to reduce the power of the rain drops battering the soil. Add leaf litter (do not burn it) which also reduce the power of the rain drops.  The leathery leaves of propeller trees (Dipterocarpus spp.) are perfect. This is especially important if you repair damaged soil. Remember, rain can make holes even in stones.

5. Keep an eye on your garden, make frequent checks, also during the rain. Weather forecasts tend to be general and so they are not very useful for the erratic Chiang Mai weather pattern. One district may receive 100 mm in a day, while the neighbouring district may receive nothing. Simply be aware that during August-September it can rain heavily. However, weather forecasts may tell you more about larger weather systems such as declining typhoons: http://news.bbc.co.uk/weather/forecast/1251

Good luck!

Eric Danell

Blue or silver bamboo (Dendrocalamus sericeus) is strong and beautiful, perfect for keeping a bank in position. Beware of its height though, 15-20 m!

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2 Comments leave one →
  1. September 29, 2011 4:32 PM

    Very good points. If we want to prevent even more frequent flooding we need to protect the forests everywhere in the Ping river basin. I fear that development of the region will only make the flooding worse in the years to come.

    • September 30, 2011 8:41 AM

      Yes, we need to focus on spreading the message trees are vital for preventing erosion. Most land developers simply eradicate everything in their plot, build some houses, accept the cash and leave the new home owner with the problems. The knowledge about using trees to prevent erosion is ancient, but many people are unaware and are so surprised when their houses fall into the abyss. Every new generation needs to be educated. Teachers in physics and biology should combine their efforts. Maybe bring children to an eroded plot and discuss what happened and what could have been done.

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