Chronicle: Shawn Coburn farms land that holds senior water rights to the giant Central Valley Project, rights that usually assure him water. Not this year. He already has decided to let his pomegranates die, abandon alfalfa and cut his tomato crop by half. He may not plant any row crops if the state water board follows through on its intention to slash deliveries to "protect human health and safety" from the effects of drought. Coburn, 45, says his ranch near Dos Palos (Merced County) is no water-guzzler....