The Ground Is Sinking: California Aqueduct Could Lose 87% of Capacity Without $3.9 Billion in Repairs

The California Aqueduct — the 444-mile canal that delivers State Water Project supplies from Northern California to 27 million people — is sinking into the ground. A January 2026 report from the Department of Water Resources (DWR) puts a price tag on the crisis: $3.9 billion over the next decade to prevent catastrophic capacity loss.

The numbers are stark. Decades of agricultural groundwater overpumping in the San Joaquin Valley have caused irreversible soil compaction — land subsidence — along major stretches of the aqueduct. The canal's concrete liners are buckling and losing capacity.

• 44% of aqueduct capacity has already been lost to subsidence
• Without repairs, reduction could reach 87% within 10 years
• Repair cost: $3.9 billion ($2.96B state / $0.95B federal)
• Scope: raising concrete liners over ~47 miles in pools 17, 18, 20, 21, 24, and 31

Source: DWR — California Aqueduct Subsidence Program

Source: DWR — Subsidence Study Findings (May 2025)

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The Subsidence Problem Undermines the Delta Tunnel Argument

This finding has direct implications for the Delta Conveyance Project (DCP), the proposed $20.1 billion tunnel that would create a new northern intake on the Sacramento River. Tunnel proponents — including the Metropolitan Water District of Southern California and several Bay Area water agencies — argue the tunnel is necessary to protect water deliveries from Delta levee failure.

But the tunnel only addresses the northern end of the delivery system. If the southern conveyance — the California Aqueduct itself — cannot carry the water due to subsidence, a new northern intake is functionally useless.

As the Santa Barbara Water Commission noted in a February 2026 warning: the aqueduct capacity crisis is the more immediate threat to statewide water delivery than Delta levee vulnerability.

Source: edhat — Santa Barbara Water Commission Warning (Feb 2026)

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Legislative Response: SB 872

In March 2026, California legislators introduced SB 872, which would allocate $300 million per year for 20 years ($6 billion total) from the greenhouse gas reduction fund — half for Delta levee improvements and habitat restoration, half for repairing subsidence damage along the California Aqueduct.

The bill attracted an unusually broad coalition: Restore the Delta, the State Water Contractors Association, the Delta Counties Coalition, Sierra Club, Defenders of Wildlife, and even the Metropolitan Water District.

On March 18, 2026, California legislators and stakeholders held a joint session to address the aqueduct crisis, signaling bipartisan urgency.

Source: Contra Costa News — Legislators Unite to Protect Water (Mar 18, 2026)

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Root Cause: Groundwater Overpumping

The subsidence is caused by decades of agricultural groundwater extraction in the San Joaquin Valley — the same region that consumes a significant share of California's total water supply. When water is pumped faster than it recharges, the clay layers in aquifer systems compact permanently. The ground surface drops. Infrastructure built on that ground — canals, roads, pipelines — deforms.

The USGS has documented subsidence along the aqueduct since the 1920s, but the rate accelerated during the 2012-2016 drought when surface water allocations dropped and farmers turned to wells. California's Sustainable Groundwater Management Act (SGMA), enacted in 2014, is designed to bring basins into balance by 2040 — but the aqueduct damage is already done.

Source: USGS — California Aqueduct Subsidence

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The Math

The Delta Conveyance Project costs an estimated $20.1 billion and would take 15-20 years to build. California Aqueduct subsidence repairs cost $3.9 billion and can begin immediately. Comprehensive Delta levee upgrades cost $3-12.5 billion depending on scope. Combined aqueduct and levee repairs protect both the delivery system and Delta communities, infrastructure, and ecosystems.

The policy question is whether California ratepayers should spend $20 billion on a new northern intake while the southern conveyance system collapses underneath them.

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This article aggregates reporting from DWR, USGS, Contra Costa News, and edhat Santa Barbara. dMedia did not conduct original reporting for this piece.