@article{tillinghast_hunt_jennings_d'arconte_2012, title={Increasing Stream Geomorphic Stability Using Storm Water Control Measures in a Densely Urbanized Watershed}, volume={17}, ISSN={["1943-5584"]}, DOI={10.1061/(asce)he.1943-5584.0000577}, abstractNote={This study used previously established unit critical discharges, annual allowable erosional hours, and annual allowable volume of eroded bed-load standards to evaluate two types of storm water control measures (SCMs): low-impact development (LID) practices and a large detention SCM (wet pond). Nine initial scenarios modeled in PC Storm Water Management Model (PCSWMM) incorporated different combinations of wet ponds, green roofs, rainwater harvesting systems, permeable pavement, and rain gardens to determine the best scenario for reducing stream erosion potential within a highly urbanized watershed in Chapel Hill, NC. The best-case scenario to reduce annual erosional hours and eroded bed load within the stream consisted of an aggressive utilization of LID practices in combination with an undersized wet pond. Although this scenario did not meet the annual erosional hour standard for rural reference streams, 0.35 h/ha/year, it did reduce erosional hours and eroded bed-load sediment by factors of 2.4 and 2.5, respectively, improving the existing condition. An alternative wet pond outlet structure that used two elevations of small drawdown orifices was explored to determine if current wet pond design practices could be improved to include stream stability. The new configuration provided a modest reduction in the number of erosional hours, a factor of 1.3, but increased the volume of eroded bed load by a factor of 1.2 when compared with the normal wet pond. However, adding widespread LID practices to the alternative outlet design reduced erosional hours and bed load transport by factors of 1.8 and 1.2, respectively, when compared with the normally configured wet pond. The failure to meet the erosional standards in all scenarios demonstrated the difficulty of requiring highly urbanized watersheds (60% impervious) to meet such strict stream protection measures.}, number={12}, journal={JOURNAL OF HYDROLOGIC ENGINEERING}, author={Tillinghast, E. D. and Hunt, W. F. and Jennings, G. D. and D'Arconte, Patricia}, year={2012}, month={Dec}, pages={1381–1388} }
 @article{tillinghast_hunt_jennings_2011, title={Stormwater control measure (SCM) design standards to limit stream erosion for Piedmont North Carolina}, volume={411}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2011.09.027}, abstractNote={This study evaluated the potential impacts of sub-bankfull flows produced by stormwater control measures (SCMs) on stream geomorphic stability. In part, design standards for SCMs include peak flow attenuation to maintain pre-development flow conditions to those of undeveloped watersheds or return urbanized, developed watersheds back to the pre-developed state. Most SCMs target lower frequency storms, usually the 2-and/or 10-year discharge events, but leave peak flows resulting from higher frequency storms uncontrolled. SCMs are possibly subjecting streams to longer and more frequent periods of erosion, increasing stream channel instability. The d65 substrate size, pattern, profile, and dimension of 33 reference stream cross-sections in Piedmont North Carolina were modeled using the continuous simulations program, SWMM, to develop (1) a unit critical discharge metric in L/s/ha, Qc = 0.0035(d65)1.5048, (2) allowable annual erosional hour standard, Log(AAEH) = −1.26Log(d65) + 1.21, and (3) allowable volume of eroded bedload standard, Log(AV) = −0.64(Qc) − 1.52, for watersheds containing SCMs discharging into surface waters. The unit critical discharge represents a threshold that, once exceeded, incipient motion of the d65 particle can occur. These standards represented benchmarks of stable, naturally eroding reference streams. Ninety-four percent of the unit critical discharges were less than the 2-year 24-h event, indicating the necessity of controlling higher frequency sub-bankfull flows. The standards were applied to an urbanized watershed (one sub-catchment containing a structural SCM and two sub-catchments without) in Raleigh, North Carolina. The unit critical discharge metric appeared to adequately represent urbanized stream geomorphic processes for the sub-catchment undergoing urbanization (4.5% difference) but not for the mature urbanized sub-catchments (47.5% and 68.8% difference). Depending on the long-term management goal of the unstable stream, this metric is not applicable for all urbanized watersheds due to the discrepancy between the field and calculated unit critical discharges. Standards developed from urbanized reference streams could possibly better represent SCMs in urbanized watersheds. All three sub-catchments failed to meet the erosional standards demonstrating the ability of the standards to predict unstable geomorphic processes in streams. The addition of a detention SCM (wet pond), in the urbanized sub-catchment extended the duration of erosive flows from 37 to 87 h/ha/yr, but reduced the estimated volume of eroded bedload from 1.81 to 0.99 m3/m/ha/yr when compared to uncontrolled urbanization (no wet pond). Alterations to the design of the wet pond, increased volume size and change in orifice diameter, were explored to see if erosional standards could be better met. This study demonstrated the effect of current SCM design standards on stream stability and why geomorphic processes of stream channels should be incorporated in SCM design standards.}, number={3-4}, journal={JOURNAL OF HYDROLOGY}, author={Tillinghast, E. D. and Hunt, W. F. and Jennings, G. D.}, year={2011}, month={Dec}, pages={185–196} }