The practical capacity of a stream will then be determined by its flow at the time when that is least in comparison with the demands of the growing crops. This will be called the critical period, and the volume of water of the critical period will determine the capacity of the stream. The critical period will vary in different parts of the region from the latter part of June until the first part of August. For the purposes of this discussion it was only necessary to determine the flow of the water during the critical period. This has been done by very simple methods. Usually in each case a section of the stream has been selected having the least possible variation of outline and flow. A cross-section of the stream has been measured, and the velocity of flow determined. With these factors the capacity of the streams has been obtained. In some cases single measurements have been made; in others several at different seasons, rarely in different years. The determination of the available volume of the several streams by such methods is necessarily uncertain, especially from the fact that it has not always been possible to gauge the streams exactly at the critical period; and, again, the flow in one season may differ materially from that in another. But as the capacity of a stream should never be rated by its volume in seasons of abundant flow, we have endeavored as far as possible to determine the capacity of the streams in low water years. Altogether the amount of water in the several streams has been determined crudely, and at best the data given must be considered tolerable approximations. In considering the several streams experience may hereafter discover many errors, but as the number of determinations is great, the average may be considered good. METHODS OF DETERMINING THE EXTENT OF IRRIGABLE LAND UNLIMITED BY WATER SUPPLY.