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Trout Unlimited outlines coastal hydrology monitoring and a regional drought forecast for riffle-crest depth and summer flow
Summary
Trout Unlimited described its 108-site stream-gauge network, paired groundwater monitoring, project examples showing how storage/forbearance improved summer flows, and a planned regional drought-forecast tool using LSTM streamflow models and a random-forest riffle-crest-depth predictor to inform seasonal management and instream-flow standards.
Mia Van Doto, California Water Program Director at Trout Unlimited, presented the conservation hydrology program's monitoring network and a forthcoming forecasting tool designed to predict summer streamflow recession and riffle-crest depth (RCT), an ecological indicator tied to pool connectivity and juvenile salmon survival.
Trout Unlimited maintains 108 active stream gauges across coastal and tributary streams and monitors groundwater at roughly 84 wells, often pairing gauges and wells to understand surface-groundwater interactions. Van Doto described two restoration and water-conservation projects where storage, forbearance and flow releases materially changed summer hydrographs: a Dutch Bill Creek project that eliminated nightly diversion drawdowns from a camp and a Green Valley Creek project where spring storage and forbearance altered hydrograph slope favorably for rearing habitat.
On modeling, Van Doto said the coalition is developing a two-part regional drought tool: a long short-term memory (LSTM) network for streamflow forecasts and a random-forest model that uses lidar-derived attributes and rating curves to predict riffle-crest depth and the timing of pool disconnection. "Summer stream flow is always going to be low in these coastal tributary watersheds," she said, "and we really need streamflow standards to protect summer stream flow in the long term because they're highly sensitive to water extraction." The tool will initially cover the Central Coast coho range and the South Fork Eel watershed; phase two includes a dashboard and operational analyses to indicate when management actions are needed.
Why it matters: Riffle-crest disconnects correspond to pool isolation and elevated juvenile mortality risk. Van Doto cited research linking duration of pool disconnection to survival rates in coho and other species. The forecast tool aims to give managers an early warning of when critical thresholds are likely to be crossed so that targeted actions (flow releases, forbearance, diversion management) can be planned.
Trout Unlimited invited partnerships with counties and landowners to expand gauging, and described legal pathways for protecting dedicated instream water (instream dedications and water-right transfers) but noted enforcement and monitoring resources remain challenges.
