4.1.1. Particle Size

The analysis showed that 99.58% of the particles at the desilting basin were finer than 425 μm. In addition, the largest percentage (62.33%) of particles was finer than 75 μm. Figure 7 shows the particle size distribution of the sediment samples. The median grain size was determined as 9.28 μm. Furthermore, the characterization of the particle density was performed, obtaining a value of 2650 kg/m3.

**Figure 7.** Sediment size distribution.

#### 4.1.2. Mineral Composition

Figure 8 shows the proportion of the mineral content in sediment samples. The results showed that plagioclase minerals represented the highest proportion of sediments in the samples. The hardness values for this mineral group lies between 6.5 and 7.5 in the Mohs scale. When comparing this mineral composition to other reports, a difference in the proportion of quartz and plagioclase sediments was observed. Quartz is typically the predominant mineral found in most rivers, while in this study, plagioclase minerals composed the greatest part of the sediments found in Pastaza River. Nevertheless, the hardness values did not seem to differ significantly from other studies [10–12,14].

**Figure 8.** Sediment mineral composition.

#### 4.1.3. Particle Shape

Figure 9 presents the shape of the sediments found in the samples. The analysis exhibited the sharp and slightly rounded edges of the sample particles, which are equivalent to angular and subangular particles based on IEC 62364 standards [33].

**Figure 9.** Shape of sediments found in Pastaza River.

Comparing the shape of the sediments with the sample chart, the sphericity and roundness were found to be *S* = 0.7 and *R* = 0.3, respectively.

#### 4.1.4. Sediment Concentration

Table 6 shows particle concentration values in the river under normal conditions. The average concentration value was used to determine the particle mass flow rate.

**Table 6.** Particle concentration in Pastaza River (kg m<sup>−</sup>3).


#### *4.2. Flow Field Prediction*

Since erosion is governed by the velocity, incidence angle, and concentration of the solid particles at the time of collision, the erosion prediction depends on the solutions of these parameters. Figure 10 presents the flow field in the turbine, where the main parameters that influence the sediment flow field are the inlet flow and the guide vane opening. In this context, the highest velocity of the flow was observed on the pressure side near the leading edge for the stay vanes. On the other hand, guide vanes and runner blades presented higher flow velocity on the suction side and trailing edge

The efficiency of the turbine was calculated at four different operating points using the data from the flow numerical solution. These results were compared with the experimental data from SFH, as shown in Figure 11.

Satisfactory agreement between results was obtained, though a better prediction of the efficiency was obtained for higher flow rates.

**Figure 10.** Velocity distribution in flow components at the best efficiency point.

**Figure 11.** Numerical and experimental efficiency of the turbine.
