Here's one that that would refill Lake Chad using water diverted from a nearby river and pumped 128km up 180m to enter the Lake Chad basin.
Ubangi – Lake Chad Water Transfer Using Solar Option
A. Sample Project Specifications for the Solar Option
[N.B. cost estimates are in $US dollars.]
Intakes and Pumps: Four submerged intakes on the Ubangi River will supply the pumps and pipeline. The intakes will not require a dam and will screen for fish. Four independent pumping stations located on the north shore of the Ubangi in the CAR (above high river flow) will supply water to each of the four pipelines.
Pipelines: Four parallel conduits, 5 meters in diameter each, will convey water uphill from the Congo River Basin to the Lake Chad Basin. The IBWT pipelines will be 128 km in length and raise water 180 meters to the inter-basin crest.
Canals: Once the water is elevated to the inter-basin crest of the Lake Chad Basin, it will flow approximately 1000 km by gravity in natural waterways and improved canals to the Chari River, and thence to Lake Chad.
Solar Power: Recent cost reductions for silicon PV panels to less than $0.30/W (2) make solar power a viable replacement for hydroelectric power. Large arrays of solar panels (near the pumping site on the Ubangi River) will supply the power needed to pump a volume of 100 m3/s during 8 daylight hours (the daily period of intense sunshine).
Battery Pumping: Projected cost reductions for grid-scale lithium-ion batteries (3) to $100/kWh allow for nighttime pumping for 16 hours per day. Initially, only 1 of 4 of conduits will be pumped by battery power after sunset, giving 24 hours per day flow at 25 m3/s. Continuous pumping will keep water flowing at all times in canals and rivers to Lake Chad, assuring a minimum steady supply.
Cost of Solar Option: Installation of 375MW of solar panels will cost $135M. Installation of lithium-ion 1000MWh grid-scale battery will cost $130M. Total cost of Solar Option solar panels and a single grid-scale battery will be $267M (less than 10% of the cost of the hydroelectric dam).
Impact on Rivers: A volume of 100 m3/s of water pumped to Lake Chad will use 0.7% to 5% of the Ubangi River flow (4). Water pumped to Lake Chad is about 0.25% of average Congo River discharge to ocean (5). These rates of water transfer to Lake Chad are unlikely to affect the ecology or navigability of the Ubangi River. IBWT will not impact the planned Grand Inga hydroelectric development on the Congo River in the DRC. The pumped output of the Solar Option could double the Chari River flow to Lake Chad in April and May (6), during low water years.
Staged Construction: Unlike the hydroelectric dam, the Solar Option allows for staged construction and earlier pumping than from a dam. Shown below are the incremental approximate costs for each stage.
- Stage 1. One 5 m pipe; (8hr); requires 63MW solar; cost: $23M
- Stage 2. One 5 m pipe; (24hr); add 125MW solar + 1000MWh battery; cost: $175M
- Stage 3. Two 5 m pipes; (8hr & 24hr); add 63MW solar; cost: $23M
- Stage 4. Three 5 m pipes; (8hr, 8hr & 24hr); add 63MW solar; cost: $23M
- Stage 5. Four 5 m pipes; (8hr, 8hr, 8hr & 24hr); add 63MW solar; cost $23M
The total cumulative cost is $267M for the Solar Option. [NB: This cost estimate for the Solar Option does not include water intakes, pumps, pipelines, canals or new roads.]
Time to Fill Lake Chad: The completed Solar Option will pump 1.58 billion m3/year to Lake Chad (50% of the rate of the hydroelectric dam). Based on the CIMA Feasibility Study, solar pumping will raise Lake Chad by 50 cm and increase area by 3000 km2 in 1 year. It may take 2 to 5 years to restore the Lake Chad fishery, depending on competing domestic and irrigation water consumption, as well as water loss from evaporation.