Stream restoration efforts, particularly within meadow systems, increasingly rely on “pond and plug” type methods in which (a) alluvial materials are excavated from the floodplain, forming ponds; (b) excavated alluvial materials are used to plug incised channels; and (c) smaller dimension channels are restored to the floodplain surface. Despite the large number of “pond and plug” restoration projects undertaken in the western United States, little research has been conducted to evaluate and quantify the effects of such topographic modification upon hydrology and riparian vegetation in these systems. To predict the changes in hydrologic processes and the distribution of commonly found meadow riparian plant species a hydrologic model and a suite of individual vegetation species models were used in concert. First we developed, calibrated and validated a hydrologic model of a 230 ha mountain meadow along a 3.6 km restored reach of Bear Creek in northeastern California, and used it to simulate the pre- and post-restoration topographic conditions. Next, vegetation data from 170 plot locations distributed throughout the study area were combined with simulated water table depth time series to develop species distribution models for individual plant species. In each vegetation model the probability of occurrence predicted as a function of growing season water table depth and range. Last, hydrologic and vegetation models were jointly used to predict the spatial distribution of individual plant species for pre- and post-restoration conditions. Our results document three general hydrologic responses to the meadow restoration effort: 1) increased groundwater levels and volume of subsurface storage; 2) increased frequency/duration of floodplain inundation and decreased magnitude of flood peaks; and 3) decreased annual runoff and duration of baseflow. Vegetation modeling results indicate an increase in the spatial distribution of obligate wetland, and facultative wetland plant species, as well as a decrease in the distribution of facultative upland and obligate upland plant species. This study supports and quantifies the hypothesis that “pond and plug” type stream restoration projects have the capacity to re-establish hydrologic processes necessary to sustain riparian systems. The methods utilized could be used to improve realistic objective setting in similar projects in similar environments, in addition to providing a quantitative, science-based approach to guide riparian restoration and active re-vegetation efforts.

Changes in sediment supply relative to transport capacity In .e,ravel-bed streams lead to adjustments in stream geomorphology. Dietrich et al. (1989) propose that when sediment supply is low relative to transport capacity, bed surface coarsening develops due to selective erosion of fines. They developed a dimensionless bedload transport rate (q*), which is the ratio between the sediment transport rate of the surface layer and the transport rate of material as fine as the subsurface or bedload. Flume experiments show that q* approaches unity when supply meets or exceeds capacity, and decreases in value when supply decreases. Longitudinal profiles and crosssection surveys on 7 km of the North Fork American River, CA show a downstream increase in supply relative to transport capacity. Q* values calculated from 15 sediment samples show corresponding increases downstream, indicating that the q* method may be useful for detecting trends in the supply-capacity relationship. Strong trends, however, were only seen when looking at the entire 7-km reach. On short reaches with limited data, absolute values of q* cannot be used for an accurate assessment of the supply-capacity relationship.

Managed baselevel lowering in tributaries that emerge from small canyons onto forested floodplains affects floodplain and fan sediment storage and small ephemeral tributary channel morphology in the Navarro River basin, Mendocino Country, California, USA. Numerous small tributaries (drainage areas up to several square kilometres) flow through culverts under Highway 128 across the forested floodplain of the Navarro River and one of its major tributaries, the North Fork. Excavation significantly deepened and widened these small tributaries upstream and downstream of culverts under the highway following the 1997 flood (recurrence interval 12 years), that inundated both the floodplain and the highway and culvert system. The excavation lowered the local baselevel of the tributary systems within the floodplain. This field study documents the effect of the lowered baselevel on floodplain and fan sediment storage and ephemeral tributary channel morphology. Excavation created defined channels in the floodplain where no channels previously existed. Additionally, the excavation and baselevel change created steps, or knickpoints, that migrated headward and incised the upstream tributary channels. Tributary incision decreases the sediment storage potential of the fan and floodplain and reduces the residence time for storage of fine sediment. A reduction in fine sediment residence time degrades downstream habitat for anadromous fish and other aquatic organisms in the Navarro River. Large wood influences floodplain and small tributary channel morphology by forming steps and increases sediment residence time by trapping sediment in forested tributary-fan-floodplain systems. Although this field investigation is specific to the Navarro River basin, our findings linking culvert maintenance excavation to geomorphic processes may be extended to other roads on forested floodplains in the Pacific Northwest or other systems with roads on floodplains.