Definition: The area near
upland human altered drainage pathways (i.e., gutters, swales) that can assume
some of the aquatic ecosystem functions of a natural riparian zone.
Explanation: Normally, small headwater stream functions are
defined by riparian (nearby) forested areas, which cool waters in the summer
and supply organic matter (e.g., leaves, wood) to these streams as well as
downstream aquatic ecosystems. In
urbanized landscapes however, these small headwater streams are augmented by
the engineered drainage system, which greatly expand the area the organic
matter sources, from “just riparian” to most of the urban landscape. Streets, driveways, parking lots and gutters
form dense networks of drainage pathways which act as greatly expanded small
streams (i.e., zero order, ephemeral streams) which carry organic matter and
pollutants directly to small headwater streams with every rainstorm.
Example: In a dense suburban landscape such as Dead
Run, the storm drainage gutter networks facilitate the movement of organic
matter (trees, grass, trash, animal waste) to stormdrains and downstream
headwater streams. The areas around
these gutters (and other drainage features) therefore act as “upland riparian
zones” for the watershed wide areas of the landscape, with functions that are
similar to natural “riparian” zones (near streams.) These include temperature modification (where
there are nearby shade trees) and providing organic matter sources (leaves,
grass, wood) for downstream food webs.
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Figure
1: Curbs and gutters of urbanized areas
greatly expand the drainage density and therefore the fluxes of organic matter,
stormwater and pollutants to small headwater streams
Left: Expanded upland riparian zones (hatching) compared
to the natural riparian areas (blue lines) from the pre-development state;
Right: Sidewalks, gutters and driveways, along with nearby vegetation which
form an upland riparian zone (URZ) in the suburban Spring Branch catchment.
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Why Important: The drainage
density (i.e., drainage miles per watershed area) of natural streams is dwarfed
by urban systems, increasing landscape-stream connectivity greatly. This creates high loads to streams of both
natural (e.g., leaves) and unnatural (e.g., oil, metals, bacteria, etc.)
constituents, magnifying the urban stream syndrome effect and greatly impacting
stream ecological structure and function.
Contributed by BES Co-PI Kenneth T. Belt
