Dam removal provides a valuable opportunity to measure the fluvial response to changes in both sediment supply and the processes that shape channel morphology. We present the first study of river response to the removal of a large (32‐m‐high) dam in a Mediterranean hydroclimatic setting, on the Carmel River, coastal California, USA. This before‐after/control‐impact study measured changes in channel topography, grain size, and salmonid spawning habitat throughout dam removal and subsequent major floods. During dam removal, the river course was re‐routed in order to leave most of the impounded sediment sequestered in the former reservoir and thus prevent major channel and floodplain aggradation downstream. However, a substantial sediment pulse occurred in response to base‐level fall, knickpoint migration, and channel avulsion through sediment in the former reservoir above the newly re‐routed channel. The sediment pulse advanced ~3.5 km in the first wet season after dam removal, resulting in decreased riverbed grain size downstream of the dam site. In the second wet season after dam removal, high flows (including a 30‐year flood and two 10‐year floods) transported sediment > 30 km downstream, filling pools and reducing cross‐channel relief. Deposition of gravel in the second wet season after dam removal enhanced salmonid spawning habitat downstream of the dam site. We infer that in dam removals where most reservoir sediment remains impounded and where high flows follow soon after dam removal, flow sequencing becomes a more important driver of geomorphic and fish‐habitat change than the dam removal alone. © 2018 John Wiley & Sons, Ltd.

a b s t r a c tStudy region: The Salmon River is the second largest tributary of the Klamath River in northern California, USA. It is a region of steep mountains and diverse conifer forests. Historical land uses including logging, flow diversions, and hydraulic gold mining, have resulted in altered sediment transport regimes, diminished riparian cover and reduced large woody debris. These in turn have altered the thermal regime of the river. Summer stream temperatures commonly exceed salmonid (specifically Oncorhynchus spp.) temperature thresholds. Study focus: Thermal dynamics of a one-kilometer reach of the Salmon River was quantified using distributed temperature sensing fiber-optics (DTS) and Heat Source modeling. Stream thermal responses to scenarios of air temperature increase and flow reduction were compared with riparian reforestation simulations to estimate benefits of reforestation. New hydrological insights: Elevated air temperatures (2 • C, 4 • C, 6 • C) increased mean stream temperature by 0.23 • C/km, 0.45 o C/km and .68 • C/km respectively. Reforestation lowered temperatures 0.11-0.12 • C/km for partial and 0.26-0.27 • C/km for full reforestation. Reduced streamflow raised peak stream temperatures in all simulations. Warming could be mitigated by reforestation, however under severe flow reduction and warming (71.0 % reduction, 6 • C air temperature), only half of predicted warming would be reduced by the full reforestation scenario. Land managers should consider reforestation as a tool for mitigating both current and future warming conditions.

Over the last three decades, passive integrated transponder (PIT) tags have been widely used to study fish populations. Interpretation of PIT tag detections, however, can be confounded by the presence of ghost tags, tags liberated when a fish dies. We used a combination of mobile antenna surveys, stationary antenna detections, and multistate mark–recapture modeling to assess the abundance and fate of ghost tags in a coastal California watershed. Accumulation of ghost tags from released hatchery-origin coho salmon (Oncorhynchus kisutch) smolts was substantial during California’s recent drought, with 2224 ghost tags identified during mobile reader surveys. Between surveys, PIT tags moved downstream a median distance of 346 m and a maximum distance of 1982 m. Stationary antenna array detections indicated that these movements occurred during high-flow events, concurrent with live fish movement. The multistate model estimated that, during winter, approximately 40% of tags were buried in the substrate beyond the read range of mobile readers. Failure to account for transport and burial dynamics of ghost tags can lead to biased estimates of fish abundance, survival, and movement.