U.S. Geological Survey Streamgage Research Articles

Forest cover lessens the impact of drought on streamflow in Puerto Rico

AbstractTropical regions are experiencing high rates of forest cover loss coupled with changes in the volume and timing of rainfall. These shifts can compromise streamflow and water provision, highlighting the need to identify how forest cover influences streamflow generation under variable rainfall conditions. Although rainfall is the key driver of streamflow regimes, the role of forests is less clear, particularly in tropical regions where forest loss is an ongoing risk. Forest cover loss alters evapotranspiration, rainfall infiltration and storage, and may increase stream ecosystem vulnerability to rainfall extremes. Puerto Rico, an island with spatially heterogenous forest cover and a marked geographic rainfall gradient, is projected to experience more frequent droughts and flash flooding. Using 15‐min streamflow data collected between 2005 and 2016 from 20 US Geological Survey stream gages and 3‐hourly Multi‐Source Weighted‐Ensemble Precipitation rainfall estimates, we utilized flow‐duration curves and linear mixed regression models to examine the role of forest cover in regulating the timing and volume of streamflow. The mixed model approach helps to account for differences in watershed characteristics. We determined the effects of rainfall and forest cover on low and peak flows in Puerto Rican streams, then evaluated changes in these relationships under dry and wet antecedent rainfall conditions. Watersheds with high forest cover had consistently greater low and peak streamflow than deforested ones under all rainfall conditions, although the effect was more marked during wet antecedent conditions, suggesting that peak flow is largely the result of saturation excess overland flow. During dry antecedent rainfall conditions, highly forested watersheds had higher streamflow than deforested ones, suggesting greater hillslope storage and release may also be at play. Our results demonstrate that forest cover generated a net increase in hillslope infiltration and storage and may lessen drought impacts on streamflow in Puerto Rico. Resilience to prolonged drought may be limited by finite water storage potential in this steep, mountainous setting, highlighting maintenance of forest cover as an important water management strategy to increase infiltration.

Updating estimates of low-streamflow statistics to account for possible trends

ABSTRACT Accurate estimators of streamflow statistics are critical to the design, planning, and management of water resources. Given increasing evidence of trends in low-streamflow, new approaches to estimating low-streamflow statistics are needed. Here we investigate simple approaches to select a recent subset of the low-flow record to update the commonly used statistic of 7Q10, the annual minimum 7-day streamflow exceeded in 9 out of 10 years on average. Informed by low-streamflow records at 174 US Geological Survey streamgages, Monte Carlo simulation experiments evaluate competing approaches. We find that a strategy which estimates 7Q10 using the most recent 30 years of record when a trend is detected, reduces error and bias in 7Q10 estimators compared to use of the full record. This simple rule-based approach has potential as the basis for a framework for updating frequency-based statistics in the context of possible trends.

Satellite remote sensing estimation of river discharge: Application to the Yukon River Alaska

A methodology based on general hydraulic relations for rivers has been developed to estimate the discharge (flow rate) of rivers using satellite remote sensing observations. The estimates of discharge, flow depth, and flow velocity are derived from remotely observed water surface area, water surface slope, and water surface height, and demonstrated for two reaches of the Yukon River in Alaska, at Eagle (reach length 34.7 km) and near Stevens Village (reach length 38.3 km). The method is based on fundamental equations of hydraulic flow resistance in rivers, including the Manning equation and the Prandtl-von Karman universal velocity distribution equation. The method employs some new hydraulic relations to help define flow resistance and height of the zero flow boundary in the channel. Estimates are made both with and without calibration. The water surface area of the river reach is measured by using a provisional version of the U.S. Geological Survey (USGS) Landsat based product named Dynamic Surface Water Extent (DSWE). The water surface height and slope measurements require a self-consistent datum, and are derived from observations from the Jason-2 satellite altimeter mission. At both reach locations, the Jason-2 radar altimeter non-winter heights consistently tracked the stage recorded at USGS streamgages with a standard deviation of differences (error) during the non-winter periods of less than 7%. Part of the error may be due to differences in the gage and altimeter crossing locations with respect to the range of stage change and the response to changes in discharge at the upstream and downstream locations. For the non-winter periods, the radar derived slope estimates (mean = 0.0003) were constant over the mission lifetime, and in agreement with previously measured USGS water surface slopes and slopes determined from USGS topographic maps. The accuracy of the mean of the uncalibrated daily estimates of discharge varied between reaches, ranging from 13% near Stevens Village (N = 90) to −21% at Eagle (N = 246) based on the absolute error, and 5% to −6% based on the error of the log of the estimates. Calibrating to the mean of USGS daily discharge estimates from the streamflow rating for the same period of record at each streamgage resulted in mean absolute errors ranging from 1% to 2%, and log errors ranging from 1% or less. The error pattern of the estimates shows that without calibration, even though the mean is well simulated, the high and low end values over the range of estimates may have significant bias.

Body-shape variation ofAcroneuria lycorias(Plecoptera∶Perlidae) nymphs across magnitude and frequency stream flows

AbstractMorphological variation across environmental gradients can indicate an organismal phenotypic response to the surrounding environment. The interaction of body shape and water movement creates physical forces that can affect the ecology and evolution of benthic organisms in stream systems. Magnitude and frequency components of flow regimes have been linked to morphological variation in body shape of fish and macrophytes, but very few attempts have been made to evaluate similar relationships in stream insects. The aim of our study was to evaluate body-shape variation in large nymphs of an insect species and to test for a correlation with natural streamflow fluctuations in a regional geographic space. We sampled Acroneuria lycorias (Plecoptera∶Perlidae) populations at 9 stream sites (8 systems) with an associated US Geological Survey stream gage. We calculated ecological flow statistics from daily discharge data, and we used 2-dimensional geometric morphometrics to describe variation in A. lycorias bo...

MACROINVERTEBRATE COMMUNITY CONDITION ASSOCIATED WITH THE SEVERITY OF STREAMFLOW ALTERATION

ABSTRACTNatural streamflows play a critical role in stream ecosystems, yet quantitative relations between streamflow alteration and stream health have been elusive. One reason for this difficulty is that neither streamflow alteration nor ecological responses are measured relative to their natural expectations. We assessed macroinvertebrate community condition in 25 mountain streams representing a large gradient of streamflow alteration, which we quantified as the departure of observed flows from natural expectations. Observed flows were obtained from US Geological Survey streamgaging stations and discharge records from dams and diversion structures. During low‐flow conditions in September, samples of macroinvertebrate communities were collected at each site, in addition to measures of physical habitat, water chemistry and organic matter. In general, streamflows were artificially high during summer and artificially low throughout the rest of the year. Biological condition, as measured by richness of sensitive taxa (Ephemeroptera, Plecoptera and Trichoptera) and taxonomic completeness (O/E), was strongly and negatively related to the severity of depleted flows in winter. Analyses of macroinvertebrate traits suggest that taxa losses may have been caused by thermal modification associated with streamflow alteration. Our study yielded quantitative relations between the severity of streamflow alteration and the degree of biological impairment and suggests that water management that reduces streamflows during winter months is likely to have negative effects on downstream benthic communities in Utah mountain streams. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Quantifying the effect of land use land cover change on increasing discharge in the Upper Mississippi River

Summary There is convincing evidence that land use/land cover (LULC) change has contributed to increasing discharge in the Upper Mississippi River Basin (UMRB) but key details remain unresolved. In this study, we extend our previous work ( Zhang and Schilling, 2006 ) to quantify how much of the increasing discharge was due to LULC change. We examined daily streamflow for the 1890–2003 period from the US Geological Survey stream gage at Keokuk, Iowa and compiled county agricultural statistics for soybean production in the watershed above the gage to quantify how much of the change in the relation of discharge to precipitation was due to increased soybean cultivation. By allowing the slope of the discharge–precipitation relationship to be a function of the area of the UMRB planted in soybean, we determined that increasing soybean acreage increased the slope of qt–Pt by 32%. With row crop expansion anticipated from ethanol production, increasing agricultural production is expected to result in increased water yield and nutrient export. Results provide important benchmarks for assessing the significance of LULC change on the regional water and climate patterns in the UMRB.

Fewer USGS Streamgaging Stations could pose problems for flood forecasting, Report cautions

Although the risk of flooding along rivers has not decreased in the United States over the past several decades, the number of stations in the U.S. Geological Survey's (USGS) streamgaging network has dropped significantly during that same time period, according to a new report by the agency to Congress, “A New Evaluation of the USGS Streamgaging Network.”The decline in streamgaging stations also is affecting the ability to forecast long‐term changes and determine water quality, the report states.