Recent large-magnitude floods and their impact on valley-floor environments of northeastern Yellowstone

The Lamar River watershed of northeastern Yellowstone contains some of the most diverse and important habitat in the national park. Broad glacial valley floors feature grassland winter range for ungulates, riparian vegetation that provides food and cover for a variety of species, and alluvial channels that are requisite habitat for native fish. Rapid Neogene uplift and Quaternary climatic change have created a dynamic modern environment in which catastrophic processes exert a major influence on riverine–riparian ecosystems. Uplift and glacial erosion have generated high local relief and extensive cliffs of friable volcaniclastic bedrock. As a result, steep tributary basins produce voluminous runoff and sediment during intense precipitation and rapid snowmelt. Recent major floods on trunk streams deposited extensive overbank gravels that replaced loamy soils on flood plains and allowed conifers to colonize valley-floor meadows. Tree-ring dating identifies major floods in 1918, ca. 1873, and possibly ca. 1790. In 1996 and 1997, discharge during snowmelt runoff on Soda Butte Creek approached the 100-year flood estimated by regional techniques, with substantial local bank erosion and channel widening. Indirect estimates show that peak discharges in 1918 were approximately three times greater than in 1996, with similar duration and much greater flood plain impact. Nonetheless, 1918 peak discharge reconstructions fall well within the range of maximum recorded discharges in relation to basin area in the upper Yellowstone region. The 1873 and 1918 floods produced lasting impacts on the channel form and flood plain of Soda Butte Creek. Channels may still be locally enlarged from flood erosion, and net downcutting has occurred in some reaches, leaving the pre-1790 flood plain abandoned as a terrace. Gravelly overbank deposits raise flood-plain surfaces above levels of frequent inundation and are well drained, therefore flood-plain soils are drier. Noncohesive gravels also reduce bank stability and may have persistent effects on channel form. Overall, floods are part of a suite of catastrophic geomorphic processes that exert a very strong influence on landscape patterns and valley-floor ecosystems in northeastern Yellowstone.     

碎石桩—黄土复合地基的抗液化性状数值分析

用二维有限元方法对碎石桩－黄土复合地基的抗液化性状进行了计算和分析，为在黄土地区开展碎石桩处理方法提供了理论依据。     

论潜蚀和块体运动在河流袭夺中的主导作用─—河流袭夺作用机制与实例剖析

区域地壳隆升或地槽回返褶皱成山后，斜坡上出现平行状水系。随着河流的溯源侵蚀，分水岭后退，水系适应内外力条件演变成不同型式，并发生河流袭夺。导致河流发生袭夺的决定性原因，一是袭夺河的快速溯源侵蚀，二是位于分水岭反面的高位被袭夺河的河床下与古分水岭下潜蚀作用和块体运动。湔江支流之一海子河在早更新世末依次袭夺了古花园沟河（已消失）和古银厂沟河（原石亭江右支流）等河。     

Dimensionless critical shear stress evaluation from flume experiments using different gravel beds

Flume experiments were conducted using four different gravel beds (D₅₀ + 12–39 mm) and a range of marked particles (10–65 mm). The shear stresses were evaluated from friction velocities, when initial movement of marked particles occurred. Two kinds of equations were produced: first for the threshold of initial movement, and second for generalized movement. Equations of the type 0_c + a(D_i/D₅₀)^b, as proposed by Andrews (1983) are applicable even if the material is relatively well sorted. However, the values of a and b are lower (respectively 0·050 and -0·70) for initial movement. Generalized movement requires a higher shear stress (a + 0·068 and b + -0·80). D₉₀ of the bed material and y₀ (the bed roughness parameter) were also used as reference values in place of D₅₀. They produced lower values than in natural streams, mainly owing to the fact that the material used in the flume is better sorted: clusters are less well developed and the bed roughness is lower.     

Ice-collapse induced waves and graded gravel ridges on a Lake Beach

Ice collapsing into the waters of proglacial Briksdal Lake, western Norway, generates waves which rework shoreline sediments. Swash establishes graded gravel ridges sub-perpendicular to the shoreline, derived from material eroded by backwash. A terminal gravel bar at the lakeward limit of wave-induced transport marks the maximum depth of water surface waves.     

Overwash processes along a gravel beach in south-east Ireland

Recent overwashing, and to a more limited extent overtopping, has occurred on a gravel-dominated beach just west of Carnsore Point in south-east Ireland. At relatively low points swash excursions have breached the duneline and extensive gravel fans have formed on landward-facing slopes. Also, at interbreach positions, swash ramps have been built-up in front of previously eroding dune cliffs, allowing overtopping at heights of up to 5 m above MHWOST, spreading a veneer of sediment over the adjacent dune ridge. In both cases events appear to be preceded by erosion and backbeach sand and gravel deposition. Stratigraphic, textural and fabric analyses assist in identifying environmental conditions that prevailed during overwash throat and fan, and overtopping ramp, sedimentation.     

A re-examination of the evidence for a Plio-Pleistocene marine transgression on the Chiltern Hills. III. deposits

A petrological re-examination of the deposits that Wooldridge and Linton used as evidence for a Plio-Pleistocene marine transgression on the Chiltern Hills indicates that many are fluvial and some have been reworked in a periglacial climate. However, those from Little Heath and Rothamsted, Hertfordshire and Lane End, Buckinghamshire are confirmed as marine and Plio-Pleistocene. Subsidence during the Pleistocene is suggested by the northeasterly decline in height of the few truly marine deposits.     

Effects of gravel and sand mulches on dew deposition in the semiarid region of China

Information regarding dew deposition on the stone-covered surface is scarce. The effects of gravel and sand mulches on dew condensation were studied during the late summer and fall of 1999 in the semiarid loess region of China. The results indicated that there were significant difference in daily dew amount between gravel mulch, sand mulch and dry loess soil (control). The average dew amount for gravel mulch was 0.071 mm d⁻¹ with extreme 0.022 and 0.20 mm d⁻¹. The average values for sand mulch and dry loess soil was 0.12 and 0.15 mm d⁻¹, respectively. The minimum dew amount was 0.048 mm d⁻¹ for sand mulch and 0.071 mm d⁻¹ for dry loess soil, and the maximum dew amount was approximate 0.25 mm d⁻¹ for both treatments. The results suggest that surface stone mulch can reduce dew deposition as compared to sand and dry loess soil.     

An optimized use of limited ground based topographic data for river applications

A prime requirement for hydrological applications,such as sediment budgeting or numerical modelling,is that produced Digital Terrain Models(DTMs)accurately represent the shape of landforms,especially for river reaches where data are not homogeneous.DTM error is a function of data point measurement accuracy and density and also of the field survey strategy when limited amounts of data will be acquired.This paper aims to advance the importance of the field survey strategy for the specific,but common cases,where only limited topographic data will be available.This methodology is based on the idea that any feature can be properly described by a set of cross sections and breaklines describing both main and secondary directions of the flow.Then,a longitudinal linear interpolation can be applied to the defined homogeneous zones.This morphologically oriented(MO)method that includes data acquisition strategy and interpolation,was validated using a reference DTM derived from LiDAR measurements.An estimation of the uncertainties also is suggested based on the distance of the nearest point and the local slope using a geographically weighted regression.The proposed MO method is typically applicable to Alpine river reaches characterized by multiple channels that may always be underwater and not navigable such as an alternate bar system with secondary and transverse channels.     

Factors controlling stable oxygen,hydrogen and carbon isotope ratios in regional groundwater of the eastern United Arab Emirates (UAE)

Increasing groundwater salinity and depletion of the aquifers are major concerns in the UAE. Isotopes of oxygen, hydrogen, and carbon concentrations in groundwater were used to estimate evaporation loss using the isotopes of oxygen and hydrogen, and using a carbon isotope to trace inorganic carbon cycling in two main aquifers in the eastern part of the United Arab Emirates. The δD‐δ¹⁸O of groundwater samples plotted on a line given by: δD = 4 δ¹⁸O + 4 ·4 (r² = 0·4). In comparison, the local meteoric water line (LMWL) has been defined by the line: δD = 8 δ¹⁸O + 15. In order to better understand the system investigated, samples were separated into two groups based on the δD‐δ¹⁸O relationship. These are (1) samples that plot above the LMWL (δD = 6·1 δ¹⁸O + 12·4, r² = 0·8) and which are located predominantly in the north of the study area, and (2) samples that plot below the LMWL (δD = 5·6 δ¹⁸O + 6·2, r² = 0·8) and which are mostly distributed in the south. Slopes for both the groups are similar and lower than that for LMWL indicating potential evaporation of recharging water. However, the y‐intercept, which differs between the two groups, suggests evaporation of return flow and evapotranspiration in the unsaturated zone to be more significant in the south. This is attributed to intense agricultural activities in the region. Samples from the eastern Gravel Plain aquifer have δ¹³C and dissolved inorganic carbon (DIC) values in the range from ? 10 to 17‰, and 12–100 mg C/l, respectively, while the range for those from the Ophiolite aquifer is from ? 11 to ? 16.4‰, and 16–114 mg C/l respectively. This suggests the control of C‐3 and C‐4 plants on DIC formation, an observation supported by the range δ¹³C of soil organic matter (from ? 18·5 to ? 22·1‰.) Copyright © 2007 John Wiley & Sons, Ltd.