Modeling the hydrologic effects of roadside ditch networks on receiving waters

Roadside drainage networks can affect deleterious changes to watershed hydrology and water quality. However, very few studies have explored these effects in agricultural settings where the potential for nonpoint source pollution and the implications of tighter hydrologic linkages between landscape and stream are more critical. In this study, we apply a GIS-based, spatially distributed hydrologic model under a variety of drainage scenarios to quantify the hydrologic effects of roadside ditches at multiple spatial scales. We also qualitatively investigate the relative impacts of ditches on phosphorus transport. Our principle findings indicate that roadside ditches: (i) substantially alter basin morphometry and natural flow pathways, (ii) increase peak and total event discharge and (iii) expedite the transport of agricultural pollutants, thereby short-circuiting natural degradation processes that would otherwise have mitigated their effects. These findings underscore how relatively fine-scale alterations to natural flow pathways can result in substantial impacts to watershed scale hydrology and water quality and may help to inform spatially-targeted water resource management decisions and future modeling efforts.