Similarity of stream width distributions across headwater systems

Abstract

The morphology and abundance of streams control the rates of hydraulic and biogeochemical exchange between streams, groundwater, and the atmosphere. In large river systems, the relationship between river width and abundance is fractal, such that narrow rivers are proportionally more common than wider rivers. However, in headwater systems, where many biogeochemical reactions are most rapid, the relationship between stream width and abundance is unknown. To constrain this uncertainty, we surveyed stream hydromorphology (wetted width and length) in several headwater stream networks across North America and New Zealand. Here, we find a strikingly consistent lognormal statistical distribution of stream width, including a characteristic most abundant stream width of 32 ± 7 cm independent of discharge or physiographic conditions. We propose a hydromorphic model that can be used to more accurately estimate the hydromorphology of streams, with significant impact on the understanding of the hydraulic, ecological, and biogeochemical functions of stream networks.

The Abundance, Size, and Spacing of Lakes and Reservoirs Connected to River Networks

“…Connected lakes/reservoirs were then identified as the remaining lakes/reservoirs that spatially intersect the perennial river network and have surface water connectivity (an inlet and/or outlet) because a connected lake/reservoir of any size may influence geomorphic, ecological, and hydrologic processes of the connected river and vice versa. We recognize NHD data may not be accurate for the smallest rivers and lakes/reservoirs (Allen et al, ; Benstead & Leigh, ), but our results should not be impacted given our focus on perennial rivers/lakes/reservoirs at the spatial scale of Hydrologic Unit Code 6 (HUC6) watershed boundaries (~25,000 km 2 ) and the contiguous United States. A higher resolution river network data set would add mostly temporary streams, perhaps increasing the abundance of connected lakes/reservoirs in small streams, but without impacting downstream results.…”

Observing Rivers With Varying Spatial Scales

“…We note that if the parameters are normally distributed about their mean, ϵ i will be normally distributed with zero mean. If, as seems more likely given observations by Allen et al (2018), Frasson et al (2019), Moody and Troutman (2002), they are lognormal, then ζ i will be normally distributed, with mean given by where we used equation .…”

“…To illustrate the concepts, we introduce in section 5.2 a simple model for a riffle and pool sequence that can be solved exactly and at arbitrary spatial resolution for gradually varied flow. A study of more complicated river conditions is then presented in section 5.3, where we characterize the changes in the friction coefficient that are observed by reach averaging the calibrated hydraulic models and compare the exact results with simple estimates that are obtained assuming a lognormal distribution of hydraulic parameters, as been suggested by Moody and Troutman (2002) and more recently by Allen et al (2018). We show that this simplifying assumption provides reasonable estimates for changes in the friction coefficient which do not require detailed knowledge at scales smaller than a river reach.…”

How Hydrologic Connectivity Regulates Water Quality in River Corridors

“…At present, only hyporheic zones and turbulent mixing have been modeled, and there is need to consider more types of reaction zones such as floodplains. Also, the river network that we considered does not include the smallest streams, which are difficult to map comprehensively (Allen et al 2018). Eventually there will be improvements in regional mapping that will allow their inclusion.…”