Headwater stream morphology and sensitivity to development in the Piceance Basin of western Colorado

Abstract

Headwater streams are important components of watershed networks, but are less studied than larger channels and lack regulatory protection. Despite the small size of these streams, they have a disproportionate impact on the health of the watershed. Development of energy resources in the Piceance Basin of western Colorado is potentially causing significant changes in water and sediment yields to these headwater streams through the construction of roads and infrastructure. Additionally, the importance of headwater streams implies that understanding channel initiation is valuable for delineating and managing headwater stream systems. This research investigates two aspects of headwater streams: the potential impacts of energy development on channel morphology and the characterization of channel heads in western Colorado. The study focusing on channel morphology and energy development tests three hypotheses: 1) the morphology of headwater streams proximal to energy development is significantly different than otherwise analogous streams, 2) stream sensitivity to development will vary with respect to underlying lithology, and 3) stream sensitivity to development will vary with respect to stream gradient. The study exploring channel heads in western Colorado has two main objectives: 1) examine the effects of surface and subsurface flow, underlying lithology, and local gradient on channel head characteristics, and 2) examine differences between channel heads in diverse study regions by comparing this dataset to published datasets. A total of 94 stream reaches were chosen for assessing channel response to energy development. Of these, 49 reference reaches have little or no upstream disturbances and 45 impacted streams are located immediately downstream of a road or well pad. Three cross-sections per reach were surveyed to determine gradient and width to depth ratio; this ratio was used to represent channel morphology. A variety of statistical methods, including ANOVA and pairwise comparisons, were used to investigate the influence of energy development on channel morphology. This study found limited connection between energy development and headwater channel morphology. Although the morphology of impacted stream reaches is not significantly different from reference reaches, there is a relationship between channel morphology and distance to impact. Additionally, 38 channel heads were selected for analysis, including both channel heads with surface and subsurface flow, and channel heads with underlying shale and sandstone lithology. ArcGIS was used to calculate channel head parameters, including contributing drainage area and local gradient. Boxplots and the non-parametric Wilcoxon Rank Sum test were used to compare the variables drainage area, local gradient, and basin length between sandstone and shale lithologies and between subsurface and surface flows. Regression equations and pairwise comparisons were used to compare datasets from differing geographic regions. Channel heads with subsurface runoff have significantly different characteristics than channel heads with surface runoff. Differences are also present between channel heads with different underlying lithologies. No notable differences were found between channel heads located in western Colorado and other study regions.