San Clemente Dam Decommissioning: River Restoration & Engineering Design

The removal of the Elwha River dams in Washington State demonstrates that dam removal can rapidly restore ecosystem function, with over 65% of accumulated sediment (more than 20 million cubic meters) being mobilized and redistributed, leading to significant increases in native fish populations (Chinook and steelhead) and recovery of riparian and estuarine habitats within just a few years of dam removal.

Dam removal initiates cascading ecological improvements requiring comprehensive post-removal monitoring. Projects implement multi-year monitoring programs including drone flights (three times annually for three years) to track channel evolution, fish population sampling to assess species distribution changes, and vegetation monitoring to prevent invasive spread into upstream areas. The ecological differences between free-flowing rivers (narrow channels, continuous flushing, high DO) and impounded reservoirs (stagnant conditions, eutrophic tendencies, dangerous diel oxygen cycles) become apparent as natural processes resume. Long-term assessment demonstrates how dam removal restores natural river functions that had been suppressed for decades.

Dam removal initiates a multi-year ecological recovery process with distinct phases. Immediate improvements include elimination of oxygen stratification, restoration of natural flow patterns, and improvement of dissolved oxygen and temperature conditions. Aquatic insect recovery occurs relatively quickly because adults can fly to newly accessible habitats. Fish population recovery takes longer as fish must migrate to utilize restored habitats. Historical data from previous dam removals demonstrates that these recovery processes are predictable and successful, validating the investment in dam removal projects for long-term ecosystem health.

Successful dam removal and ecosystem restoration requires coordinated multi-stakeholder partnerships involving Indigenous nations, conservation organizations, watershed associations, municipalities, and federal agencies. The Campbell Creek project demonstrates how diverse partners can collaborate to secure funding, conduct baseline monitoring through methods like electrofishing and eDNA sampling, develop management plans, and execute decommissioning while preserving archaeological resources. Post-removal efforts include planting native species to restore riparian zones and implementing long-term monitoring to track recovery. This collaborative approach recognizes that dam removal marks the end of an era of obstruction and the beginning of restoring free-flowing streams that supported ecosystems and Indigenous communities for thousands of years.

Effective riparian restoration requires systematic monitoring frameworks guiding adaptive management decisions over decades. Active restoration techniques include sourcing ecotype-specific native plants, auguring holes to reach water tables for irrigation-free establishment, and developing cottonwood pole plantations for efficient water table planting. Monitoring programs combine short-term annual assessments to guide next-year work plans with long-term evaluations of ecosystem recovery. A Dolores River cottonwood study revealed survival correlates with salinity at planting hole bottoms, informing site selection criteria. Geomorphic monitoring comparing erosion rates before and after tamarisk removal showed cleared sites experienced 2.2 meters/year erosion versus 1.4 meters/year for uncleared sites, demonstrating how invasive removal affects channel stability differently based on flow regime characteristics. Long-term outlooks project continued tamarisk beetle expansion into Arizona, Texas, and Mexico, with effects varying by ecosystem—where native plants exist, beetles enable recovery; where invasive weeds dominate, additional management is needed.

The Elwha River, located on the Olympic Peninsula in Washington state, was historically one of the few rivers in the United States supporting all anadromous salmonoid species native to the Pacific Northwest. The river supported 11 varieties of salmon and trout spawning in its cold clear waters. Salmon serve as keystone species, holding entire ecosystems together with over 130 species depending on them—from bears and eagles in forests to orcas and humpback whales in the Pacific Ocean. Salmon transport energy and nutrients between ocean and freshwater environments, picking up carbon and nitrogen at sea and distributing these nutrients throughout forest ecosystems when consumed by predators. Between 1913 and 1926, the Olympic Power Company constructed two dams that formed complete barriers to salmon migration, degraded the watershed, and caused the loss of 90% of salmon habitat, resulting in a 98% decline in fish populations.

The Elwha Dam removal (begun in 2011) is the largest dam removal project in history and one of the biggest river rehabilitation success stories. It opened important salmon habitat, restored vegetation, and allowed wildlife to return to the landscape where reservoirs once existed.

The Klamath River, California's second-largest river, hosted four major dams built between 1918 and 1964 at $400 million, generating 169 MW for 70,000 homes. These dams—JC Boyle (embankment, 68 ft), Copco 1 (concrete arch), Copco 2 (gravity, 33 ft), and Iron Gate (tallest)—transformed the ecosystem, blocking salmon migration and causing over 90% population decline. Indigenous tribes suffered for over a century. After failed mitigation attempts ($450 million fish ladder proposal), regulatory pressure led to removal. A landmark agreement split costs: Pacificorp ($200M via surcharges), California ($50M), Oregon ($15M). Demolition required years of planning, sediment testing, fish relocation, and phased demolition. Native seed collection from 98 species began restoration. Scientists project 86% salmon recovery by 2061. This case illustrates how environmental restoration requires multi-stakeholder collaboration, balancing economic trade-offs against long-term ecological benefits.

The Klamath River dam removal project in California represents the world's largest dam removal effort, involving the demolition of four hydroelectric dams that blocked salmon migration for over a century; this $450 million project, completed in 2024, restores approximately 400 miles of salmon habitat and serves as a blueprint for river restoration nationwide, demonstrating how decades of environmental activism by indigenous tribes and environmentalists can overcome economic and regulatory obstacles to achieve ecosystem recovery.

Removing dams can restore river ecosystems and trigger a chain reaction of ecological recovery, as demonstrated by the Elwha River in Washington State where salmon populations have rebounded and marine-derived nutrients are enriching surrounding forests, showing that nature can heal when given the opportunity.

Water infrastructure community impact resolution requires: (1) understanding hydrological patterns, (2) balancing competing interests, (3) establishing appropriate remedies, and (4) community participation in resolution. The Volcán water infrastructure case required: (1) understanding hydrological patterns, (2) balancing competing interests between municipal infrastructure and private property, (3) establishing appropriate remedies, and (4) community participation in resolution processes. Water infrastructure planning requires: (1) community participation in planning, (2) technical assessment of needs, (3) consideration of community capacity, and (4) phased implementation. The process requires: (1) understanding applicable laws, (2) balancing competing interests between municipal infrastructure and private property, (3) establishing appropriate remedies, and (4) community participation in resolution processes.

Water supply infrastructure planning involves multiple stakeholders and requires community participation. The mayor explained that for villages like Serentani and Diaselo, the municipality has developed two proposed solutions: (1) Integrating existing water infrastructure, (2) Developing new water sources. The process includes: (1) Gathering community input and signatures, (2) Technical analysis by municipal services, (3) Cost estimation and feasibility assessment, (4) Considering alternative solutions including cultivation of existing water sources. The most economical solution is preferred when possible, but technical and financial constraints may require more expensive alternatives.

Water infrastructure development involves trade-offs: (1) Reservoirs provide water storage but convert agricultural land to water surface, (2) Pumping from groundwater can deplete aquifers, (3) Multi-purpose infrastructure serves multiple needs but may be less efficient than single-purpose solutions. Economic analysis should capture these trade-offs to inform decision-making.

Water utility infrastructure requires security: treatment plants are critical infrastructure, security concerns include malevolent acts, natural disasters, and cyber threats, and redundancy and reliability are important. Water treatment capacity planning involves: current plant capacity may need expansion, redundancy ensures continued service during emergencies, older plants may need replacement, and the goal is to ensure adequate capacity and reliability for the community. Property acquisition involves: negotiation with property owners, price determination, appropriation ordinance presentation, and council consideration and approval. The goal is to acquire property for public benefit while following proper procedures.

Water infrastructure decisions follow processes: (1) Technical assessment, (2) Regulatory review, (3) Stakeholder consultation, (4) Implementation planning. Decision-making processes ensure infrastructure investments are justified and properly executed.