Coastal Streams in Central California Reflect the Region’s Drought
It’s no secret that water is a crucial resource. Not only do we require it for drinking, but also for many other basic necessities, such as sanitation and irrigation. In the western United States water is not as abundant as in many other parts of the country; in some periods, less rain falls and water is even scarcer. We are now in one of those periods: 2013 was the driest calendar year on record for the state of California (see “The California Drought”), prompting Governor Jerry Brown to declare a drought state of emergency on January 17, 2014.
The U.S. Geological Survey (USGS) Water Science Centers monitor the nation’s many rivers and keep records for each stream gage. These records, some of which go back for decades, typically include not only the stream height and the amount of water flowing past the gage, but also such factors as temperature, pH, conductivity, and sedimentation. These records can be used as a sort of almanac to show the median value for flow that can be expected at a given site during a certain time of year. They also enable us to compare one year to another to get a general sense for how current conditions compare to those measured in the past.
USGS personnel in the California Water Science Center’s Santa Cruz Field Office monitor streams along the central California coast from Pilarcitos Creek at Half Moon Bay to the Salinas River in Paso Robles. For every gage on every stream, they determine the relation between discharge (amount of water flowing past the gage, in cubic feet per second, or cfs) and stage (height of water relative to a reference elevation, in feet). To do so, they manually measure discharge and stage over a wide range of river stages. (Learn more about this process at “How Streamflow is Measured Part 3: The stage-discharge relation.”) Establishing this relation permits automated data collection: a sensor in the river takes a stage reading every 15 minutes. Every hour these data are transmitted by satellite to the USGS National Water Information System (NWIS), where the corresponding discharge is computed. Stage, discharge, and any other data that are being collected—such as water temperature—are posted on the NWIS Web Interface. Thus users such as the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service, local agencies and communities, and interested members of the general public have access to stream information in near-real time.
Information about stage is particularly important during or after periods of heavy precipitation when flooding is a concern. During normal conditions, and especially during times of drought, local managers need information about discharge to help them decide how much water can be pumped from a stream, how much must be left for fish, and so on. Because of the importance of stream-gage data, they are cross-checked and reviewed in many ways: every month, personnel from the USGS Santa Cruz Field Office compare the stream heights measured by sensors with readings on a staff plate, a large ruler installed vertically in the water, to make sure the measurements match. Likewise, they check calculated discharge values against discharge measurements they make manually. They also check to see that data pulled directly from storage devices in the gage house match those that were transmitted to NWIS. After several months, the amassed data are closely examined for errors; online data that have not yet received this review are labeled “provisional.”
The effects of California’s drought are vividly illustrated in the discharge data from streams in the Santa Cruz area. One of these streams, the San Lorenzo River, flows through Santa Cruz and into Monterey Bay. It is a primary water source for the city. On the basis of the 77 years of records available, we would expect it to flow at around 25 cfs in a typical July, but discharge in July 2014 was only around 10 cfs. Records of discharge in Pescadero Creek, which flows into the Pacific Ocean approximately 50 kilometers (30 miles) northwest of Santa Cruz, go back 63 years and indicate that the stream would normally be flowing around 4 cfs in the month of July, but it was barely more than 0.3 cfs in July 2014. Other nearby streams were also flowing at rates much lower than usual in July 2014.
The primary concern in drought is that we have enough water for drinking and for such everyday activities as washing and watering, but having abnormally low amounts of water in a river causes other concerns as well. In addition to human consumption, water is necessary to maintain life both in rivers (aquatic) and in areas adjacent to rivers (riparian). Steelhead trout, for example, spawn in the San Lorenzo River, Pescadero Creek, and other central California coastal streams. These fish are born in rivers, travel out to the ocean, and later return to the river of their birth to spawn the next generation. Such anadromous species require access from the ocean to the rivers in order to swim upstream. When the river runs dry, the fish cannot get back to their spawning grounds. This is just one example; there are many other species that are threatened by droughts.
One of the central California streams that hosts steelhead trout is the Carmel River, which flows into the Pacific Ocean about 50 kilometers (30 miles) south of Santa Cruz. USGS water scientists stationed in Santa Cruz monitor a stream gage on the downstream stretch of the Carmel River (USGS 11143250 CARMEL R NR CARMEL CA) that commonly goes dry during California’s long dry summers. In fact, this gage has been dry since May 2013, with the exception of 12 days in March and April 2014. This dry spell may remind some locals of the drought of 1976–77, when USGS records show that this section of the Carmel River was dry from May 13, 1976, through December 17, 1977. Fortunately for the trout population in the Carmel River, biologists from government agencies travel the river, capture the fish, and relocate them upstream where there is more water.
According to news released by NOAA on October 16, 2014, “California’s record-setting drought will likely persist or intensify in large parts of the state.” It remains to be seen whether the state’s winter wet season will provide some relief, particularly the mountain snowfall described by NOAA as “crucial for drought recovery.” Meanwhile, groups and individuals should continue to conserve water.
in this issue:
Coastal Streams in Central California Reﬂect the Region’s Drought