Meadow restoration efforts typically involve the modification of stream channels to re-establish hydrologic conditions necessary for the maintenance of native vegetation. To predict change in the distribution of common meadow plant species in response to meadow restoration, a hydrologic model was loosely coupled to a suite of individual plant species distribution models. The approach was tested on a well-documented meadow/stream restoration project on Bear Creek, a tributary to the Fall River in northeastern California, U.S.A. We developed a surface-water and groundwater hydrologic model for the meadow. Vegetation presence and absence data from 170 plots were combined with simulated water-table depth time series to develop habitat-suitability models for 11 herbaceous plant species. In each model, the habitat suitability is predicted as a function of growing-season, water-table depth, and range. The hydrologic model was used to simulate water-table depth time series for the pre- and post-restoration conditions. These results were used to predict the spatial distribution of habitat suitability for the 11 herbaceous plant species. Model results indicate that restoration changed water levels throughout the study area, extending well beyond the near-stream region. Model results also indicate an increase in the spatial distribution of suitable habitat for mesic vegetation and a concomitant decrease in the spatial distribution of suitable habitat for xeric vegetation. The methods utilized in this study could be used to improve setting of objective and performance measures in restoration projects in similar environments, in addition to providing a quantitative, science-based approach to guide riparian restoration and active revegetation efforts.

Loheide et al.(2009) proposed a conceptual framework describing the groundwater-ecosystem connection in wet meadows of the Sierra Nevada and Cascade Ranges. This framework, based on field observations and hydrologic modeling, provides an understanding of how groundwater flow processes, both within meadow aquifers and at the watershed scale, affect vegetation patterning in the meadow. In the models presented, meadows with higher hydraulic conductivity than the surrounding bedrock were considered.

Meadows of the Sierra Nevada and Cascade mountains of California, USA, support diverse and highly productive wet-meadow vegetation dominated by sedges, rushes, grasses, and other herbaceous species. These groundwater–dependent ecosystems rely on the persistence of a shallow water table throughout the dry summer. Case studies of Bear Creek, Last Chance, and Tuolumne meadow ecosystems are used to create a conceptual framework describing groundwater–ecosystem connections in this environment. The water requirements for wet-meadow vegetation at each site are represented as a water-table-depth hydrograph; however, these hydrographs were found to vary among sites. Causes of this variation include (1) differences in soil texture, which govern capillary effects and availability of vadose water and (2) elevation-controlled differences in climate that affect the phenology of the vegetation. The field observations show that spatial variation of water-table depth exerts strong control on vegetation composition and spatial patterning. Groundwater-flow modeling demonstrates that lower hydraulic-conductivity meadow sediments, higher groundwater-inflow rates, and a higher ratio of lateral to basal-groundwater inflow all encourage the persistence of a high water table and wet-meadow vegetation, particularly at the margin of the meadow, even in cases with moderate stream incision.

We examined the relationship between water-table elevations and plant community distributions in a hydrologically restored riparian meadow. The meadow, adjacent to Bear Creek in northeastern California, experienced hydrologic modification due to “pond and plug” stream restoration. Plant species composition and cover were sampled within 128 plots, and a hydrologic model was used to simulate a three-year time series of water-table for each plot. TWINSPAN was used to classify the vegetation into four community types:Eleocharis macrostachya / Eleocharis acicularis, Downingia bacigalupii / Psilocarphus brevissimus, Carex nebrascensis / Juncus balticus, andPoa pratensis / Bromus japonicus. Nonmetric multidimensional scaling was utilized to investigate the relationships between community types and hydrologic variables. Community types were distributed along the hydrologic gradient at reasonably similar positions to those found in previous studies; howeverCarex nebrascensis, a species frequently used as an indicator of shallow water tables, occurred at greater water-table depths than reported in other studies. The range of water-table depths in this meadow was greater than previously observed, presumably due to the higher temporal resolution of water-table measurements, in addition to the intermittent nature of stream flow in Bear Creek. This study provides an increased understanding of the ecology of meadow communities, and can be utilized for improved design and objective setting in future restoration projects.

Wet meadow ecosystems in the highly seasonal climate of the Sierra Nevada, CA, depend on groundwater throughout the dry summer growing season. Meadows in California that have been extensively studied will be used to demonstrate the influence of hydrologic processes on vegetation patterning. These examples will include data on vegetation compostition, water table depth, and remotely sensed images of vegetation patterning.

Geomorphic processes influence flood hazards in the lowland fluvial-tidal transition area near the Cosumnes River-Dry Creek-Mokelumne River Confluence, Central Valley, California. Anthropogenic changes in the inherently flood-prone floodplain, flood basin, and Delta Island landscape increase flood hazards. Levee construction and flow regulation influence floods, increasing risks in both agricultural and rapidly urbanizing areas. Effective flood management requires a landscape scale approach that addresses both fluvial and tidal processes and that accommodates current and potentially higher future flood magnitudes and sea levels.

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.

It has been estimated that over 90% of the tidal freshwater wetlands of the Sacramento-San Joaquin Delta region in California, USA, have been leveed, removing them from tidal and floodwater inundation. One alternative for restoration of tidal freshwater marsh ecosystems is to reconnect regions currently managed for agricultural purposes to the adjacent rivers and sloughs. Two elements of such restoration efforts that have not been adequately addressed are the impact that restoration efforts are likely to impose on flood stages, and the extent of various habitat types that may develop. This study tests the hypothesis that habitat restoration and flood mitigation can be compatible. MIKE 11, a one-dimensional, unsteady hydraulic model is used to evaluate the flood stage impacts of five restoration scenarios for the McCormack-Williamson Tract, located in the northern Sacramento-San Joaquin Delta of California, USA. In addition to quantifying flood impacts, model results are used to quantify the volume of tidal exchange, and integrated with GIS to quantify the potential areal extent of subtidal, intertidal, and supratidal habitat zones within the project. The results indicate that the restoration would provide a mosaic of habitat types, and have a minimal adverse impact upon flood stages during a range of flooding conditions.