Table 21. Estimation of length of hypothetical M1 water surface profile (backwater) upstream of Amolar and Porto da Manga.1 Station Property Units Amolar Porto da Manga Mean annual discharge m3/s 943 1340 Bottom width, estimated 2 m 300 300 Side slope, estimated m 1:1 1:1 Channel slope 3 cm/km 1.82 2.06 Channel slope m/m 0.0000182 0.0000206 Manning friction coefficient n 4 - 0.015 0.02 Normal depth (yn) m 4.296 6.113 Downstream depth increase (Dy) 5 m 0.470 0.440 Downstream depth (yn + Dy) m 4.766 6.553 Amolar       Distance to Porto Conceição 6 km 216 - Length of M1 profile (95 % of Dy) km 225 - Distance to Descalvados 6 km 337 - Length of M1 profile (99 % of Dy) km 339 - Distance to Cáceres 6 km 476 - Porto da Manga       Distance to Amolar 6 km - 280 Length of M1 profile (95 % of Dy) km - 280 Distance to Bela Vista do Norte 6 km - 361 Length of M1 profile (99 % of Dy) km - 417 Distance to Porto Conceição 6 km - 496 1 Based on direct step method, assuming a prismatic channel and a 0.001 m depth interval (Chow, 1959). 2 From Table 1. 3 From Table 12. 4 Average measured value, based on streamflow data from DNOS (1974), DNAEE, and Hidrologia S. A. 5 Taken from Section 3.3.1. 6 Distance measured along the river.