You are here:
Verification of Hydrologic Landscape Derived Basin-Scale Classifications in the Pacific Northwest
Citation:
Sawicz, K., S. Leibowitz, R. Comeleo, AND P. Wigington, Jr. Verification of Hydrologic Landscape Derived Basin-Scale Classifications in the Pacific Northwest. 2015 Fifth Interagency Conference on Research in the Watershed, Charleston, SC, March 02 - 05, 2015.
Impact/Purpose:
EPA’s Western Ecology Division has published and continues to expand a framework for defining areas of the landscape that are hypothesized to have similar hydrologic responses. These hydrologic landscapes (HL) were developed to help characterize duration of flow in non‐navigable streams, to examine how non‐navigable streams influence and contribute to the integrity of navigable waters. Previous work defined HLs across Oregon and described climatic and physical properties for over 5000 assessment units. This approach was then extended the HL framework to the three Pacific Northwest (PNW) states of Washington, Oregon and Idaho. The HLs were developed using the National Hydrography Dataset’s WBD HU12 scale that are comprised of classification components describing climate, climate seasonality, aquifer permeability, terrain, and soil permeability. This approach can only be useful for water and ecological management if the extended HLs accurately represent hydrologic behavior at these assessment units. To test the assumptions presented by the HL framework, we developed methodologies to aggregate the information represented within the HLs to the catchment scale across our dataset of 199 catchments to be analyzed against the input/output of water in the catchment. HL aggregation must preserve information on the location of the HL within the catchment outlet (upstream vs. downstream) and properties of that HL (i.e. water source vs. sink). We investigated catchment response by comparing hydrologic behavior between different HL classes. We derived hydrologic signatures from long term time series of flow into and out of the catchment to capture the hydrologic behavior for catchments in the Pacific Northwest, and include, Runoff Ratio, Baseflow Index, Snow-to-Total Precipitation Ratio, and Recession Coefficients. We then performed statistical analysis of signature values and trends with respect to aggregated HL classification. This presentation will include the end product of the Pacific Northwest HLs, methods of the aggregation of physical and climatic attributes to the catchment scale, and relate that catchment scale information to long term streamflow characteristics in a multidisciplinary federal interagency scientific setting.
Description:
The interaction between the physical properties of a catchment (form) and climatic forcing of precipitation and energy control how water is partitioned, stored, and conveyed through a catchment (function). Hydrologic Landscapes (HLs) were previously developed across Oregon and describe climatic and physical properties for over 5000 assessment units. This approach was then extended to the three Pacific Northwest states of Washington, Oregon and Idaho (PNW HL). The HLs were developed using the National Hydrography Dataset’s WBD HU12 scale and are comprised of classification components describing climate, climate seasonality, aquifer permeability, terrain, and soil permeability. Catchment function was investigated through derivation of hydrologic signatures for catchments in the Pacific Northwest, which are attributes of long-term time series of water into and out of the catchment. To compare the PNW HL classification to hydrologic behavior, we developed methodologies to aggregate and interpret information provided by HLs to the catchment scale to compare signature values and trends with respect to aggregated HL classification. HL aggregation must preserve information on the location of the HL within the catchment outlet (upstream vs. downstream) and properties of that HL (i.e. water source vs. sink). Signatures include Runoff Ratio, Baseflow Index, Snow Ratio, and Recession Coefficients. We hypothesize that we will find: 1) a rational way to combine HL information to characterize catchment-scale areas 2) strong relationships between aggregated HLs and hydrologic signatures; 3) signatures related to water balance are explained by climatic conditions; and 4) signatures describing flow paths are predicted by terrain, soil, and aquifer permeability. This study examined 199 catchments to achieve objectives and test hypotheses stated.