The Balsa Inferior Hydroelectric project consists of a 4 km tunnel that will take water from the Rio Balsa through the tunnel down to a series of turbines and then returns to the river. The project will be a 45 megawatt facility when completed.
Total sediment volume is up to 30 times larger than the original design specification due to high wet weather conditions. Dewatering flow rates are ten times larger than the original design and the sediment loading rate is at a two-times to three-times increase over the original design. In addition, the available treatment train footprint is severely limited to make retrofits, thus a goal of 80% removal of suspended solids was set. Setting a specific turbidity limitation was not viable given the footprint available.
HaloKlear designed a semi-passive lined treatment channel incorporating excelsior matting and wattles – the DPS material is deployed on the matting. Modifications were made to the channel by adding a deep settling area at the end of the channel to add more sediment capacity, and the DPS was inserted into segmented refillable socks that are deployed in corrugated pipes on the inlet to the treatment channels. A second wattle channel was added of similar design and a corrugated pipe deployment was added to the existing concrete settling chambers. The three treatment systems each receive only an average of 500 gpm (30 L/s) allowing them to be able to deliver significant reduction.
Currently, the sediment load is being reduced by 60 to 70%. An 80%+ sediment load reduction will be attainable with final modifications in how and when site personnel clean and maintain the treatment systems. Once the modifications have been complete, the treatment system will prevent 30 to 35 m3 of sediment from entering the Balsa River daily.