Ensuring abundant groundwater in California for years to come

A landmark groundwater sustainability plan will provide a clear criterion for sustainably maintaining the Eel River Valley Groundwater Basin for the next 100 years.

Eel River is California’s third largest instate watershed, covering 3,684 square miles, and crucial to Humboldt County communities and local wildlife. The watershed recharges a significant coastal groundwater basin that supplies groundwater for agriculture production as well as general household, industrial and business use.

When the basin was designated as medium-priority by the California Department of Water Resources under the Sustainable Groundwater Act (SGMA), the Humboldt County Groundwater Sustainability Agency (GSA) engaged GHD to gather a diverse group of scientists to develop decision making guidelines and an initial outline of management activities that ensured high quality and abundant groundwater resources indefinitely.

Before developing recommendations for the Eel River Groundwater Basin Sustainability Plan, GHD undertook multiple studies to understand how ecology and industry relied on the river. The figure above maps the distribution of various aquatic species throughout Eel River.

To better understand the pumping thresholds of each well, GHD figured the percent of pumping above the well’s baseline required to impact the associated Maintenance Easement (ME) area. As a proxy measurement, GHD provided the client with groundwater elevation minimum thresholds, which can also be used to monitor extraction thresholds and prevent impacts to the ME areas.

To develop the plan, the team collected data and performed a detailed analysis to characterize the groundwater basin, including interactions with surface waters, saltwater intrusion, land subsidence, and estimate the fluctuating groundwater in storage over the last 20+ years.

The data was then used to construct a basin-wide surface water coupled to groundwater numerical model. With that information, we developed reliable estimates of surface water and groundwater budgets. This modelling has enabled the Humboldt County GSA to continually monitor the effects of groundwater pumping, proactively plan for the threats posed by climate change and iteratively adjust their management activities accordingly.

The strategic advice provided by GHD will help our client sustainably manage high quality and abundant groundwater resources for all stakeholders, providing for human consumption, agricultural irrigation, and environmental services.

In providing Integrated Water Management (IWM) services on such projects as this, GHD is helping clients develop sustainable long-term plans for water cycle services and secure a diversified, sustainable and resilient water future.