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Hyporheic flow patterns in relation to large river floodplain attributes Journal
Citation:
FAULKNER, B. R., RENEEJ BROOKS, K. J. FORSHAY, AND S. P. CLINE. Hyporheic flow patterns in relation to large river floodplain attributes Journal. JOURNAL OF HYDROLOGY. Elsevier Science Ltd, New York, NY, 448-449:161-173, (2012).
Impact/Purpose:
Hyporehic flow plays a very substantial role in maintaining water quality and habitat of rivers and streams. Most studies on hyporheic flow are conducted in small headwater streams. As a result little is known about the extent and importance of hyporheic flow in large rivers, and how that process might have been constrained by revetments common in large river systems. This study uses well data from an unconstrained reach of the Willamette River to study the extent and magnitude of hyporheic flow in a dynamic anastomosing river with well developed point bars, meander scrolls, and alcoves. This area is more characteristic of the natural geomorphic conditions in the central portion of the Willamette Valley than in ares with revetments, and should give us an idea for the potential for hyporheic flow with revetment restoration. This study shows that hyporheic flow varies dramatically depending on moisture conditions. During the dry season, hyporheic flow was oriented along the floodplain elevation gradient and median steady-state residence times in small islands and bars were on the order of months. In the larger islands steady-state residence times were on the order of years. Water was traveling pathways that were 8200 m on average. In the wet season, flow was oriented laterally away from the river and quickly intercepted and returned to the surface water system in alcoves and cutoffs connected to the river, and recharge due to infiltration of precipitation prevented hyporheic flow through older island areas. In the younger islands, median steady-state residence times ranged from about 6 to 1600 days. Wet season pathlengths were much shorter, on the order of 200 m, but the volume of water moving through hyporheic pathways was an order of magnitude larger than during the dry seasons. The study demonstrates that hyporheic flow can be substantial in large anastomosing rivers. Restoring these flows in highly constrained large river systems could potentially improve river water quality.
Description:
Field-calibrated models of hyporheic flow have emphasized low-order headwater systems. In many cases, however, hyporheic flow in large lowland river floodplains may be an important contributor to ecosystem services such as maintenance of water quality and habitat. In this study, we used a network of shallow monitoring wells, Light Detection and Ranging (LiDAR), and continuous monitoring to parameterize and calibrate stochastic threedimensional ground water models for a 9.7 km2 (2400 acres) area along a naturally-meandering section of the Willamette River floodplain in Oregon. This large river floodplain is representative of other similar systems. Steadystate simulations were done representing the wet winter and dry summer seasons. During the dry season, hyporheic flow was oriented along the floodplain elevation gradient and median steady-state residence times in small islands and bars were on the order of months. In the larger islands steady-state residence times were on the order of years. In the wet season, flow was oriented laterally away from the river and quickly intercepted and returned to the surface water system in alcoves and cutoffs connected to the river, and recharge due to infiltration of precipitation prevented hyporheic flow through older island areas. In the younger islands, median steady-state residence times ranged from about 6.1×101 to 1.6×102 days. In the model domain overall, the steady-state dry season median pathline length was about 8.2×102 with a maximum length of about 5.7×103 m. For the wet season, the median was about 2.0×102 m with a maximum length of about 3.5×103 m. Wet season hyporheic water penetrated deeper into the lower permeability geologic units by an order of magnitude, as compared to the dry season. This was likely due to the absence of precipitation infiltration during the dry season. In some areas land managers may consider revetment removal as a means to convert channelized systems to more natural systems with shallower depths in the main channel, meander scrolls, and alcoves that can enhance hyporheic flow. The results of this study provide information on how such decisions may affect the extent of hyporheic flow that may occur as a large river returns to its natural geomorphological dynamics.