Quebrada de Ullum Dam and Hydropower Plant

The Quebrada de Ullúm Hydropower Plant is located on the San Juan river, about 20 Km away from the city of San Juan. Access is gained by means of Provincial Highway 60, which connects San Juan to Ullum.

The hydroelectric complex consists of a stop over the main part of the Río San Juan river, made by means of a rockfill dam, which is then followed by an ungated spillway. This sector is made up of the headrace tunnel, internal pressure pipes, power house, and the 132 kV playa.

Flow through the generator is controlled by the outlays controlled at the Ullum reservoir, with the end being to satisfy the water demand generated by the Valle de Tulum valley. The Kaplan turbine is able to handle a wide range of flow, from 21 m³/sec up to 105 m³/sec, if permitted by the proper amount of precipitation.
The limitation in production stems from the need to irrigate, which is why this was designed as a run-of-river project.

Description of the plant and nearby structures:

Penstock: this recess into rock has a length of approximately 155 meters at 5 meters of diameter, starting from the fork to irrigation.
Well and valve chamber: this upward, circular excavation 45 meters deep into the rock is covered in concrete to have an internal diameter of 7.4 meters. The valve chamber is an expansion of the well at its lowest point; it is 19 meters high and has a diameter of 12 meters.
Throttle-body sensor: It is biplane with 5 meters in diameter. The operating pressure is at 4.84 kg/cm² and nominal flow is 118 m³/sec.
Power house: It is enclosed and has space for the fitting and roof of the nave, with dimensions of 18 m wide, 46.4 m long, and 31 m tall (not including the columns of the bridge crane outside) and is made up of 4 floors or levels.
Generator: It is of synchronous alternating current at 50,000 KVA, 13200 V, and 2187 Amp; It is at 50 Hz with a power factor of 0.8.
Turbine: It is a Kaplan turbine with a nominal power of 42300 KVA giving a net head of 44 meters and a flow of 105 m³//s, and a velocity of 176.5 rpm.
Bridge crane: It is external and consists of two wenches, a main one at 275 tons, and another at 30 tons. Their hoistings reach 31 meters and 36.5 meters, respectively.
Transformer station: Located to the left of the plant, it has only one switching position and tension at 132 kV. It is a TATBA transformer with 50 MVA of nominal power.

Description of the dam:

- It is located in the Quebrada de Ullum gorge, over the San Juan river, approximately 20 km northeast of the city of San Juan.
-The dam, finished in December of 1980, is made of loose, graded materials and has a crowning length of 350 meters and a height of 67 meters from its foundations, which are comprised of three main elements: an impermeable inner core, filters, and shoulders. A layer of riprap protects the upstream face from erosion caused by waves in the reservoir.
-Reservoir capacity: The San Juan river was studied for 60 years in order to determine the optimal capacity for the reservoir in order to produce the highest economic benefit for the Valle de Tulum valley. The figures obtained are the following:

-Flow of the river is 60 m³/s
-Maximum volume at the height of the spillway (cota 768 m.s.n.m) 440 Hm³
-Minimual operational volume (cota 745 m.s.n.m) 49 Hm³
-Usable volumen of the reservoir 391 Hm³
-Maximum area (cota 768 m.s.n.m) 3100 Ha

Overflow channel: Built into a deeply excavated area on the left bank, with an ungated side-channel spillway, a spillway basin, a chute, and an energy dissipater, it is designed for a maximum flow of 2560 m³/s. The overflow channel passes through two bridges made of prestressed concrete, one located at the crest (elevation 777) and the other at elevation marker 725.5 over the auxiliary access road going to the hydroplant.

Sluices: A—a sluiceway with a load-bearing base at elevation marker 751, which unloads into the spillway basin and is gated for higher control. B—a sluiceway that consists of a 5 meter-in-diameter tunnel run through with a 3.7 meter-in-diameter pipe that unloads in the spillway. Control is maintained by way of a gate at the threshold of the intake, located at elevation marker 725. C—the diversion of water for irrigation and hydroplant use is done via a tunnel that is 6 meters in diameter, with a further offshoot with a 5-meter-diameter pipe going to the valve area, and another going to the scour outlet valves.

The Hydroelectric plant and the toe of the dam is connected via a high-tension line that runs to the Maniobras Punta de Rieles substation. This line is made of concrete posts and metal towers that transport 132 kV by means of 3 conducting cables and their respective guard cable.

Beginning in September 2004 and lasting until 2034, EPSE is and will be the provincial caretaker for the exploitation, operation, commercialization, and maintenence of the Quebrada de Ullum Hydroplant.

Some of the benefits that came along with the construction this dam can be described as follows:
-Regulation of the San Juan river, guaranteeing irrigation for all of the San Juan oasis (main goal of the project).
-Following the installation of the hydroplant, an energy output of 17.2 million kV/hour/year (172 GWh/year).
-Improvement in drinking water quality for the population, as the reservoir serves as a decanter for suspended material brought by the river before the water continues to the water treatment plant in Marquesado, which reduces the cost of filtration.
-The Quebrada de Ullum Dam has greatly changed tourism in our province, with tourist complexes now dotting the lakefront that have become grand centers for sought after recreational activities.