Hydrologic Response of a Montane Meadow from Conifer Removal and Upslope Forest Thinning

This study evaluates the hydrologic response of restoration of a montane meadow by removal of encroached Pinus contorta and thinning of the adjacent forest. It is now a follow-up with four years of post-restoration data, on a previous analysis of a hydrologic response of the same meadow one year following restoration. A hydrologic change was evaluated through a statistical comparison of soil moisture and depth to groundwater between the restored Marian Meadow and a Control Meadow. Meadow water budgets and durations of water table depths during the growing season were evaluated. The four years following restoration of Marian Meadow had an increase in volumetric soil moisture during the wet season, but decreased soil moisture during the dry season. An average decrease in depth to groundwater of 0.15 m was found, which is consistent with the first-year post-restoration. The water budget confirms the first-year results that the hydrologic change following removal of encroached conifers was primarily due to a reduction of vegetation interception capture. There was no measurable difference in depth to groundwater or soil moisture following the upslope forest thinning likely due to the low level of forest removal with 2.8 m2/hectare reduction of the forest basal area. The cost of restoration to water gained was $0.69 USD/1000 L ($2.62 USD/1000 gal.)

Uncertainty in forest road hydrologic modeling and catchment scale assessment offorest road sediment yield

The goal of this study was to advance methods for assessment of forest road hydrologic response and sediment yield at a catchment scale. This research looked at the effect of soil depth estimation on the Distributive Hydrology Soil Vegetation Model (DHSVM), assessed the uncertainty and accuracy of hydrologic modeling of forest roads by DHSVM, and evaluated the use of road runoff and sediment sampling for catchment scale road sediment estimates. The influence of soil depth estimation on DHSVM varied by spatial scale and hydrologic process modeled. Soil depth measurement improved DHSVM simulated streamflow and road ditchflow for the rising limb of the hydrograph with no improvements during baseflow. For site specific or small scale modeling a deterministic soil depth model fit to field measurements was best. For larger scale simulations of streamflow mean soil depth provided as good or better estimates. Considerable uncertainty in estimates of road hydrologic response was observed from DHSVM. DHSVM over predicted individual road discharges. As the spatial scale and temporal scale was increased the uncertainty in DHSVM results decreased. This suggests that model structures chosen for DHSVM would be better determined with internal catchment data, at smaller scales. The GLUE assessment showed that change detection analysis with DHSVM will be limited to sites or scales of the catchment that behavioral model structures can be identified. From this research it was determined that only the catchment scale simulations and a few individual road locations could be used for change detection. The storm runoff volumes and peak flows from road ditchflow had linear relationships with storm sediment load. These relationships had to be developed by classes of road locations and types in an intensively managed forest due to variability in road design, hydrologic response, and road use. Sediment from roads estimated from field measurements used with SEDMODL2 or WARSEM provided substantially lower estimates than without field measured adjustments. The use of road runoff for sediment estimation provided even lower catchment scale sediment results. DHSVM simulated road runoff for sediment estimation provided catchment scale results similar to the sediment yield estimated from observed road runoff

Precipitation characteristics for landslide hazard assessment for the central Oregon Coast Range

Precipitation data from 1988-1995 for 13 rain gauges of the Department of Forest Engineering rain gauge network, and a longer precipitation record, 1976-1995, at Mapleton were analyzed. The objectives were to assess the spatial and temporal distribution of precipitation intensity and antecedent precipitation, and understand the role of these characteristics for triggering debris slides from headwalls in the central Oregon Coast Range. Frequency distribution curves and recurrence intervals using a partial-duration series were calculated for the maximum 5-minute, 30 minute, 1 hour, 2 hour, 6 hour precipitation durations and antecedent precipitation index (API) for the rain gauge network and the maximum 1 hour and 2 hour precipitation durations for Mapleton. Isohyet lines showing selected 2-year precipitation intensities and API were used to characterize the spatial distribution of precipitation intensity and API across the central Oregon Coast Range. The effect of elevation on this spatial distribution was investigated. An attempt to quantify the occurrence of high intensity precipitation occurring with high antecedent precipitation, which is hypothesized to trigger debris slides, was done by testing if the highest precipitation intensities (greater than a 1 -year recurrence interval) occurred during the storms with the highest API. API and precipitation intensity were tested for correlation to discern if a particular precipitation duration could be used to predict API, thus make it possible to use a precipitation intensity based threshold to assess the general hazard of landslides. Precipitation intensities associated with selected recurrence intervals vary considerably over the study area. Precipitation values for selected durations and recurrence intervals could vary as much as 50% or larger for selected rain gauge locations. Precipitation intensities are higher in the central portion of the study area, centered around the ridges of the Siuslaw River watershed, with decreasing intensity toward the northern and southern boundaries possibly due to topographic influences. Higher API values are found more frequent where the high precipitation intensity spatial trends exists. Relationships between short duration precipitation intensities with elevation, and API with elevation, within the rain gauge network could not be determined. No single precipitation intensity, including total storm precipitation, showed a strong positive correlation with high API for the entire rain gauge network. It appears that any attempts to predict the precipitation characteristics which trigger headwall failure by a precipitation intensity threshold in the central Oregon Coast Range is not possible. Attempts to assess the risk of headwall failure by high API may be possible. High precipitation intensities occurred with high antecedent precipitation conditions and they occur at the highest antecedent precipitation conditions

Assessing Stream-Aquifer Connectivity in a Coastal California Watershed

We report the results of field and laboratory investigations of stream-aquifer interactions in a watershed along the California coast to assess the impact of groundwater pumping for irrigation on stream flows. The methods used include subsurface sediment sampling using direct-push drilling, laboratory permeability and particle size analyses of sediment, piezometer installation and instrumentation, stream discharge and stage monitoring, pumping tests for aquifer characterization, resistivity surveys, and long-term passive monitoring of stream stage and groundwater levels. Spectral analysis of long-term water level data was used to assess correlation between stream and groundwater level time series data. The investigations revealed the presence of a thin low permeability silt-clay aquitard unit between the main aquifer and the stream. This suggested a three layer conceptual model of the subsurface comprising unconfined and confined aquifers separated by an aquitard layer. This was broadly confirmed by resistivity surveys and pumping tests, the latter of which indicated the occurrence of leakage across the aquitard. The aquitard was determined to be 2–3 orders of magnitude less permeable than the aquifer, which is indicative of weak stream-aquifer connectivity and was confirmed by spectral analysis of stream-aquifer water level time series. The results illustrate the importance of site-specific investigations and suggest that even in systems where the stream is not in direct hydraulic contact with the producing aquifer, long-term stream depletion can occur due to leakage across low permeability units. This has implications for management of stream flows, groundwater abstraction, and water resources management during prolonged periods of drought

Global sensitivity analysis in hydrological modeling: Review of concepts, methods, theoretical framework, and applications

Sensitivity analysis (SA) aims to identify the key parameters that affect model performance and it plays important roles in model parameterization, calibration, optimization, and uncertainty quantification. However, the increasing complexity of hydrological models means that a large number of parameters need to be estimated. To better understand how these complex models work, efficient SA methods should be applied before the application of hydrological modeling. This study provides a comprehensive review of global SA methods in the field of hydrological modeling. The common definitions of SA and the typical categories of SA methods are described. A wide variety of global SA methods have been introduced to provide a more efficient evaluation framework for hydrological modeling. We review, analyze, and categorize research into global SA methods and their applications, with an emphasis on the research accomplished in the hydrological modeling field. The advantages and disadvantages are also discussed and summarized. An application framework and the typical practical steps involved in SA for hydrological modeling are outlined. Further discussions cover several important and often overlooked topics, including the relationship between parameter identification, uncertainty analysis, and optimization in hydrological modeling, how to deal with correlated parameters, and time-varying SA. Finally, some conclusions and guidance recommendations on SA in hydrological modeling are provided, as well as a list of important future research directions that may facilitate more robust analyses when assessing hydrological modeling performance

Watershed Analysis Results for Mendocino Redwood Company Lands in Coastal Mendocino and Sonoma Counties

To assess the needs for conservation, restoration and condition of aquatic habitat within its land Mendocino Redwood Company (MRC) has been conducting watershed analysis. From watershed analysis completed to date, we estimate 73percent of the total sediment inputs over the last 30 to 40 years are road and skid trail associated. Of that percentage 30 percent is road and skid trail associated mass wasting, and 32 percent is road surface and point source erosion, the remaining 11percent is surface and point source erosion from skid trails. Hillslope mass wasting (not associated with roads or skid trails) represents 27 percent of the sediment inputs. Using controllable erosion as an indicator of future sediment yield, MRC estimates there is 2.2 million cubic yards of potential road sediment delivery to be controlled. Watershed analysis has provided insights into aquatic habitat functions within coastal Mendocino and Sonoma Counties. The following qualitative indices by percent of streams demonstrate the quality of habitat functions: “on target” indicates habitat conditions that meet published targets for well functioning conditions, “marginal” indicates functional habitat conditions but not at optimal levels, and “deficient” indicates low habitat functions with need for improvement. Instream large woody debris (LWD) condition is mainly marginal and deficient with few streams being on target: one percent on target, 35 percent marginal, 35 percent deficient, and 29 percent no data. Stream shade conditions are mainly on target to marginal with some streams being deficient: 29 percent on target, 35 percent marginal, 12 percent deficient, and 24 percent no data. Stream temperature conditions for salmonids are found to be: 58 percent on target, 18 percent marginal, and 24 percent deficient. Salmonid spawning habitats are predominantly on target and marginal (15 percent on target, 35 percent marginal, three percent deficient, 48 percent no data). Salmonid rearing and over-wintering habitats are mainly marginal and deficient, with few on target streams (rearing habitat: one percent on target, 39 percent marginal, 13 percent deficient, 48 percent no data; over-wintering: two percent on target, 37 percent marginal, 13 percent deficient, 48 percent no data). Generally speaking low LWD levels and high sediment inputs affecting rearing and overwintering habitat for salmonids are the primary issues that need improvement, to a lesser extent stream temperature and spawning habitat. MRC has developed policies for improvement of riparian conditions for long term LWD recruitment needs of stream habitat. In the short term MRC is promoting the restoration of LWD in streams to improve current conditions. Sediment inputs are dominated by road issues. MRC has committed to upgrading and modernizing its entire road network, a process that will take approximately 30 years. To date MRC has made substantial headway in addressing road erosion and aquatic habitat impacts. In the five years that MRC has owned this land; MRC has removed 11 salmonid migration barriers, decommissioned approximately 10 miles of streamside logging roads, and controlled at least 400,000 cubic yards of controllable erosion. Further, a comprehensive monitoring program will test whether the MRC policies and restoration efforts are improving aquatic habitat and resource conditions

Variability in effect of climate change on rain-on-snow peak flow events in a temperate climate

The frequency of rain-on-snow (ROS) hydrologic events, which produce high runoff volumes and lead to large-scale flooding and avalanching, are likely to change in the future as the types and timing of precipitation change. The relationship between ROS precipitation events and peak daily flow events P1-year return were examined for historical and future runoff affected by climate change within the Santiam River Basin, Oregon. Historical streamflow records and modeled historical and future streamflow projections were analyzed for three sites across three elevation zones defined by the dominant precipitation types; rain, rain and snow transition, and snow. The results illustrate that, across elevation zones, historical peak daily flows P1-year return have a high frequency (\u3e60%) of association with ROS. The historical association between peak daily flows and ROS is highest within the transient rain and snow elevation band (350–1100 m), with 80% and 100% of P1 and P5-year return peak flows associated with ROS, respectively. In a future with increased air temperature due to climate change, our results indicate that a decrease in the frequency of high peak flow ROS events will occur in the low and middle elevation zones while the frequency of ROS associated peak flows will increase in high elevation areas. The transition of winter precipitation from snow to rain is predicted to increase peak daily flow

Uncertainty in hydrologic modelling for estimating hydrologic response due to climate change (Santiam River, Oregon)

This paper explores the predicted hydrologic responses associated with the compounded error of cascading global circulation model (GCM) uncertainty through hydrologic model uncertainty due to climate change. A coupled groundwater and surface water flow model (GSFLOW) was used within the differential evolution adaptive metropolis (DREAM) uncertainty approach and combined with eight GCMs to investigate uncertainties in hydrologic predictions for three subbasins of varying hydrogeology within the Santiam River basin in Oregon, USA. Predictions of future hydrology in the Santiam River include increases in runoff in the fall and winter months and decreases in runoff for the spring and summer months. One-year peak flows were predicted to increase whereas 100-year peak flows were predicted to slightly decrease. The predicted 10-year 7-day low flow decreased in two subbasins with little groundwater influences but increased in another subbasin with substantial groundwater influences. Uncertainty in GCMs represented the majority of uncertainty in the analysis, accounting for an average deviation from the median of 66%. The uncertainty associated with use of GSFLOW produced only an 8% increase in the overall uncertainty of predicted responses compared to GCM uncertainty. This analysis demonstrates the value and limitations of cascading uncertainty from GCM use through uncertainty in the hydrologic model, offers insight into the interpretation and use of uncertainty estimates in water resources analysis, and illustrates the need for a fully nonstationary approach with respect to calibrating hydrologic models and transferring parameters across basins and time for climate change analyses