Stream restoration designed specifically to enhance hyporheic processes has seldom been
contemplated. To gain experience with hyporheic restoration, an engineered streambed was built
using a gravel mixture formulated to mimic natural streambed composition, filling an over-excavated
channel to a minimum depth of 90 cm. Specially designed plunge-pool structures, built with subsurface
gravel extending down to 2.4 m, promoted greatly enhanced hyporheic circulation, path length, and
residence time. Hyporheic process enhancement was verified using intra-gravel temperature mapping
to document the distribution and strength of upwelling and downwelling zones, computation of
vertical water flux using diurnal streambed temperature patterns, estimation of hyporheic zone cross
section using sodium chloride tracer studies, and repeat measurements of streambed sand content
to document evolution of the engineered streambed over time. Results showed that vertical water
flux in the vicinity of plunge-pool structures was quite large, averaging 89 times the pre-construction
rate, and 17 times larger than maximum rates measured in a pristine stream in Idaho. Upwelling and
downwelling strengths in the constructed channel were larger and more spatially diverse than in the
control. Streambed sand content showed a variety of response over time, indicating that rapid return
to an embedded, impermeable state is not occurring.


For more information contact: Mike ‘Rocky’ Hrachovec at Natural Systems Design — Email: | Phone: (206) 480-1130

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