Predictors of urban variable source area: a cross‐sectional analysis of urbanized catchments in the United States

Abstract

Many studies have empirically confirmed the relationship between urbanization and changes to the hydrologic cycle and degraded aquatic habitats. While much of the literature focuses on extent and configuration of impervious area as a causal determinant of degradation, in this article, I do not attribute causes of decreased watershed storage on impervious area a priori. Rather, adapting the concept of variable source area (VSA) and its relationship to incremental storage to the particular conditions of urbanized catchments, I develop a statistically robust linear regression‐based methodology to detect evidence of VSA‐dominant response. Using the physical and meteorological characteristics of the catchments as explanatory variables, I then use logistic regression to statistically analyze significant predictors of the VSA classification. I find that the strongest predictor of VSA‐type response is the percent of undeveloped area in the catchment. Characteristics of developed areas, including total impervious area, percent‐developed open space and the type of drainage infrastructure, do not add to the explanatory power of undeveloped land in predicting VSA‐type response. Within only developed areas, I find that total impervious area and percent‐developed open space both decrease the odds of a catchment exhibiting evidence of VSA‐type response and the effect of developed open space is more similar to that of total impervious area than undeveloped land in predicting VSA response. Different types of stormwater management infrastructure, including combined sewer systems and infiltration, retention and detention infrastructure are not found to have strong statistically significant effects on probability of VSA‐type response. VSA‐type response is also found to be stronger during the growing season than the dormant season. These findings are consistent across a national cross‐section of urbanized watersheds, a higher resolution dataset of Baltimore Metropolitan Area watersheds and a subsample of watersheds confirmed not to be served by (combined sewer systems). Copyright © 2016 John Wiley & Sons, Ltd.

Effects of spatial configuration of imperviousness and green infrastructure networks on hydrologic response in a residential sewershed

“…Impervious surface area has emerged has emerged as the dominant explanation for reduction of subsurface storage in urbanized watersheds [ Schueler , ; Arnold and Gibbons , ; Moglen and Kim , ]. However, impervious surface area may not be the dominant explanation for changes in the urban hydrological cycle [ Bhaskar et al ., ; Smith et al ., ; Lim , ]. Subsurface dynamics, inter‐event capacity recovery through evapotranspiration from vegetation and potential interactions between overland flow and the differential contraction of saturated areas, and lower than expected hydraulic conductivity of urban soils are offered as possible explanations for changes in the hydrological cycle associated with urbanization.…”

“…The concept of Urban Variable Source Area (UVSA) is an adaptation of Dunne's Variable Source Area (VSA), which states that heterogeneity of infiltration rates within a watershed has not only to do with the heterogeneity of soils; it is also dynamically related to the behavior of water over the topography of the landscape and in heterogeneous interactions with subsurface (shallow groundwater) capacity of soil [ Dunne et al ., ]. UVSA extends idea to apply to urbanized areas, were high levels of spatial‐temporal heterogeneity in topography, drainage infrastructure, buildings, human activities (such as lawn watering), and surface and subsurface conditions would be expected to dynamically affect the variable source area phenomenon [ Miles and Band , ; Lim , ].…”

An analytical approach to ascertain saturation‐excess versus infiltration‐excess overland flow in urban and reference landscapes

“…The ability to integrate SEOF and IEOF processes together becomes particularly important in urban settings, where heterogeneity in soil conditions and land cover increases the complexity of infiltration and saturation processes (Lim, ; Miles & Band, ). Although infiltration rates of urban soils are commonly analysed as point measurements (Schifman & Shuster, ; Schifman, Tryby, Berner, & Shuster, ; Shuster, Dadio, Drohan, Losco, & Shaffer, ), a lack of understanding exists on which processes drive urban soils to generate run‐off.…”

Assessing Variability and Uncertainty in Green Infrastructure Planning Using a High-Resolution Surface-Subsurface Hydrological Model and Site-Monitored Flow Data

“…However, the above examples highlight why a more flexible conceptual model that incorporates surfacesubsurface and infrastructure interactions may be necessary. The Urban Variable Source Area (UVSA) and watershed capacitance conceptual model can help organize the conditions when specific properties of the urbanized catchment, including soil permeability, slope, depth to groundwater, land use and land cover, and availability and placement of infiltration opportunities, will influence how runoff is generated under different meteorological and morphological conditions, as is shown in Figure 1 (Miles and Band, 2015;Lim, 2016). The above examples and the UVSA conceptual model suggests that GI may exhibit a trade-off in cumulative effectiveness during very wet conditions, multiday events, when watershed capacitance is limited, or when infiltration opportunities are clustered together in high flow accumulation areas.…”

“…SALDOs stipulate that the owners must implement stormwater control measures on their properties to meet some design standard (for example, store and treat runoff resulting from the properties impervious surfaces for the 1-year, 24-h rain event). However, in order to speed the adoption of green infrastructure practices on private property above the redevelopment rate, some FIGURE 1 | Conceptual model of factors influencing areas contributing runoff in an urbanized catchment area (adapted from Lim, 2016). Conventional and green infrastructure placement and density mediates balance between dominance of Hortonian flow, saturation overland flow, and subsurface stormflow processes at the catchment scale.…”