Independent Experts Warn of Hazards of In-Stream Gravel Mining

By Scott Vouri / North Bay Progressive / April 4-17, 2002

Since the 1940s, millions of tons of gravel have been mined from the Russian River and its banks. This has and continues to happen in the drinking water supply for 600,000 people and the habitat for innumerable plant and animal species. Since the early 70’s scientists have documented the negative consequences of in-stream and open-pit gravel mining.

Recently however, natural resource specialists, hired by the mining industry to lobby government officials, have claimed that the currently practiced “bar-skimming” method of in-stream mining does not harm the watershed. These claims fly in the face of thousands of published studies and call into question the impartiality of the “experts” local electeds rely on to make findings of insignificant impacts. A major concern of planners and environmentalists is that in-stream gravel mining damages the spawning beds and habitat of migratory fish species such as the federally listed, threatened Coho, Chinook and steelhead salmon. Gravel mining consultants state that they have snorkeled with the fish during mining season dozens of times and have not seen the fish react adversely to the heavy mining equipment operating near-by. This argument side steps the issue, according to a study prepared for the National Marine Fisheries Service in late 2000 by Trinity Associates of Arcata. It lists the hazards that migratory fish encounter during spawning season, long after mining operators have left for the winter. Migratory fish lay their eggs in beds of larger sized gravel called cobbles. The cobbles prevent the eggs from being swept away by the current prior to gestation.

Skimming of gravel bars by mining operators, removes the top layer of cobbles and exposes finer gravels and sediment below, which cannot be used as spawning beds. In addition, the study found that channel bed scour was increased in riffles adjacent to skimmed bars, resulting in the loss of nest sites. Gravel bar skimming also changes the river channel configuration from narrow and deep to wide and shallow. The Trinity study showed that this reduction in flow depth and velocity caused higher summer temperatures and lower dissolved oxygen levels, both of which are harmful to coldwater fish such as salmon. Gravel bars are the primary location of the riparian vegetation which provides invertebrate food sources and water-cooling shade to migratory fish species during the summer and refuge from predators during high water months. Operators by necessity remove all vegetation from the bar sections to be mined. While modern practices do require operators to leave a small buffer of vegetation near the low water edge, seventy-five percent of the vegetation is removed, creating a wide, flat and warm summertime expanse of exposed streambed. The firm of Steiner Environmental Consulting found in a 1996 study performed in conjunction with the California Coastal Conservancy and the Sonoma County Water Agency that removal of riparian vegetation increases erosion and vertical bank formation, decreasing the interface between the river and the floodplain.

Given the documented potential damage from in-stream gravel mining, it is no wonder that the National Marine Fisheries Service (NMFS) is taking a go-slow approach to gravel mining projects. In April of 2001, James Bybee, NMFS Habitat Manager for Northern California wrote, “We are concerned about bar skimming actions and associated activities, and about potential changes in substrate, sediment transport, and habitat quality. These issues remain largely unresolved from our perspective.” The second major issue regarding in-stream gravel mining is its potential impact on drinking water supplies. In 1998 the Environmental Protection Agency and the State Water Resources Control Board declared the Russian River “impaired due to sedimentation/siltation”. The EPA’s list of potential sources of the sediment includes channel erosion, channelization, removal of riparian vegetation and stream bank destabilization. As early as 1994, Dr. Robert Curry, Professor of Environmental Geology at U.C. Santa Cruz, wrote that the sediment increase was due to oversteepened banks, trapped floodwaters and from the riverbed itself, unprotected by coarse gravel. In the same paper, Curry also postulated that the fine sediments cause of the decreased pumping capacity being experienced by the Sonoma County Water Agency at their Ranney collector water system, used to extract drinking water from the Russian River. Curry noted that in-stream gravel mining had caused fine sediments to plug the City of Ukiah’s Ranney collector system and they were forced by the State Department of Health to install a costly water treatment facility, bypassing the natural (and free) filtration process of the gravel aquifer.

The Northern Region Water Quality Control Board has weighed into the issue of substrate sediment “fines” exposed by gravel bar skimming. In the first decision of its kind, the Board is requiring monitoring of the sediment flow off of mined gravel bars during the high water months, as a condition of approval of a recently proposed project. “We are concerned about the sediment exposed on the gravel bars,” said Mark Nealy, Associate Engineering Geologist.

In an unfortunate case of déjà vu, the State Department of Health on August 24, 2000 notified the Sonoma County Water Agency that as part of its evaluation of the adequacy of the region’s water supplies, it had found that the Ranney collector system at Wohler Bridge was suffering from “impaired aquifer infiltration”.

There is one issue that every scientist who has looked at gravel mining impacts does seem to agree on. Removing more gravel in a single year than is what is brought downstream from the mountains during winter months is known to be a recipe for disaster. Fluvial geomorphologists state the river is a “dynamic system in equilibrium” – an equilibrium created by a constant amount of sediment and gravel always present in the system. If more gravel is removed from the system than is replenished, then the river restores the equilibrium by obtaining the gravel and sediment by eroding riverbanks, cutting a deeper incision into the river and tributaries and undermining bridges. According to the State Division of Mines and Geology’s 1990 Guide to Planners, bed lowering (incision) can in turn cause lowering of the groundwater table and loss of riparian habitat.

What many experts do not agree on is whether current mining practices in the Russian River are exceeding the annual replenishment rate. Each year the Sonoma County Permit and Resource Management Department releases a monitoring report, which estimates the amount of gravel within the River’s banks, based on cross-section measurements taken at various points along its length. In the most recent report, dated August 2001, the agency states that overall, there has been an increase in the average cross-sectional area of survey locations in the Middle, Healdsburg and Alexander Valley Reaches from 1994 to 2000. However, the report notes that only the Alexander Valley Reach (Cloverdale to Alexander Valley Bridge) has been subject to mining since 1994. For the Alexander Valley Reach, the report shows that there has actually been a decrease in average cross-sectional area for every location surveyed in the 18-mile stretch. The decrease in gravel area for the year 2000 averaged 42 square feet per survey site and 6 square feet per site for the entire period from 1994-2000.

In addition to measuring the area of exposed gravel for each year’s monitoring reports, agency contractors also measure the depth (above mean sea level) of the lowest point in the River at each survey location. This helps determine if a deeper incision is being cut into the riverbed. The report shows that while the average change in elevation for all survey points in the unmined Healdsburg and Middle Reaches was positive (0.2 feet) for the year 2000, the average change for the mined Alexander Reach was negative (-0.2 feet). Additionally, the report shows that for each of the last three years the number of survey points showing incision has increased each year.

Many experts argue that current in-stream mining practices, when compared to the egregiousness of past practices, are having negligible further impact on the Russian River. However, there is ample evidence that current practices are not allowing the River to heal from past abuses. Since the new bar skimming practices have been adopted, three salmon species have been listed as endangered, the region’s drinking water intake system has been declared impaired and not a single foot of the 20 feet in river bottom elevation lost since the 1940s has been recovered.