The author of your watercolors, most likely, is a little-known English artist W. Marriner, who lived in the beginning of XX century. Biographies and dates of life were found. He mentioned on the site
www.art-searcher.co.uk/Art-Sale/20125--5.html one watercolor (see attachment), written in 1919 (site is outdated, you can only watch from the cache, Google.) Price this watercolor in the "buy now" was little more than five pounds, that is slightly less than 300 rubles. So that your water is apparently written in 1920, and the price ... probably the same;
Igor Guriev right here.
Another was a fairly well-known American artist William Marriner (William Marriner, 1880 - 1914). He is known as one of the founders of the genre "comics", as well as a designer of the first animated film. But he, alas, does not fit: watercolor, he has not worked, and died young - at 1914 (while in the alcoholic delirium, set fire to own house and burned together with the house).