Chira-Piura Water Management System, Peru

Approval was given in June 2002 for the building of the 15.4MW Poechos hydroelectric plant in Peru. It is envisaged that this will be the start of the final phase in a thirty plus year programme to construct the Chira-Piurra water management system.

The purpose of the Multipurpose Water Management System has been to improve the accumulation of water stocks in the upper part of Peru's Chira basin by introducing flood controls, irrigation, drainage and electricity production.

LOCATION - NORTHERN PERU

The Chira-Piura Water Management System is situated in the northern most part of Peru, in the lower flow of the rivers Chira and Piura, which run into the Pacific Ocean. The Poechos Hydroelectric Project is to be constructed on the Poechos irrigation dam located in the district of Piura part of the northern Peruvian province of Sullana, approximately 30km from the border with Ecuador.

ENGINEERING DESIGN

The design brief was to revitalise the Piura valley, which was short of water, and provide modern irrigation for approximately 35,000ha of arable land.

A multi-national team of engineers carried out the overall design of the water management system. It comprised Energoprojekt - Hidroinzenjering from Yugoslavia, USA-based IECO, local companies LAGESA and Novoa from Peru along with German company, Salzgitter.

The engineering solution was based on accumulating water surplus from the upper part of the Chira basin into the Poechos Irrigation Dam, and transporting part of this accumulation into the Piura basin by means of a headwater channel 55m long.

In parallel, new irrigation and drainage systems were installed throughout the 35,000ha of arable land within the Lower Chira basin.

Next to the main channels, two headwater dams were built along the regulated river flow of both rivers and the channel network for irrigation and drainage of the reclaimed ground.

The Curunuy dam and power plant, completed in 2000, is located at the outflow chute of the headwater channel in the Chira valley. The other was the Poechos dam, completed in 1977. This is where the recently approved hydro plant will be constructed.

SYSTEM CONSTRUCTION

The system was built in phases: Phase one from 1970 to 1977; phase two from 1978 to 1985; phase three from 1985 to 1997 and the final phase is expected to begin by the end of 2002.

Based in Belgrade, Yuogslavia, Energoprojekt has been the main contractor throughout the water management system project. Its Peru-based company, Energoprojekt - Izgradnja has worked alongside a consortium of Peruvian companies comprising GOSA, Metalna, COSAPI, UPCA and VILLASOLI.

The first phase - from 1970 to 1977 - included the rock filled Poechos dam (9km long with a maximum height of about 55m and a total excavation volume of 9,000,000m³; the diversion tunnel built into the bottom outlet with a maximum capacity of 14m³/s; the concrete gravitational block of the overflow structure (400,000m³ concrete) with radial gates with a total capacity up to 5,500m³/s and the safety overflow of approx. 200m long with a capacity up to 10,000m³/s. The headwater discharge and the headwater channel have a capacity of 70m³/s (8,00,000m³ excavation and 1,000,000m³ of concrete for channel lining) and the channel drainage system in the lower Chira (10,000,000m³ excavation in total) flows through over 1,000 structures on the channel network (overflows, outlets, gates, etc.)

The second phase - from 1977 to 1985 - covered the headwater dam, Los Ejedos, which is 220m long with a maximum height of 20m and a gate capacity of 3,000m³/s; the main channel, which is 42km long and has a capacity of 45m³/s; the protecting embankments (60km long) along the Piura; and the channel system with supporting structures over an area of 35,000ha.

The third phase - from 1985 to 1996/7 - consisted of the headwater dam, Sullana, which is 75m long, has a maximum height of 12 m and has gates with a total capacity of up to 5,000m³/s, the headwater channel, Norte, with a capacity of 25,500m³/s over 56km which irrigate 15,000ha, the channel, Sur, which is approx. 35km long with a capacity of 7m³/s for irrigation of about 7,000ha (in total about 5,000,000m³ excavation), and about 60km of dykes along the regulated river bed in the lower Chira flow (about 5,500,000m³ of embankment).

The final phase, from 1997, includes the Curunuy dam and power plant, completed in 2000, and the 15.4MW Poechos Hydroelectric Project, which was approved in June 2002 and will take an estimated five years.

POECHOS HYDROELECTRIC PROJECT

The Poechos Dam will operate using drainage catchment from the Chira river basin system that extends northwards into Ecuador. The energy potential of the Chira-Piura irrigation system has only been considered as a secondary benefit and to date has only been partially used through the installation of the Curumuy hydro plant that generated about 65GWh in 2000.

The Curumuy plant, which is owned by Sindicato Energético, S.A, was completed in 2000 and uses the drop in elevation between the watersheds of the Chira and Piura river systems.

The design of the Poechos project is largely based on the passive utilization of water flows dependent on irrigation demand. During months of lower irrigation demand, however, it will be possible to generate additional energy by using a small existing reservoir that serves as a regulating reservoir located at Sullana about 40km downstream from Poechos on the Chira River.

POECHOS RESERVOIR

The inundated area of the Poechos reservoir covers about 70km² and will not be increased as a result of the project. No roads will be constructed as a result of the project since it utilizes the existing roads to the Poechos dam. Similarly, the transmission line will have minimal impact since most of it will follow an existing right-of-way of a road or canal. In the exceptional cases, rights of way will be negotiated with the private owners within the framework of the electrical distribution laws that provide for equitable treatment in the accession of rights of way.

The project will take 45m³/s of water from the Poechos dam.

The plant will rely on flows of water dictated by irrigation demands and, as such, is expected to generate about 70GWh of electrical energy per year.

POWER PLANT

The power plant project will consist of the following components: a steel penstock connected to an existing steel discharge pipe at the base of the dam; a powerhouse equipped with two Kaplan turbines which drive two 9.5MVA generators; a switchyard located near to the powerhouse; and a 35km long overhead transmission line from the switchyard to the Sullana substation of the national electrical grid.

After exiting the generators, the water will be discharged into the pre-project, energy dissipater of the Poechos dam and fed into the irrigation system. The energy to be produced by the Poechos Hydroelectric Project will be sold to Electronoroeste, S.A., the concessionary for energy distribution in northwestern Peru, under a Power Purchase Agreement. The total cost of the project is nearly US$16.3 million.