Comparison of streambed texture and hydraulic conductivity between degraded, natural reference, enhanced, and restored streams in the New Hope Creek watershed in Durham, North Carolina

Critical links exist between stream channel attributes and water quality function within stream restorations. During the process of stream restoration, much attention goes into recreating the profile of natural reference stream channels, but far less attention is given to factors that affect characteristics of the hyporheic zone in restored streambeds. The Priority 1 restoration process typically requires filling in the existing unstable stream channel and creating a new channel in the adjacent floodplain. The restoration of urban streams is often confined spatially and economically, so one alternative method includes stream enhancements that occur entirely with the stream channel. For this analysis, six streams – two natural, one degraded, one enhanced, and two restored -- near Durham, North Carolina were selected for textural and hydraulic conductivity analysis to identify the potential for hyporheic functions within these different systems. While direct measurement of hyporheic exchange is a complex process that is often not feasible stream restoration evaluation, there are several relatively simple indicators of potential hyporheic exchange including soil texture and field permeameter measurements. The study seeks to answer two questions: (1) Is there a difference in streambed sediment texture between degraded, natural reference, enhanced, and Priority 1 restored streams and within the vertical profile of a streambed? (2) How does streambed hydraulic conductivity relate to sediment texture in a stream system? This analysis relates three main findings in relation to streambed sediment texture and permeability. First, twenty-five percent of the measured variation in hydraulic conductivity of a streambed is explained by clay. Second, Priority 1 restorations do initially lose permeability and potentially hyporheic functionality, and this may take around ten years to be recovered in a new channel. Third, despite a higher cost per linear foot in Priority 1 restorations, the additional benefits provided by this method could outweigh this initial expense. Streambed sediment texture is not the only factor in explaining hyporheic functionality, but is a key component to whether the hyporheic zone can exist. Managers should consider the texture of a new channel when restorations are completed as it may relate to how functionality will be regained in the system.