Assessment of the accuracy of different standard methods for determining reservoir capacity and sedimentation

Purpose

Determination of reservoir volume has been used in the calculation of sedimentation, hydrodynamic modelling, and dam safety assessment, among others, and the method used as well as its associated error play an important role in the quality of these studies. This study assessed the accuracy of reservoir volume calculations based on different standards for the definition of the spacing between bathymetric range lines. A technique for terrain modelling and a method for determining the survey accuracy are also proposed.

Materials and methods

The reference reservoir volume was based on highly detailed bathymetry (10 m resolution). Seven different spacings were selected, which generated 99 separate bathymetric data sets. For each data set, the volume was calculated based on a digital terrain model according to the usual model (triangular irregular network (TIN)) and according to the insertion of mesh points (IMP) method. This was then compared with the reference volume, and the accuracy of each survey was determined.

Results and discussion

Utilization of a highly detailed and reliable bathymetric survey allowed for the assessment of the associated error in each of the bathymetric data sets, as well as of the spacing standards analyzed. The accuracy of the standards analyzed using TIN modeling ranged from 0.31% to 14.40% (30 and 300 m, respectively). The high errors are attributed to the limitation of the TIN in representing regions near shores, producing incorrect shallow depth readings, resulting in a lower calculated volume than the real volume. IMP modeling exhibited great improvement in performance over the standard TIN (i.e., for 300 m accuracy of 5.51% for IMP and 14.40% for standard TIN), and in none of the cases were the generated volumes greater than the reference volume.

Conclusions

The IMP method proved to be consistent, improving quality of the data while reducing effort in field work. The low accuracies found showed that even surveys following the widely accepted standards contain errors of a magnitude that cannot be ignored. Thus, knowing and evaluating the survey accuracy is of fundamental importance. Definition of standard spacing for reservoirs proved to be unfeasible. This must be defined on a case-to-case basis, considering the error acceptable for the purpose of the survey.     

Fish meal replaced by hydrolysed soybean meal in diets increases growth and improves the antioxidant defense system of silver catfish (Rhamdia quelen)

One of the current challenges of global fish farming is developing plant‐based proteins as a feasible substitute for fishmeal in the formulation of aquafeeds. Substitution levels of fishmeal with hydrolyzed soybean meal (HSM) in diets for silver catfish (Rhamdia quelen) were evaluated for growth, protein metabolism and antioxidant activity. The experiment was carried out in a recirculation system of 20 tanks of 250 L. A total of 300 silver catfish juveniles were used to compose five treatments and four replicates per treatment. Levels of soybean hydrolysate (0%, 5%, 10%, 15% and 20%) were tested in diets (39% protein and 3,500 Kcal) for 60 days. Silver catfish growth was higher at all inclusion levels of HSM when compared to the control diet. No change was shown for body protein deposition. The production of nitrogenous compounds in the liver and muscle was also unaffected by any of the diets. The diet containing 20% HSM promoted an increase in the amounts of non‐protein thiols in the gills and brain. The HSM substitution levels of up to 20% of fishmeal in the diet increases growth and contributes to silver catfish antioxidant activity.