Validation of Rapid Assessment Methods to Determine Streamflow Duration Classes in the Pacific Northwest, USA

Abstract

United States Supreme Court rulings have created uncertainty regarding U.S. Clean Water Act (CWA) authority over certain waters, and established new data and analytical requirements for determining CWA jurisdiction. Thus, rapid assessment methods are needed that can differentiate between ephemeral, intermittent, and perennial streams. We report on the validation of several methods. The first (Interim Method) was developed through best professional judgment (BPJ); an alternative (Revised Method) resulted from statistical analysis. We tested the Interim Method on 178 study reaches in Oregon, and constructed the Revised Method based on statistical analysis of the Oregon data. Next, we evaluated the regional applicability of the methods on 86 study reaches across a variety of hydrologic landscapes in Washington and Idaho. During the second phase, we also compared the Revised Method with a similar approach (Combined Method) based on combined field data from Oregon, Washington, and Idaho. We further compared field-based methods with a GIS-based approach (GIS Method) that used the National Hydrography Dataset and a synthetic stream network. Evaluations of all methods compared results with actual streamflow duration classes. The Revised Method correctly determined known streamflow duration 83.9% of the time, versus 62.3% accuracy of the Interim Method and 43.6% accuracy for the GIS-based approach. The Combined Method did not significantly outperform the Revised Method. Analysis showed biological indicators most accurately discriminate streamflow duration classes. While BPJ established a testable hypothesis, this study illustrates the importance of quantitative field testing of rapid assessment methods. Results support a consistent method applicable across the Pacific Northwest.

Connectivity of Streams and Wetlands to Downstream Waters: An Integrated Systems Framework

“…Tracer experiments using 15 N, bromide, salt solutions, fluorescing particles, or other conservative compounds have also been conducted to assess the frequency, magnitude, and timing of flowpaths in aquatic systems (Mulholland et al 2004;Bencala et al 2011;O'Brien et al 2012). Furthermore, sensors that detect the presence of water in streams can be used to determine the duration of functional connections (McDonough et al 2015) and can assist in characterizing the hydrologic permanence of streams, which can inform estimates of the duration of connections (Leibowitz et al 2008;Fritz et al 2009;Nadeau et al 2015). Structural indices derived from topography, alone or in combination with other watershed characteristics (e.g., infiltration and storage capacity, presence of barriers), can be used to predict structural patterns in the spatial frequency, magnitude, and spatial extent of potential connections.…”

Quantifying spatial and temporal patterns of flow intermittency using spatially contiguous runoff data

“…Improved understanding of temporal and spatial patterns in flow intermittency is fundamentally important for effective river management (Snelder et al, 2013). However, this has been impeded by the scarcity of information about the distribution and hydrologic characteristics of intermittent streams (Acuña et al, 2017;Datry et al, 2011;Nadeau et al, 2015). This has resulted in increased research focus on quantifying the distribution of intermittent streams in particular geographic regions, such as France (Snelder et al, 2013), Australia (Kennard et al, 2010b), Spain and North America (de Vries et al, 2015).…”

Connectivity and Nitrate Uptake Potential of Intermittent Streams in the Northeast USA

“…Field surveys in nine regions of the US estimated that most regions have more than 200% intermittent stream channel length than depicted in NHDPlus maps (1: 24,000 or 1: 100,000 scales; Fritz et al, 2013). Nadeau et al (2015) also found poor agreement between field verified intermittent streams and USGS 1:24,000 maps in the Pacific Northwest. We found that the percent of wetlands connected to stream outlets by intermittent streams was 135% higher than our estimate of such wetlands from NHDPlus HR geospatial data.…”

“…However, the value of these non-perennial waterways for protection has been undermined by the historical gap in identifying the extent and connectivity of these intermittent and ephemeral streams on maps of common scale (i.e., 1:24,000; Leibowitz et al, 2008;Benstead and Leigh, 2012;Datry et al, 2014;Ryan, 2017;Wohl, 2017). With the advancement of improved mapping, modeling, and field work in recent years, the extent and functional importance of intermittent streams (Benstead and Leigh, 2012;Fritz et al, 2013;Leigh et al, 2015;Nadeau et al, 2015;Williamson et al, 2015) and their connections to wetlands (Tiner, 2003;Marton et al, 2015;Lane and D'Amico, 2016;Rains et al, 2016) can be refined.…”