A new approach to estimate canopy evaporation and canopy interception capacity from evapotranspiration and sap flow measurements during and following wetting

Canopy interception and its evaporation into the atmosphere during irrigation or a rainfall event are important in irrigation scheduling, but are challenging to estimate using conventional methods. This study introduces a new approach to estimate the canopy interception from measurements of actual total evapotranspiration (ET) using eddy covariance and estimation of the transpiration from measurements of sap flow. The measurements were conducted over a small‐scale sprinkler‐irrigated cotton field before, during and after sprinkler irrigation. Evaporation and sap flow dynamics during irrigation show that the total ET during irrigation increased significantly because of the evaporation of free intercepted water while transpiration was suppressed almost completely. The difference between actual ET and transpiration (sap flow) during and immediately following irrigation (post irrigation) represents the total canopy evaporation while the canopy interception capacity was calculated as the difference between actual ET and transpiration (sap flow) during drying (post irrigation) following cessation of the irrigation. The canopy evaporation of cotton canopy was calculated as 0.8 mm, and the interception capacity was estimated to be 0.31 mm of water. The measurement uncertainty in both the non‐dimensional ET and non‐dimensional sap flow was shown to be very low. Copyright © 2015 John Wiley & Sons, Ltd.     

Oxygen‐18 dynamics in precipitation and streamflow in a semi‐arid agricultural watershed,Eastern Washington,USA

Understanding flow pathways and mechanisms that generate streamflow is important to understanding agrochemical contamination in surface waters in agricultural watersheds. Two environmental tracers, δ¹⁸O and electrical conductivity (EC), were monitored in tile drainage (draining 12 ha) and stream water (draining nested catchments of 6‐5700 ha) from 2000 to 2008 in the semi‐arid agricultural Missouri Flat Creek (MFC) watershed, near Pullman Washington, USA. Tile drainage and streamflow generated in the watershed were found to have baseline δ¹⁸O value of ?14·7‰ (VSMOW) year round. Winter precipitation accounted for 67% of total annual precipitation and was found to dominate streamflow, tile drainage, and groundwater recharge. ‘Old’ and ‘new’ water partitioning in streamflow were not identifiable using δ¹⁸O, but seasonal shifts of nitrate‐corrected EC suggest that deep soil pathways primarily generated summer streamflow (mean EC 250 µS/cm) while shallow soil pathways dominated streamflow generation during winter (EC declining as low as 100 µS/cm). Using summer isotopic and EC excursions from tile drainage in larger catchment (4700‐5700 ha) stream waters, summer in‐stream evaporation fractions were estimated to be from 20% to 40%, with the greatest evaporation occurring from August to October. Seasonal watershed and environmental tracer dynamics in the MFC watershed appeared to be similar to those at larger watershed scales in the Palouse River basin. A 0·9‰ enrichment, in shallow groundwater drained to streams (tile drainage and soil seepage), of δ¹⁸O values from 2000 to 2008 may be evidence of altered precipitation conditions due to the Pacific Decadal Oscillation (PDO) in the Inland Northwest. Copyright © 2009 John Wiley & Sons, Ltd.     

The alluvial architecture of a suspended sediment dominated meandering river: the Río Bermejo,Argentina

The alluvial architecture of fine‐grained (silt‐bed) meandering rivers remains poorly understood in comparison to the extensive study given to sand‐bed and gravel‐bed channels. This paucity of knowledge stems, in part, from the difficulty of studying such modern rivers and deriving analogue information from which to inform facies models for ancient sediments. This paper employs a new technique, the parametric echosounder, to quantify the subsurface structure of the Río Bermejo, Argentina, which is a predominantly silt‐bed river with a large suspended sediment load. These results show that the parametric echosounder can provide high‐resolution (decimetre) subsurface imaging from fine‐grained rivers that is equivalent to the more commonly used ground‐penetrating radar that has been shown to work well in coarser‐grained rivers. Analysis of the data reveals that the alluvial architecture of the Río Bermejo is characterized by large‐scale inclined heterolithic stratification generated by point‐bar evolution, and associated large‐scale scour surfaces that result from channel migration. The small‐scale and medium‐scale structure of the sedimentary architecture is generated by vertical accretion deposits, bed sets associated with small bars, dunes and climbing ripples and the cut and fill from small cross‐bar channels. This style of alluvial architecture is very different from other modern fine‐grained rivers reported in the literature that emphasize the presence of oblique accretion. The Río Bermejo differs from these other rivers because it is much more active, with very high rates of bank erosion and channel migration. Modern examples of this type of highly active fine‐grained river have been reported rarely in the literature, although ancient examples are more prevalent and show similarities with the alluvial architecture of the Río Bermejo, which thus represents a useful analogue for their identification and interpretation. Although the full spectrum of the sedimentology of fine‐grained rivers has yet to be revealed, meandering rivers dominated by lateral or oblique accretion probably represent end members of such channels, with the specific style of sedimentation being controlled by grain size and sediment load characteristics.     

Identification of Uranyl Minerals Using Oxygen K‐Edge X‐Ray Absorption Spectroscopy

Although most of the world's uranium exists as pitchblende or uraninite, this mineral can be weathered to a great variety of secondary uranium minerals, most containing the uranyl cation. Anthropogenic uranium compounds can also react in the environment, leading to spatial–chemical alterations that could be useful for nuclear forensics analyses. Soft X‐ray absorption spectroscopy (XAS) has the advantages of being non‐destructive, element‐specific and sensitive to electronic and physical structure. The soft X‐ray probe can also be focused to a spot size on the order of tens of nanometres, providing chemical information with high spatial resolution. However, before XAS can be applied at high spatial resolution, it is necessary to find spectroscopic signatures for a variety of uranium compounds in the soft X‐ray spectral region. To that end, we collected the near edge X‐ray absorption fine structure (NEXAFS) spectra of a variety of common uranyl‐bearing minerals, including uranyl carbonates, oxyhydroxides, phosphates and silicates. We find that uranyl compounds can be distinguished by class (carbonate, oxyhydroxide, phosphate or silicate) based on their oxygen K‐edge absorption spectra. This work establishes a database of reference spectra for future spatially resolved analyses. We proceed to show scanning X‐ray transmission microscopy (STXM) data from a schoepite particle in the presence of an unknown contaminant.     

When hazard avoidance is not an option: lessons learned from monitoring the postdisaster Oso landslide,USA

On 22 March 2014, a massive, catastrophic landslide occurred near Oso, Washington, USA, sweeping more than 1 km across the adjacent valley flats and killing 43 people. For the following 5 weeks, hundreds of workers engaged in an exhaustive search, rescue, and recovery effort directly in the landslide runout path. These workers could not avoid the risks posed by additional large-scale slope collapses. In an effort to ensure worker safety, multiple agencies cooperated to swiftly deploy a monitoring and alerting system consisting of sensors, automated data processing and web-based display, along with defined communication protocols and clear calls to action for emergency management and search personnel. Guided by the principle that an accelerating landslide poses a greater threat than a steadily moving or stationary mass, the system was designed to detect ground motion and vibration using complementary monitoring techniques. Near real-time information was provided by continuous GPS, seismometers/geophones, and extensometers. This information was augmented by repeat-assessment techniques such as terrestrial and aerial laser scanning and time-lapse photography. Fortunately, no major additional landsliding occurred. However, we did detect small headscarp failures as well as slow movement of the remaining landslide mass with the monitoring system. This was an exceptional response situation and the lessons learned are applicable to other landslide disaster crises. They underscore the need for cogent landslide expertise and ready-to-deploy monitoring equipment, the value of using redundant monitoring techniques with distinct goals, the benefit of clearly defined communication protocols, and the importance of continued research into forecasting landslide behavior to allow timely warning.

     

Buckling of multi-segment underwater pressure hull

Results of a numerical and experimental study into buckling performance of multi-segment pressure hull subjected to uniform hydrostatic pressure are discussed. Constituents of multi-segment configurations are bowed-out cylindrical shells with, and without flanges. Details about five collapse tests of laboratory scale mild steel, CNC machined models are given. Segments were about 200 mm diameter, 100 mm long and had uniform wall thickness of 3 mm. Experimental collapse pressures were in the range from 12 to 20 MPa. Numerical collapse pressures agreed well with those obtained during experiments.