Upland Riparian Zone (URZ)

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.

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.

 

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