ASSESSING AND MANAGING THE EFFECTS OF IN-STREAM MINING IN CALIFORNIA

In-stream mining operations are an essential part of California's future as they provide an important source of aggregate to the construction industry and can help maintain flood control. In California, in-stream mining operations are regulated in part by the Surface Mining and Reclamation Act (SMARA) which requires mining operations to control channel degradation and to evaluate channel elevations and bank erosion annually. The extraction of sand and gravel from California’s river systems can affect flow, sediment sources, and sediment transport, and may result in changes to the channel morphology. Primary in-stream mining methods used in California include stream bed skimming, in-stream pit mining, and floodplain pit mining. Effects from these mining methods can include aggradation, channel incision, headward erosion (headcutting), bank erosion, channelization, loss of low flow channel confinement, disrupting bed armor, pit capture, loss of soil development on floodplains, lower groundwater levels, loss of riparian vegetation, loss of wildlife habitat, and damage to infrastructure. These effects can be minimized or eliminated through proper planning (including the development of regulations or oversight committees), assessments, and monitoring. One strategy, called adaptive management, consists of limiting extraction rates to an amount less than the estimated sediment supply from upstream sources. Assessments typically include reviewing survey data to estimate the amount of recruitment and then limiting annual extraction rates. Long-term monitoring may be necessary through the implementation of a watershed-scale adaptive management plan because some effects may not be immediately obvious since they are dependent on high flow conditions.