Parametric examination of source area snowmelt clarification

Christopher M. Dean, Kim M. Howerter and John J. Sansalone


Irrespective of precipitation conditions, modern urban design, anthropogenic activities, in particular, transportation generates a wide spectrum of anthropogenic soluble and particulate constituents. Through precipitation events (snow or rain) these constituents partition, are distributed across the available granulometry. In source area watersheds dominated by pavement and traffic, a wide gradation of granulometry is transported and temporarily deposited in conveyance systems on the way to control (hydrologic, physical and chemical). Detention of runoff is a commonly applied stormwater management control strategy with potential to provide hydrologic and water chemistry (particulate phase) benefits. Detention can also be an effective and economical hydrologic and particulate control for snow dump sites. Many studies have reported on the behavior of detention basins for an aggregate measure of solids, measured as (TSS), transported in runoff. In contrast, this study reviews the role of process design parameters (steady flow, Q and basin area, A) on primary clarification of discrete particle sizes across the entire snow particulate gradation. The study employs the use of Hazen’s model, a semi-empirical model for particle settling, in contrast to conventional overflow rate theory for clarification of snowmelt runoff. This study also demonstrates that knowledge of the granulometric distribution of constituent (in this case particulate-bound metal mass) and flow characteristics allows the designer to estimate effectiveness of a given design for a single particle size or across the entire gradation for a combination of Q, A or non-ideal basin conditions (through Hazen’s N for hydrodynamic characterization). Results are applied to an existing snowmelt basin loaded by snowmelt sheet flow off the South Lake Tahoe snow dumpsite. Results demonstrated that the existing basin design provides the potential for high removal efficiencies for particulate mass and particulate-bound metal mass. These results are clearly a function of the coarse granulometry trapped in the snow that had been dumped and graded into organized rows for drainage directly into the basin; as well as the low and extended sheet flow drainage rates into the basin. Hydrologic and water chemistry are coupled phenomena, and for this application, detention appears to be an economical passive strategy for hydrology and chemical (particulate) restoration. Results of this paper can be utilized by stakeholders to estimate and examine the potential of detention to provide hydrologic and chemical (particulate) from snow impacted by urban anthropogenic environs and activities.

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