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Comparative Analysis of Storage Capacity in Water Reservoirs of Pao River Basin and Unare River Basin, Venezuela. Cases: Pao-Cachinche, Tamanaco, El Pueblito, El Cigarrón, Vista Alegre, La Becerra, La Estancia

storage capacity,water reservoir,water level

In this research, a comparative analysis is carried out on storage capacity from water reservoirs (WRs) located in Pao River Basin (PRB-V) and Unare River Basin (URB-V), Venezuela. One of the main WRs of PRB-V is Pao-Cachinche Water Reservoir (PC-WR) (179 Mm³). URB is made up of fourteen WRs. Six WR were evaluated in their design useful capacity (DUC), by extracting values from area-water level-capacity curves (AWLCCs). These AWLCCs have been publicly reported by the Environment Ministry. From them, DUCs were calculated obtaining the following results: 1) Tamanaco-WR (T-WR) (1964-1966) (93.07 Mm³), 2) El Cigarrón-WR (EC-WR) (1974-1978) (357.7 Mm³), 3) El Pueblito-WR (EP-WR) (1976-1983) (254.23 Mm³), 4) La Becerra-WR (LB-WR) (1968-1973) (456.49 Mm³), 5) Vista Alegre-WR (VA-WR) (1976-1978) (26.70 Mm³) and 6) La Estancia-WR (LE-WR) (1964-1967) (88.20 Mm³). An approach to bathymetric survey was carried out for 2015. It was implemented by using as equipment consisting a winch coupled with a plumb device with 30 lbs weight and global position system device, to obtain data. For data processing, geographic information system software ArcGIS 10.0 was used to produce WRs terrain elevation maps. Bathymetry was made up of the following control  points separated among them in a mean distance of 200 m, PC-WR (84), T-WR (148), EC-WR (95), EP-WR (91), LB-WR (104), VA-WR (76), LE-WR (136). Bathymetry results indicated that PC-WR has moved its minimum design ground level from 310.00 masl reported in AWLCC for 1961, to 319.90 masl reported in AWLCC for the year 2015, and corresponding to a depth of 38 m in the site of tower-intake hydraulic works. A comparison of bathymetric studies for the years 2001 and 2015 indicated that there was an increase in sedimentation process with an annual rate of sediments 0.143 Mm³ where the space designed to store them was filled, generating a loss of useful capacity in PC-WR of 1 Mm³, representing 0.667% DUC. In URB-V, estimates in volume associated to WRs indicate the following results for sediment volume, useful volume and percentage of lost useful volume, from bathymetric survey in 2015: 1) T-WR (9 Mm³, 84.07 Mm³, 9.67% ), 2) EC-WR (37.2 Mm³, 394.90 Mm³, 10.4%), EP-WR (5.25 Mm³, 259.49 Mm³, 2.07%), 4) LB-WR (157 Mm³, 613.49 Mm³, 3.34%), 5) VA-WR (0.57 Mm³, 26.13 Mm³, 2.07%, 2.13%) and 6) LE-WR (36.16 Mm³, 124.36 Mm³, 41%).  Results obtained showed that T-WR and VA-WR presented sedimentation, while EC-WR, EP-WR, LB-WR and LE-WR showed scour.