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Inverse weighted distance and regression nonexact techniques were evaluated for interpolating methods snow water equivalent (SWE) across the entire Colorado River Basin of the western United States. A 1-km spacing was used for the gridding of snow telemetry (SNOTEL) measurements for the years 1993, 1998, and 1999, which on average, represented higher than average, average, and lower than average snow years. Because of the terrain effects, the regression techniques (hypsometric elevation and multivariate physiographic parameter) were found to be superior to the weighted distance approaches (inverse distance weighting squared, and optimal power inverse distance weighting). A regression detrended inverse weighted distance...
Low-frequency (periodicities lower than 20 years) hydrologic variability in the western United States over the past 500 years is studied using available tree-ring reconstructions of Palmer Drought Severity Index (PDSI), streamflow, and climate indices. Leading rotated principal component (RPC) scores of a gridded tree-ring reconstruction of the PDSI from 1525 to 1975 are significantly correlated with indices representing large-scale climate variations from the Pacific and Atlantic Oceans. RPC1 (31%) is related to the influence of North Pacific sea surface temperature (SST) variations, indexed by the Pacific Decadal Oscillation (PDO). RPC2 (24%) is apparently related to North Atlantic SST variations, indexed by the...
Overbank flooding is recognized by hydrologists as a key process that drives hydrogeomorphic and ecological dynamics in mountain valleys. Beaver create dams that some ecologists have assumed may also drive riparian hydrologic processes, but empirical evidence is lacking. We examined the influence of two in�channel beaver dams and a 10 year flood event on surface inundation, groundwater levels, and flow patterns in a broad alluvial valley during the summers of 2002–2005. We studied a 1.5 km reach of the fourth�order Colorado River in Rocky Mountain National Park (RMNP), Colorado, USA. The beaver dams and ponds greatly enhanced the depth, extent, and duration of inundation associated with floods; they also elevate...
Streamflow disaggregation techniques are used to distribute a single aggregate flow value to multiple sites in both space and time while preserving distributional statistics (i.e., mean, variance, skewness, and maximum and minimum values) from observed data. A number of techniques exist for accomplishing this task through a variety of parametric and nonparametric approaches. However, most of these methods do not perform well for disaggregation to daily time scales. This is generally due to a mismatch between the parametric distributions appropriate for daily flows versus monthly or annual flows, the high dimension of the disaggregation problem, compounded uncertainty in parameter estimation for multistage approaches,...
High-elevation lakes in the western United States are sensitive to atmospheric deposition of sulfur and nitrogen due to fast hydrologic flushing rates, short growing seasons, an abundance of exposed bedrock, and a lack of well-developed soils. This sensitivity is reflected in the dilute chemistry of the lakes, which was documented in the U.S. Environmental Protection Agency's Western Lake Survey of 1985. Sixty-nine lakes in seven national parks sampled during the 1985 survey were resampled during fall 1999 to investigate possible decadal-scale changes in lake chemistry. In most lakes, SO4 concentrations were slightly lower in 1999 than in 1985, consistent with a regional decrease in precipitation SO4 concentrations...
The existence of an upper limit to the magnitude of floods in a region is a long-standing and controversial hypothesis in flood hydrology. Regional envelope curves encompassing maximum flood magnitudes stabilize with progressive increases in the areal coverage and period of observation (Wolman and Costa, 1984). However, the short lengths of conventional gaging records limit substantial advances in testing whether this stabilization is evidence of an upper limit. In the Colorado River basin there are 32,120 station years of gage data, but the average period at a gaging station is only 20 years, with most stations having less than 70 years of observation. Paleoflood magnitudes derived from sediments of large prehistoric...
Stream hydrology strongly affects the structure of aquatic communities. Changes to air temperature and precipitation driven by increased greenhouse gas concentrations are shifting timing and volume of streamflows potentially affecting these communities. The variable infiltration capacity (VIC) macroscale hydrologic model has been employed at regional scales to describe and forecast hydrologic changes but has been calibrated and applied mainly to large rivers. An important question is how well VIC runoff simulations serve to answer questions about hydrologic changes in smaller streams, which are important habitat for many fish species. To answer this question, we aggregated gridded VIC outputs within the drainage...
As multicentury records of natural hydrologic variability, tree ring reconstructions of streamflow have proven valuable in water resources planning and management. All previous reconstructions have used parametric methods, most often regression, to develop a model relating a set of tree ring data to a target hydrology. In this paper, we present the first development and application of a K nearest neighbor (KNN) nonparametric method to reconstruct naturalized annual streamflow ensembles from tree ring chronology data in the Upper Colorado River Basin region. The method is developed using tree ring chronologies from the period 1400?2005 and naturalized streamflow from the period 1906?2005 at the important Lees Ferry,...
Alpine/subalpine ecosystems in Rocky Mountain National Park may be sensitive to atmospherically derived acidic deposition. Two- and three-component hydrograph separation analyses and correlation analyses were performed for six basins to provide insight into streamflow generation during snowmelt and to assess basin sensitivity to acidic deposition. Three-component hydrograph separation results for five basins showed that streamflow contained from 42 to 57% direct snowmelt runoff, 37 to 54% subsurface water, and 4 to 13% direct rain runoff for the May through October 1994 study period. Subsurface contributions were 89% of total flow for the sixth basin. The reliability of hydrograph separation model assumptions was...
Soil texture is a key variable in the coupled relationship between climate, soil, and vegetation. This coupling and its dependence on soil texture are studied in this paper using analytical descriptions for soil moisture dynamics and the corresponding vegetation water stress. Results confirm the importance of soil texture in partitioning rainfall into the mean values of the water balance loss components, namely, evapotranspiration, leakage, and runoff, and in determining vegetation water stress for the vegetation and climatic regimes of the La Copita Research Area in Texas. Two separate mechanisms by which this sensitivity to soil texture can impact the ecological structure at La Copita are illustrated. First, dynamics...
Field data obtained on a nearly contiguous segment of the Colorado River in western Colorado and eastern Utah are used to examine the mechanisms driving downstream changes in channel geometry. Measurements characterizing the bank-full hydraulic geometry, bed material grain size, and average channel gradient were made at closely spaced intervals in 10 alluvial and quasi-alluvial reaches covering 260 km of the river. These data indicate that changes in surface and subsurface grain sizes are small in relation to the change in channel slope: over the full length of the study area, the median grain size of the surface sediment decreases by a factor of a little more than 2, whereas the average channel slope decreases...
We evaluate three metrics representing the drivers of channel change downstream from dams. A balance between changes in sediment supply and transport capacity identifies conditions of sediment deficit or surplus. A Shields number represents the competence of postdam flows and the potential for incision under conditions of sediment deficit. A ratio of postdam to predam flood discharge provides a metric for the scale and rate of channel change, especially width. The metrics are calculated for more than 4000 km of some of the major rivers in the western United States. More than 60% of these rivers are in sediment deficit, and only a few reaches are in sediment surplus. The sediment balance can be used to assess the...
The hydrologic importance of grazing is receiving increased attention on rangelands in the United States. The literature on this topic is fragmented. This paper explores the available literature for information useful in understanding the hydrologic impacts of grazing intensity as related primarily to infiltration and runoff. Generally, data relative to range condition are not adequate for evaluating hydrologic impacts. Data relating grazing intensity to infiltration rates are available, yet distinct limitations are evident. These limitations are discussed in terms of identifying future research needs. The greatest need appears to be a detailed definition of the long-term effects of grazing (by year and season)...
Groundwater brine seepage into the Dolores River in Paradox Valley, Colorado, increases the dissolved solids load of the Colorado River annually by ∼2.0 × 108 kg. To abate this natural contamination, the Bureau of Reclamation plans to pump ∼3540 m3/d of brine from 12 shallow wells located along the Dolores River. The brine, with a salinity of 250,000 mg/L, will be piped to the deepest (4.9 km) disposal well in the world and injected mainly into the Mississippian Leadville Limestone. Geochemical modeling indicates, and water-rock experiments confirm, that a huge mass of anhydrite (∼1.0 × 104 kg/d) likely will precipitate from the injected brine at downhole conditions of 120°C and 500...
Vegetation, particularly its dynamics, is the often-ignored linchpin of the land-surface hydrology. This work emphasizes the coupled nature of vegetation-water-energy dynamics by considering linkages at timescales that vary from hourly to interannual. A series of two papers is presented. A dynamic ecohydrological model [tRIBS + VEGGIE] is described in this paper. It reproduces essential water and energy processes over the complex topography of a river basin and links them to the basic plant life regulatory processes. The framework focuses on ecohydrology of semiarid environments exhibiting abundant input of solar energy but limiting soil water that correspondingly affects vegetation structure and organization. The...
The Colorado River in Marble and Grand Canyons displays evidence of annual supply limitation with respect to sand both prior to [Topping et al, this issue] and after the closure of Glen Canyon Dam in 1963. Systematic changes in bed elevation and systematic coupled changes in suspended-sand concentration and grain size result from this supply limitation. During floods, sand supply limitation either causes or modifies a lag between the time of maximum discharge and the time of either maximum or minimum (depending on reach geometry) bed elevation. If, at a cross section where the bed aggrades with increasing flow, the maximum bed elevation is observed to lead the peak or the receding limb of a flood, then this observed...
Snow-water equivalent (SWE) data measured at several hundred montane sites in the western United States are used to examine the historic effects of El Nino and La Nina events on seasonal snowpack evolution in the major subbasins in the Columbia and Colorado River systems. Results are used to predict annual runoff. In the Columbia River Basin, there is a general tendency for decreased SWE during El Nino years and increased SWE in La Nina years. However, the SWE anomalies for El Nino years are much less pronounced. This occurs in part because midlatitude circulation anomalies in El Nino years are located 35� east of those in La Nina years. This eastward shift is most evident in midwinter, at which time, SWE anomalies...
The atmospheric water balance over the upper Colorado River is evaluated twice daily for the seven winter seasons 1957?1963. The atmospheric water balance yields the exchange of water and water vapor at the earth-atmosphere interface through the observation of the spatial and time distributions and fluxes of water vapor in the atmosphere over the basin. The quantity precipitation minus evaporation is determined as a residual of the computation and is accumulated for daily and seasonal values. In addition, a natural period analysis is performed; the natural periods are delineated by homogeneity in the parameter precipitation minus evaporation. The dry periods are shown to exhibit a seasonal trend in evaporation rate...
We present a technique for providing seasonal ensemble streamflow forecasts at several locations simultaneously on a river network. The framework is an integration of two recent approaches: the nonparametric multimodel ensemble forecast technique and the nonparametric space-time disaggregation technique. The four main components of the proposed framework are as follows: (1) an index gauge streamflow is constructed as the sum of flows at all the desired spatial locations; (2) potential predictors of the spring season (April?July) streamflow at this index gauge are identified from the large-scale ocean-atmosphere-land system, including snow water equivalent; (3) the multimodel ensemble forecast approach is used to...
In the past decade, there has been a growing interest of dam safety officials to incorporate a risk-based analysis for design-flood hydrology. Extreme or rare floods, with probabilities in the range of about 10?3 to 10?7 chance of occurrence per year, are of continuing interest to the hydrologic and engineering communities for purposes of planning and design of structures such as dams [National Research Council, 1988]. The National Research Council stresses that as much information as possible about floods needs to be used for evaluation of the risk and consequences of any decision. A regional interdisciplinary paleoflood approach was developed to assist dam safety officials and floodplain managers in their assessments...