Recession Behavior Research Articles

Insight into heterogeneous karst catchment by the dynamical system approach

The hydrological process heterogeneity in karst catchments makes collecting sufficient information about the karst system properties extremely difficult. Consequently, the parameterization and application of currently available modeling approaches is highly uncertain in karst. We implemented a modified dynamical system approach and explored the possibilities to analyze, simulate and characterize karst springs and sinking streams in the heterogeneous Ljubljanica river catchment in Slovenia. The discharge sensitivity functions were used to simulate the hydrographs and identify the differences in the temporal dynamics of the discharge recession. Most of the derived karst springs and sinking streams discharge sensitivity functions express dual discharge recession behavior most likely controlled by the hydraulic conveyance characteristics of karst underground conduits. The implemented approach offers a high potential for advancement in karst hydrology by using basic discharge data for analyses of karst catchment characteristics and future planning of karst water resource management.

Flow recession behavior of preferential subsurface flow patterns with minimum energy dissipation

Abstract. Understanding the properties of preferential flow patterns is a major challenge in subsurface hydrology. Most of the theoretical approaches in this field stem from research on karst aquifers, where two or three distinct flow components with different timescales are typically considered. This study is based on a different concept: a continuous spatial variation in transmissivity and storativity over several orders of magnitude is assumed. The distribution and spatial pattern of these properties are derived from the concept of minimum energy dissipation. While the numerical simulation of such systems is challenging, it is found that a restriction to a dendritic flow pattern, similar to rivers at the surface, works well. It is also shown that spectral theory is useful for investigating the fundamental properties of such aquifers. As a main result, the long-term recession of the spring draining the aquifer during periods of drought becomes slower for large catchments. However, the dependence of the respective recession coefficient on catchment size is much weaker than for homogeneous aquifers. Concerning the short-term behavior after an instantaneous recharge event, strong deviations from the exponential recession of a linear reservoir are observed. In particular, it takes a considerable time span until the spring discharge reaches its peak. The order of magnitude of this rise time is one-seventh of the characteristic time of the aquifer. Despite the strong deviations from the linear reservoir at short time spans, the exponential component typically contributes more than 80 % to the total discharge. This fraction is much higher than expected for karst aquifers and even exceeds the fraction predicted for homogeneous aquifers.

Baseflow estimation based on a self-adaptive non-linear reservoir algorithm in a rainy watershed of eastern China

Accurate baseflow estimation is critical for water resources evaluation and management, and non-point source pollution quantification. Nonlinear reservoir algorithm (NRA) has been increasingly applied to baseflow separation because of its good approximation to the real groundwater discharge (commonly dominated by the unconfined aquifer) in most watersheds. However, in the rainy regions, large uncertainties may remain in the traditional NRA-separated baseflow sequences due to its empirical transition function for the rising limb of discharge process, and the evident variations of baseflow recession in the initial period of the falling limb caused by the disturbance from surface flow or rainfall events. To improve the reliability of baseflow separation, a self-adaptive non-linear reservoir algorithm (SA-NRA) was developed in this study based on the NRA, a self-adaptive groundwater discharge modified parameter, and the Particle Swarm Optimization algorithm (PSO). The validation of SA-NRA in a rainy watershed of eastern China showed that SA-NRA could be the approach to provide a goodness-of-fit for baseflow recession behaviors in the rainy regions. The traditional NRA and Eckhardt's two-parameter recursive digital filter (ERDF), calibrated (or validated) only with the pure baseflow recession data, can hardly provide reliable baseflow predictions for the non-pure baseflow recession periods (including the rising limb and the falling limb with surface flow or rainfall disturbance) due to the apparent variations of baseflow recession behavior. Therefore, more attentions should be paid to the uncertainties of baseflow separation for the non-pure baseflow recession periods in the rainy regions.

Novel Engineering Methodology for Decoupled Aerothermal Analysis of Hypersonic Atmospheric Entry Flows

Analyses of thermal protection system response to atmospheric entry are generally performed in a decoupled manner where some terms in the surface balance equations are simplified. In such an approach, surface fluxes are calculated using a fluid dynamics solution of the hypersonic flowfield. These are nondimensionalized for use by a material response code, where correction terms are applied to account for the missing physics. A new method is presented here that directly includes ablation physics, thus removing the need for correction models. This approach includes the diffusion processes of ablative species in the boundary layer and nonequilibrium surface chemistry. The new approach is compared to the heritage methodology using a trajectory designed to allow molecular dissociation and vibrational energy contribution. The new methodology predicts surface temperatures with the same qualitative trend, with the largest disagreements in areas of the trajectory where nonequilibrium effects are expected to occur. The solid ablation flux and subsequent recession behavior are consistently lower for the new method, but this discrepancy in surface thermochemistry can be decreased by adopting kinetic models with more aggressive oxidation mechanisms. It is found that a large difference in computed recession does not necessarily equate to the largest difference in heat shield sizing.

Upscaling Hillslope‐Scale Subsurface Flow to Inform Catchment‐Scale Recession Behavior

AbstractThe subsurface flow contribution to a basin hydrograph is often conceptualized as a single lumped reservoir parameterized by a power law function fit through the observed recession behavior of the basin. However, basins may be better represented as multiple independent subsurface hillslope reservoirs characterized with variable, transient recession behavior as a function of the time history of recharge. In this work, we unify the latter, more complex understanding of the subsurface with the large‐scale power law recession behavior convenient in hydrologic modeling applications. This unification is achieved by deriving upscaling relationships capable of converting simple metrics of basin hillslope topography into a signature basin response characterizing the subsurface‐flow‐induced recession from a single recharge event. Event superposition may then be used to simulate the application of a time series of recharge and a simple scaling relationship may be used to handle basins with homogeneous conductivity. The signature response is informed by numerical simulations of the hillslope‐storage Boussinesq equation for unconfined saturated flow through sloping hillslopes applied to 30 basins in the CAMELS database. The efficacy of the upscaled signature response in replicating numerical simulations in 50 CAMELS basins is demonstrated, as is the practical efficacy of the upscaling relationships for predicting transient recession in 17 of these basins. The upscaled signature response method thus provides a tool for hydrologic modelers to estimate transient recession parameters using the insights of subsurface flow modeling, although the predictions made by this method are unable to capture the full variability of observed recession behavior.

Impacts of seasonally frozen ground on streamflow recession in the Red River of the North Basin

AbstractThe projected rising temperatures due to climate change can alter the frozen ground's duration and thickness in the cold regions of the Northern Hemisphere, leading to changes in surface and subsurface contributions to streamflow. The initial step in understanding the impacts of the changing climate on the hydrologic response of the cold climate watersheds is to investigate the effects of the cold climate processes (e.g., freeze–thaw processes) on watershed response. However, complexities associated with the spatiotemporal data collection of cold climate processes have limited the capabilities of hydrologic models in simulating cold climate watershed responses. This study aims to evaluate the impacts of seasonally frozen soil on the streamflow recession in the Red River of the North Basin (RRB). To the best of our knowledge, this study is one of the first attempts to quantify the impacts of frozen soil on the storage‐discharge relationship of the RRB. We define a set of hypotheses to evaluate how cold climate processes influence the surface and subsurface flow paths and affect the linearity/non‐linearity of the storage‐discharge relationship in spring and summer. The results confirmed that the cold climate processes control the recession behavior of the RRB. It was found that the streamflow discharge is linearly related to the storage during spring, whereas during summer, the relationship was less linear. Statistical analyses revealed that the antecedent winter soil temperature and snowpack control the seasonal dynamics of hydrograph recession. Particularly, results indicated a more linear storage‐discharge relationship for antecedent winters characterized by colder soil temperatures and larger snowpack. These findings highlight the importance of the cold climate hydrologic processes in cold climate basins such as the RRB.

Hillslope-scale exploration of the relative contribution of base flow, seepage flow and overland flow to streamflow dynamics

Surface and subsurface flows interact at different spatial and temporal scales through the development of saturated areas occurring when the aquifer reaches the surface. While this interaction exerts a strong control in the partitioning of water between base flow, seepage flow and overland flow, its quantification remains a challenge. Here, we propose a novel modeling approach based on two equivalent hillslopes to capture spatial and temporal variabilities of the main processes. We calibrate their subsurface hydraulic properties based on the temporal dynamics of stream discharge. The model is tested on two pilot catchments located in Brittany (France). For both catchments, the model is successfully calibrated on 40 years of stream discharge data. The results demonstrate that contrasted hydraulic properties are required, with: (1) a relatively low conductive hillslope (conductivities between 3x10–8 m/s and 2x10–6 m/s) enhancing overland flows during recharge periods while also sustaining low flows in the late recession period through slow aquifer discharge, and (2) a highly diffusive hillslope (diffusivity between 5x10–3 m2/s and 3x10–1 m2/s) dominantly shaping the event- to seasonal-scale streamflow recession behavior. The strong contrast of the two hillslopes reveals the fundamental role of heterogeneity in controlling groundwater storage-discharge functions, ruling out any homogeneous equivalent at the catchment scale. Low flows appear to be a non-obvious combination of the contributions of the two hillslopes, the less diffusive hillslope catching up to the more conductive one by the end of the low flow period. Catchment-scale responses integrate complex interactions between recharge, groundwater and overland flows through the volume of subsurface storage and the extent of the saturated area.

Hydrolysis susceptibility and carbamate formation for a low moisture-absorbing, siloxane-modified cyanate ester resin matrix (TC410) material used for composite space applications

Siloxane-modified cyanate ester resins are ideal matrix materials for next-generation, high-precision composites used for radomes and satellite structures. They provide extremely low moisture uptake, excellent microcracking resistance, and protection from atomic radiation. However, cyanate ester resins have been shown to be susceptible to hydrolysis during cure, which may significantly impact both mechanical and thermal performance. In this investigation, we evaluate the cure kinetics and hydrolysis susceptibility of a siloxane-modified prepreg system (TC410/M55J). DSC tests verified that the Ea of polymerization for the TC410 system is 65 KJ/mol. Samples were also exposed to moisture during cure at several temperatures, and FTIR was used to follow changes in the carbonyl peak absorption intensity to compare the rate kinetics and activation energy for hydrolysis leading to carbamate formation (52 KJ/mol). DMA tests of composites exhibited significantly reduced Tg’s with increasing moisture levels during cure. TGA of these cured samples exhibited both a significant decrease in the onset of the thermal decomposition temperature as well as an increase in the relative degree of volatiles generated at low temperature. Flatwise tension strength tests showed a linear reduction in strength with decreasing Tg, at an equivalent trend to previous work on an M55J/RS3C system indicating a similar mechanism. However, the added margin provided from the higher initial FWT strength in the TC410 system allows for larger decreases in Tg before significant degradation occurs. Laminates manufactured on composite mandrels resulted in parts with larger decreases in the tool-side Tg of the part when compared to the bag-side Tg, with the differential depending on the initial moisture content of the tool. AFM was shown to selectively identify these carbamate-affected regions by showing that the recession behavior of these less cross-linked areas was greater than in areas where the resin was properly cured. Composites with increased carbamate formation resulted in increasing warpage of the part with elevated temperature exposure due to variations in stress relaxation. This effect should be considered when manufacturing precision, high-dimensional stability composite hardware.

Dynamic coevolution of baseflow and multiscale groundwater flow system during prolonged droughts

Field and numerical studies suggest that baseflow is composed of waters from a spectrum of groundwater flow paths termed the Groundwater Flow System (GWFS) – from shallow hillslope contributions to watershed-scale deep circulation originating in headwaters and discharging into lowland rivers. Here, we explore the evolution of the GWFS under prolonged droughts to understand its dynamics and multiscale nature, and to elucidate its role in baseflow generation and recession at the watershed scale. We consider three drought scenarios of varying severity and simulate groundwater flow in a 2-D cross-section of an idealized watershed with deep permeable bedrock, tracking the evolution of flow paths, baseflow, and residence times during the recession process. We find that baseflow generation at different drainage stages, and within different subwatersheds, is influenced distinctly by flow paths of different scales, depending on the relative strength of the flow paths and the position of the subwatersheds relative to the recharge/discharge zones of the deeper watershed-scale groundwater circulation. Despite having the same local relief, geology, and climate, baseflow from each subwatershed has a distinct recession behavior and time-dependent residence time distribution. Also, the hydraulic and transport characteristics of baseflow generation co-evolve and are strongly affected by the connection state of the water table to subwatersheds. These findings suggest that asynchrony and dissimilarity of baseflow generation from hillslopes under the impact of the watershed-scale groundwater flow, and interactions with local-scale and intermediate-scale groundwater flow, must be taken into account when interpreting baseflow recession data and building conceptual baseflow models at the watershed scale.

Thermal analysis of porous carbon ablator in atmospheric re-entry environment

Aerospace vehicles are exposed to a high temperature environment by aerodynamic heating during re-entry. A thermal protection system (TPS) such as ablator is required to protect the spacecraft from this environment. In previous studies, porous carbon ablator (hereafter denoted as PCA) composed of three-dimensional networked porous carbon (here after denoted as TNPC) substrate and resin with a low residual carbon ratio is fabricated. An experimental performance of PCA is performed by arc-jet test and recession behavior is evaluated. Although the experimental evaluation on TNPC and PCA have been conducted, analytical evaluation is not established well. In the present study, the heat conduction analysis of TNPC and PCA is performed by finite element method. Thermal and mechanical properties of TNPC and PCA is obtained by experiments. As a result, the analytical results are generally in agreement with the experimental values. From the obtained temperature distribution, the thermal stress distribution is also evaluated. The result suggests that the design of ablator for the decrease of not only heat conduction, but also internal stresses are required.

A comparative evaluation of automated recession extraction methods to determine the late-time recession characteristics of karst spring hydrographs

Recession Curve Analysis is a common method to characterize karstic aquifers and their discharge dynamics. Although this technique provides crucial information on quantifying system hydrodynamic properties, the manually selected recession curves analysis is neither a practical technique to cover all candidate recession curves, nor it allows extracting the entire hydrological diversity of the recession behavior. This study aimed to comparatively evaluate the applicability of automated recession selection procedures to the late-time recession analysis of karst spring hydrograph. For the comparative evaluation of the three automated recession extraction methods (Vogel Method, Brutsaert Method, and Aksoy and Wittenberg Method), we quantified the late-time recession parameters of spring hydrographs by combining three extraction methods with four recession analysis methods (Maillet, 1905; Boussinesq, 1904; Coutagne, 1948; and Wittenberg, 1999). By applying our experimental design into the five karst springs located in Austria, we identified the possible weaknesses of the automated recession extraction procedures for the late-time recession analysis for spring hydrographs. To explore the value of the karst spring’s physicochemical data (electrical conductivity and water temperature) as a completion data for the recession curve analysis, we carried out the hydro-chemograph analysis to examine the recession time and its duration. The research provides a research direction as to how the automated recession extraction procedures for the karst spring hydrographs could be improved by the physicochemical signatures of karst springs.

Use of an Efficient Proxy Solution for the Hillslope‐Storage Boussinesq Problem in Upscaling of Subsurface Stormflow

AbstractThe hillslope‐storage Boussinesq (hsB) equation is a modification of the one‐dimensional Boussinesq representation of saturated subsurface flow that accommodates the impact of converging and diverging flows resulting from a hillslope with nonconstant width. Here, a surrogate model, the hsB Proxy, is developed which closely emulates the results of high‐quality numerical solutions of the hsB to reproduce the drainage response of a wide range of wedge‐shaped hillslopes in response to a recharge time series at a fraction of the computational cost of a numerical solution and with minimal loss of fidelity. The efficacy of the Proxy in emulating the hsB response of a single hillslope and the aggregate response of a network of hillslopes is demonstrated. The Proxy applies to wedge‐shaped hillslopes with homogenous hydraulic conductivity under uniform recharge, with the expectation that these hillslopes may inform future investigations into the upscaling behavior that results in the known power‐law relationship between subsurface storage and outflow in a basin. The utility of the hsB as a tool for evaluating upscaling problems is demonstrated in two applications. First, the Proxy response is compared to the known basin‐scale recession behavior in the Panola Mountain Research Watershed, under both transient and steady‐state conditions. Second, the Proxy is applied to derive the single best effective hillslope in a basin. The Proxy is expected to be a useful tool for rapid simulation of subsurface flow from hillslopes for use in hydrological models and land surface schemes.

Effects of Thermal Cycle and Ultraviolet Radiation on 3D Printed Carbon Fiber/Polyether Ether Ketone Ablator

The extreme heating environment during re-entry requires an efficient heat shield to protect a spacecraft. The current method of manufacturing a heat shield is labor intensive. The application of 3D printing can reduce cost and manufacturing time and improve the quality of a heat shield. A 3D printed carbon fiber/polyether ether ketone (CF/PEEK) composite was proposed as a heat shield material. The aim was to develop a heat shield and the structural member as a single structure while maintaining the necessary recession resistance. Test samples were exposed to thermal cycles and ultraviolet (UV) radiation environment. Subsequently, a tensile test was performed to evaluate the effect of thermal cycle and UV radiation on the mechanical properties. The sample’s recession performance and temperature behavior were evaluated using an arc heated wind tunnel. Exposure to thermal cycle and UV radiation have limited effect on the mechanical properties, recession behavior and temperature behavior of 3D CF/PEEK. Results from the arc heating test showed an expansion of the sample surface and better recession resistance than other existing ablator materials. Overall, 3D CF/PEEK has excellent recession resistance while maintaining mechanical properties when exposed to high temperature, thermal cycle and UV radiation.

Climate Change May Increase the Drought Stress of Mesophytic Trees Downslope With Ongoing Forest Mesophication Under a History of Fire Suppression

In mountainous headwater catchments, downslope flow of subsurface water could buffer downslope forest communities from soil moisture stress during drought. Here we investigated changes in landscape-scale vegetation patterns at five forested headwater catchments in the Coweeta Hydrologic Laboratory in the southern Appalachians. We used a ca. 30-year Landsat Thematic Mapper (TM) image record of normalized difference vegetation index (NDVI), spanning a period of recorded warming since the mid-1970. We then, related spatial and temporal canopy patterns to seasonal water balance, streamflow recession behavior, and low flow dynamics from the long-term hydrologic records. All hydrologic metrics indicated increasing evapotranspiration, decreasing streamflow given precipitation, and potentially decreasing downslope subsidy at the watershed scale over time, especially during low-flow periods. Contrary to expectations, leaf area index (LAI) and basal area increased more upslope compared to downslope over time, coincident with warming. Trends in the ratio of NDVI in upslope and downslope topographic positions were also supported by long-term tree basal area increment, litterfall, and sap flux data in one of the reference watersheds. Mesophytic trees downslope appeared to respond more to frequent droughts and experience lower growth than xerophytic trees upslope, closely mediated by the isohydric/anisohydric continuum along hydrologic flow paths. Considering ongoing forest “mesophication” under a history of fire suppression across the eastern US deciduous forests, this study suggests that mesophytic trees downslope may be more vulnerable than xerophytic trees upslope under ongoing climate change due to an apparent dependence on upslope water subsidy.

Fractional governing equations of transient groundwater flow in unconfined aquifers with multi-fractional dimensions in fractional time

Abstract. In this study, a dimensionally consistent governing equation of transient unconfined groundwater flow in fractional time and multi-fractional space is developed. First, a fractional continuity equation for transient unconfined groundwater flow is developed in fractional time and space. For the equation of groundwater motion within a multi-fractional multidimensional unconfined aquifer, a previously developed dimensionally consistent equation for water flux in unsaturated/saturated porous media is combined with the Dupuit approximation to obtain an equation for groundwater motion in multi-fractional space in unconfined aquifers. Combining the fractional continuity and groundwater motion equations, the fractional governing equation of transient unconfined aquifer flow is then obtained. Finally, two numerical applications to unconfined aquifer groundwater flow are presented to show the skills of the proposed fractional governing equation. As shown in one of the numerical applications, the newly developed governing equation can produce heavy-tailed recession behavior in unconfined aquifer discharges.

An Empirical Reevaluation of Streamflow Recession Analysis at the Continental Scale

AbstractStreamflow recession analysis is a widely used hydrologic tool that uses readily available discharge measurements to estimate otherwise unmeasurable watershed‐scale properties, predict low flows, and parameterize many lumped hydrologic models. Traditional methods apply the simplifying assumptions of outflow from a Boussinesq aquifer, which predicts the slope of the recession curve relating streamflow to its derivative in log‐log space to decrease from early‐stage to late‐stage recession. However, this prediction has not been validated in actual watersheds. Also, recent studies have shown that slopes of observed recession events are often much greater than traditional methods that predict with data point clouds. We analyze recession behavior of 1,027 streams from across the continental United States for periods of 10 to 118 years, identifying over 155,000 individual recession events. We find that the average slope of observed recession events is greater than that of the point cloud for all streams. Further, recession slopes of observed events decrease with time in only 10% of cases and instead increase with time in 74% of cases. We identify only nine watersheds where observed streamflow behavior often conforms to the predictions of traditional recession analysis, each of which is arid and flat with low permeability. Analysis of our extensive empirical results with a regionalization of catchment hydrologic characteristics indicates that heterogeneity of subsurface flow paths increases the nonlinearity and convexity of observed recession, likely as a function of watershed memory. The practical implications of our analysis are that streamflow is more stable during periods of extended drought than generally predicted.

Revisiting the Hewlett and Hibbert (1963) Hillslope Drainage Experiment and Modeling Effects of Decadal Pedogenic Processes and Leaky Soil Boundary Conditions

AbstractSubsurface flow dominates water movement from hillslopes to streams in most forested headwater catchments. Hewlett and Hibbert (1963,https://doi.org/10.1029/JZ068i004p01081) constructed an idealized hillslope model (0.91 × 0.91 × 15.0 m; 21.8°) using reconstituted C horizon soil to investigate importance of interflow, a type of subsurface flow. They saturated the model, covered it to prevent evaporation, and allowed free drainage for 145 days. The resulting recession drainage curve suggested two phases: fast drainage of saturated soil in the first 1.5 days and then slow drainage of unsaturated soil. Hydrologists interpreted the latter as evidence interflow could sustain baseflow, even during extended drought. Since that experiment, typical forest vegetation grew in the model, providing root and litter inputs for 55 years. We removed all aboveground live biomass and repeated the experiment physically and numerically (HYDRUS‐2D), hypothesizing that pedogenesis would change the drainage curve and further elucidate the role of unsaturated flow from hillslopes. Contrary to this hypothesis, drainage curves in our twice‐repeated physical experiments and numerical simulation were unchanged for the first ~10 days, indicating pedogenesis and biological processes had not largely altered bulk hydraulic conductivities or soil moisture release characteristics. However, drainage unexpectedly ceased after about 2 weeks (14.3 ± 2.5 days), an order of magnitude sooner than in the original experiment, due to an apparent leak in the hillslope analogous to commonly observed bedrock fractures in natural systems. Thus, our results are a more natural recession behavior that highlight how incorporation of alternative hydrologic outputs can reduce drainage duration and volume from soils to baseflow.

Carbon fiber reinforced ultra-high temperature ceramic matrix composites: A review

Abstract Recent studies on carbon fiber-reinforced ultra-high temperature ceramic matrix (C/UHTC) composites fabricated by hot-pressing, chemical vapor infiltration, polymer impregnation and pyrolysis, and melt infiltration (MI) are reviewed. Various efforts have been made to improve these preparation processes and to combine two or more of these because they have both the advantages and disadvantages in terms of the processing time, operating temperature, and the porosity of the resulting C/UHTC composites. In addition, the parameters governing the fracture toughness, thermal conductivity, and recession behavior (in oxidizing environments) of these composites have been discussed. This review demonstrates that C/UHTC composites with Zr- or Hf-based UHTC matrices fabricated via MI are potential candidates for advanced heat-resistant structural materials.

The role of landscape properties, storage and evapotranspiration on variability in streamflow recessions in a boreal catchment

Streamflow recession analysis provides valuable insights into catchment functioning that can be related to runoff generation, storage retention and baseflow dynamics. As an integrated characteristic, recession analysis is particularly useful in catchment comparison studies to help explain drivers of spatial and temporal variability in hydrological behavior. Here, five years of hourly streamflow data from 14, partly nested, catchments within a 68 km2 boreal forest landscape in Northern Sweden were used to explore spatiotemporal variation in hydrological processes through recession analysis. The aim of this study was to better understand spatial variation in runoff generation and storage-discharge dynamics across the landscape, as well as the relation to landscape properties. Due to high collinearity between variables, partial least square regression was used to quantify the associations between recession characteristics and catchment properties, as well as to identify key variables controlling recession behavior. We analyzed recession characteristics using both an aggregated approach including all recession data and individual recession events. The analyses based on individual recession events, indicated that catchment topography, quantified by indices such as mean slope or elevation above the stream network, is a primary control on the recession behavior during relatively high flows, whereas catchment area gains importance when flows are relatively low. The proportion of sediment and deep soils also controlled recession behavior. Furthermore, we found that recession characteristics are influenced by both evapotranspiration (ET) and proxies of antecedent catchment storage, but that the patterns were different depending on catchment properties. ET was less influential in catchments with deeper soils and larger catchment area. Shifts in recession rates were primarily related to variation in storage, with faster streamflow recessions occurring during periods with low storage. The results demonstrate the influence of catchment properties on recession behavior, and we found great value in analyzing individual recession events for an increased understanding of spatial and temporal recession characteristics. When recession properties were lumped together, the relationships to catchment characteristics were obscured. This indicates the value of more detailed analyses, at least under the strongly seasonal hydroclimatic conditions of this site.

Effect of processing on high-velocity water vapor recession behavior of Yb-silicate environmental barrier coatings

The purpose of this research was to investigate the corrosion behavior of the low/high Yb2SiO5 containing Yb2Si2O7 coatings under high-velocity water vapor flow. To that end, Yb2Si2O7 and Si coatings were deposited by atmospheric plasma spraying on SiC substrates. The corrosion tests were performed in the burned natural gas under atmospheric pressure, with a gas flow velocity of 100 m/s at 1200 °C for 200 h. After the test, a 25 μm thick, porous corrosion layer at the surface of the Yb2Si2O7 rich coatings was found accompanied with a mass reduction, whereas samples with Yb2SiO5 rich coatings showed mass gain indicating the greater resistance of Yb2SiO5 against water vapor. A comparison of the Yb2Si2O7 rich coatings tested in this work and Yb2Si2O7 bulk samples tested in an earlier work at the same facility revealed significantly different recession rates. Possible mechanisms responsible for this distinct behavior are discussed in the manuscript.