The water-supply is good, the volume of the river ranging from 200 to 900 cubic metres a second. Low water lasts from February to April (end of the summer). From May to July the river has sudden and violent floods--an effect of the autumn rains. The curve sinks again in August and September, to rise once more in October and December, when the snow melts on the Andes. The Limay, the upper basin of which contains large, lacustrine sheets, is more regular than the Neuquen, which has very pronounced low-water, as well as dangerous floods in the autumn. The first attempts at irrigation date from 1885, when the canal of the Roca colony was dug. Others were made lower down at a later date. The co-operative groups organized for the administration of the canals have not been quite as successful as might have been expected. The advance of agricultural colonization has been slow. Costly preparatory work is needed to level the ground and organize the drainage, otherwise saline patches form and spread like leprosy at the expense of the cultivable areas. Lastly, the centre of the valley is exposed to floods.[74] [74] The work now (1914) in hand will reduce the risk of floods, and will enable them to enlarge considerably the extent of the tilled land. The Cuenca Vidal, which opens amongst the sandstone, below the level of the valley, on the tableland to the north of the Neuquen, will be arranged so as to absorb the flood-water, and it will feed a canal which will serve the left bank over an area of 100 miles. The waters of the Limay will be available for the lower valley. [Illustration: THE PATAGONIAN TABLELAND (NEUQUEN). _Indigenous vegetation. Rocks eroded by wind._ Photographs by Windhausen, Mining Division. PLATE XIV. To face p. 154.] The chief crops are lucerne, cereals, and the vine. All the efforts and hopes of the colonists are now centred upon the vine. It is for the purpose of extending the vineyards that they are endeavouring to secure more workers. These are a singularly mixed lot, Chileans from the Neuquen rubbing shoulders with Latin immigrants (Italian and Spanish) from the region of the Pampas.