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Debris and alluvial fans are composed of clay, sand, gravel, cobble boulders, and other debris deposited at the foot of a steep channel where the channel gradient lessens, flow spreads on the fan, and flow velocity is decreased sufficiently to cause such deposits. These deposits are fan shaped and have relatively undersized channels. The channels generally are dis- continuous and are subject to sudden relocation across the fan during runoff. Cross-sectional relief is relatively small and may slope away for some distance on either side of the sides of the channel. Gol'din and Lyubashevskiy (1966), Dawdy (1979), and Magura and Wood (1980) present alternative hydraulic methods to analyze the hazards for debris flows and debris and alluvial fans. Except for sand-bed streams, the channel bottom is not uniform but is a series of steps or drops whose spacing and height are controlled by the slope (Judd and Petersen, 1969). As slope increases, spacing decreases and height increases. These steps develop as deposits of boulders across the channellike drop structures or as natural bedrock outcrops; these steps have been noticed on most high-gradient boulder-bed streams. Extreme care needs to be taken in making hydraulic calculations that span one or more of these steps because the flow usually passes through critical depth. Cross sections need to be placed immediately upstream and downstream from a critical depth control. High flows may drown out these steps. Minimal verification exists in hydraulic computations beyond slopes of 0.05 in natural streams (Barnes, 1967). When stream slope exceeds 0.05, hydraulic computations may be inaccurate. The passage of a flood can cause dramatic changes in channel geometry and roughness in a very short time. Contracting reaches are susceptible to scour at high-flow velocities, whereas deposition can occur in either contracting, uniform, or expanding channels. Although scour is a function of a number of flow, channel, and soil properties, the most dominant factor seems to be stream slope. As slope increases, particularly in excess of 0.03 to 0.04, scour increases greatly. In many high-gradient streams, almost their entire length can be scoured or filled. This is not meant to imply that erosion and channel enlargement cannot occur on flatter slope streams. A check for past flood erosion and depositional features needs to be made for all hydraulic computations. CROSS SECTIONS Location Prior to the selection of the roughness coefficient values, an office study and an onsite investigation need to be made to properly locate the cross sections that would be used in the hydraulic analysis (Benson and Dalrymple, 1967; and Davidian, 1984). If low-level aerial photographs and detailed topographic maps or both are available, cross sections and study reaches need to be placed on them and then their location checked onsite. 5