PRECISION OF CHANNEL WIDTH AND POOL AREA MEASUREMENTS

The precision of width and pool area measurements has rarely been cons idered in relation to downstream or at section hydraulic geometry, fis heries studies, long-term or along a continuum research studies, or ag ency monitoring techniques. We assessed this precision and related it to other stream morphologic characteristics. Confidence limits (95 per cent) around mean estimates with four transects (cross-sections perpen dicular to the channel centerline) ranged from +/- 0.4 to 1.8 m on str eams with a width of only 2.2 m. To avoid autocorrelation, transects s hould be spaced about three channel widths apart. To avoid stochastic inhomogeneity, reach length should be about 30 channel widths or ten t ransects to optimize sampling efficiency. Precision of width measureme nts decreased with decreased depth and increased with stream size. Bot h observations reflect variability caused by features such as boulders or coarse woody debris. Pool area precision increased with pool area reflecting increased precision for flat, wide streams with regular poo l-rime sequences. The least precision occurred on small, steep streams with random, boulder or coarse woody debris formed pools.