The relationship between water-surface slope and 12 hydraulic variables was examined for a reach scale and a more local scale, using data from 12 reaches. Measurements of width, depth, velocity, slope, and roughness elements were made on 12 reaches of gravel-bed streams at bankfull stage. All of the reaches have fairly well-developed riffle-pool sequences and are either straight or braided in channel pattern. Measurements were made at numerous locations within each reach so that the influence of hydraulic and resistance variables on water-surface slope could be examined both within and among reaches. Results show that roughness elements and resistance coefficients correlate most highly with water-surface slope. Bed particle size correlates well with water-surface slope at both reach and local scales. The magnitude of bed undulations correlates well with slope at the scale of a reach. In the type of stream channels examined, the important components of resistance in the channels are also the most important influences on water-surface slope.