Development of probability distributions for urban hydrologic model parameters and a Monte Carlo analysis of model sensitivity

This paper proposes an approach to estimating the uncertainty related to EPA Storm Water Management Model model parameters, percentage routed (P_R) and saturated hydraulic conductivity (K_sat), which are used to calculate stormwater runoff volumes. The methodology proposed in this paper addresses uncertainty through the development of probability distributions for urban hydrologic parameters through extensive calibration to observed flow data in the Philadelphia collection system. The established probability distributions are then applied to the Philadelphia Southeast district model through a Monte Carlo approach to estimate the uncertainty in prediction of combined sewer overflow volumes as related to hydrologic model parameter estimation. Understanding urban hydrology is critical to defining urban water resource problems. A variety of land use types within Philadelphia coupled with a history of cut and fill have resulted in a patchwork of urban fill and native soils. The complexity of urban hydrology can make model parameter estimation and defining model uncertainty a difficult task. The development of probability distributions for hydrologic parameters applied through Monte Carlo simulations provided a significant improvement in estimating model uncertainty over traditional model sensitivity analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Synergistic effects of water repellency and macropore flow on the hydraulic conductivity of a burned forest soil,south‐east Australia

Research shows that water repellency is a key hydraulic property that results in reduced infiltration rates in burned soils. However, more work is required in order to link the hydrological behaviour of water repellent soils to observed runoff responses at the plot and hillslope scale. This study used 5 M ethanol and water in disc infiltrometers to quantify the role of macropore flow and water repellency on spatial and temporal infiltration patterns in a burned soil at plot (<10 m²) scale in a wet eucalypt forest in south‐east Australia. In the first summer and winter after wildfire, an average of 70% and 60%, respectively, of the plot area was water repellent and did not contribute to infiltration. Macropores (r > 0·5 mm), comprising just 5·5% of the soil volume, contributed to 70% and 95%, respectively, of the field‐saturated and ponded hydraulic conductivity (K_p). Because flow occurred almost entirely via macropores in non‐repellent areas, this meant that less than 2·5% of the soil surface effectively contributed to infiltration. The hydraulic conductivity increased by a factor of up to 2·5 as the hydraulic head increased from 0 to 5 mm. Due to the synergistic effect of macropore flow and water repellency, the coefficient of variation (CV) in K_p was three times higher in the water‐repellent soil (CV = 175%) than under the simulated non‐repellent conditions (CV = 66%). The high spatial variability in K_p would act to reduce the effective infiltration rate during runoff generation at plot scale. Ponding, which tend to increase with increasing scale, activates flow through macropores and would raise the effective infiltration rates at larger scales. Field experiments designed to provide representative measurements of infiltration after fire in these systems must therefore consider both the inherent variability in hydraulic conductivity and the variability in infiltration caused by interactions between surface runoff and hydraulic conductivity. Copyright © 2010 John Wiley & Sons, Ltd.     

A coupled one‐dimensional viscoelastic–plastic model for aquitard consolidation caused by hydraulic head variations in aquifers

Accurate and practical calculation of aquitard consolidation is required for a reliable analysis of land subsidence caused by groundwater overexploitation in a multilayered aquifer system because aquitards are generally more compressible than aquifers are. This study proposes a coupled one‐dimensional viscoelastic–plastic consolidation model that considers the combined effect of changes in soil parameters and body force to simulate aquitard consolidation caused by hydraulic head variations in neighbouring aquifers. The proposed model uses variable total stress and simultaneously solves hydraulic head and vertical soil displacement. The constitutive relation based on the Voigt model with different elastic moduli of the spring in normally consolidated and overconsolidated soils is used to describe the viscoelastic–plastic deformation mechanism of aquitards. In addition, the proposed model considers the combined effect of variations in hydraulic conductivity, elastic moduli, and body force on the calculation of aquitard consolidation. Three hypothetical scenarios with various hydraulic head variations in aquifers are used to examine the coupled one‐dimensional viscoelastic–plastic consolidation model. The results show that neglecting plasticity and viscosity of soil causes aquitard consolidation to be respectively underestimated and overestimated. In addition, ignoring body force variation underestimates aquitard consolidation, whereas neglecting soil parameters variation overestimates aquitard consolidation. Two real case scenarios are also studied to further demonstrate the applicability of the coupled one‐dimensional viscoelastic–plastic consolidation model. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of frozen soil and snow cover on cold‐season soil water dynamics in Tokachi,Japan

Despite the potential impact of winter soil water movements in cold regions, relatively few field studies have investigated cold‐season hydrological processes that occur before spring‐onset of snowmelt infiltration. The contribution of soil water fluxes in winter to the annual water balance was evaluated over 5 years of field observations at an agricultural field in Tokachi, Hokkaido, Japan. In two of the winters, soil frost reached a maximum depth of 0·2 m (‘frozen’ winters), whereas soil frost was mostly absent during the remaining three winters (‘unfrozen’ winters). Significant infiltration of winter snowmelt water, to a depth exceeding 1·0 m, occurred during both frozen and unfrozen winters. Such infiltration ranged between 126 and 255 mm, representing 28–51% of total annual soil water fluxes. During frozen winters, a substantial quantity of water (ca 40 mm) was drawn from deeper layers into the 0–0·2 m topsoil layer when this froze. Under such conditions, the progression and regression of the freezing front, regulated by the thickness of snow cover, controlled the quantity of soil water flux below the frozen layer. During unfrozen winters, 13–62 mm of water infiltrated to a depth of 0·2 m, before the spring snowmelt. These results indicate the importance of correctly evaluating winter soil water movement in cold regions. Copyright © 2010 John Wiley & Sons, Ltd.     

A review of low‐cost space‐borne data for flood modelling: topography,flood extent and water level

During the last two decades, remote sensing data have led to tremendous progress in advancing flood inundation modelling. In particular, low‐cost space‐borne data can be invaluable for large‐scale flood studies in data‐scarce areas. Various satellite products yield valuable information such as land surface elevation, flood extent and water level, which could potentially contribute to various flood studies. An increasing number of research studies have been dedicated to exploring those low‐cost data towards building, calibration and evaluation, and remote‐sensed information assimilation into hydraulic models. This paper aims at reviewing these recent scientific efforts on the integration of low‐cost space‐borne remote sensing data with flood modelling. Potentials and limitations of those data in flood modelling are discussed. This paper also introduces the future satellite missions and anticipates their likely impacts in flood modelling. Copyright © 2015 John Wiley & Sons, Ltd.     

Hysteretic freezing characteristics of riparian peatlands in the Western Boreal Forest of Canada

Freezing characteristics were investigated for a sedge covered floating fen and spruce covered swamp located beside a shallow lake in the Western Boreal Forest of Canada. Thermal properties were measured in situ for one freeze‐thaw cycle, and for two freeze‐thaw cycles in laboratory columns. Thermal conductivity and liquid water content were related to a range of subsurface temperatures above and below the freezing thresholds, and clearly illustrate hysteresis between the freezing and thawing process. Thermal hysteresis occurs because of the large change in thermal conductivity between water and ice, high water content of the peat, and wide variation in pore sizes that govern ice formation. Field and laboratory results were combined to develop linear freezing functions, which were tested in a heat transfer model. For surface temperature boundary conditions, subsurface temperatures were simulated for the over‐winter period and compared with field measurements. Replication of the transient subsurface thermal regime required that freezing functions transition gradually from thawed to frozen state (spanning the ?0·25 to ?2 °C range) as opposed to a more abrupt step function. Subsurface temperatures indicate that the floating fen underwent complete phase change (from water to ice) and froze to approximately the same depth as lake ice thickness. Therefore, the floating fen peatland froze as a ‘shelf’ adjacent to the lake, whereas the spruce covered swamp had a higher capacity for thermal buffering, and subsurface freezing was both more gradual and limited in depth. These thermal properties, and the timing and duration of frozen state, are expected to control the interaction of water and nutrients between surface water and groundwater, which will be affected by changes in air temperature associated with global climate change. Copyright © 2009 John Wiley & Sons, Ltd.     

Geoelectrical structure and hydrogeological investigations of the southern Rif Cordillera (Morocco)

An electrical prospecting survey is conducted in the Rharb basin, a semi‐arid region in the southern part of the Rifean Cordillera (Morocco) to delineate characteristics of the aquifer and the groundwater affected by the marine intrusion related to Atlantic Ocean. Analysis and interpretations of electrical soundings, bi‐logarithmic diagrams and the geoelectrical sections highlight a monolayer aquifer in the southern part, a multilayer system in the northern part of the Rharb basin and lenticular semi‐permeable formations. Several electrical layers have been deduced from the analysis of bi‐logarithmic diagrams: resistant superficial level (R₀), conducting superficial level (C₀), resistant level (R), intermediary resistant level (R′), conducting level (Cp) and intermediary layer of resistivity (AT). Spatial distribution of the resistivity deduced from the interpretation of apparent resistivity maps (AB = 400 and 1000 m) and the decreasing of resistivity values (35–10 Ωm), in particular in the coastal zone show that this heterogeneity is related to several anomalies identified in the coastal area, which result from hydraulic and geological processes: (i) heterogeneous hydraulic conductivity in particular in the southern part of the Rharb; (ii) lateral facies and synsedimentary faulting and (iii) the relationship between the electrical conductivity and chloride concentration of groundwater shows that salinity is the most important factor controlling resistivity. The distribution of fresh/salt‐water zones and their variations in space along geoelectrical sections are established through converting subsurface depth‐resistivity models. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of rock fragment cover on hydrological processes under rainfall simulation in a semi‐arid region of China

Rock fragment cover has long been an important agricultural crop production technique on the Loess Plateau, China. Although this approach plays an important role in controlling hydrological processes and preventing soil erosion, inconsistent results have been recovered in this field. In this study, we investigated the effects of rock fragment cover on infiltration, run‐off, soil erosion, and hydraulic parameters using rainfall simulation in the field in a semi‐arid region of China. Two field plots encompassing 6 rock fragment coverages (0%, 10%, 20%, 25%, 30%, and 40%), as well as 2 rock fragment positions and sizes were exposed to rainfall at a particular intensity (60 mm h^?1). The results of this study showed that increasing the rock fragment coverage with rock fragments resting on the soil surface increased infiltration but decreased run‐off generation and sediment yield. A contrasting result was found, however, when rock fragments were partially embedded into the soil surface; in this case, a positive relationship between rock fragment coverage and run‐off rate as well as a nonmonotonic relationship with respect to soil loss rate was recovered. The size of rock fragments also exerted a positive effect on run‐off generation and sediment yield but had a negative effect on infiltration. At the same time, both mean flow velocity and Froude number decreased with increasing rock fragment coverage regardless of rock fragment position and size, whereas both Manning roughness and Darcy–Weisbach friction factor were positively correlated. Results show that stream power is the most sensitive hydraulic parameter affecting soil loss. Combined with variance analysis, we concluded that the order of significance of rock fragment cover variables was position followed by coverage and then size. We also quantitatively incorporated the effects of rock fragment cover on soil loss via the C and K factors in the Revised Universal Soil Loss Equation. Overall, this study will enable the development of more accurate modelling approaches and lead to a better understanding of hydrological processes under rock fragment cover conditions.     

Evaluation of seasonal patterns of hydraulic redistribution in a humid subtropical area,East China

Antecedent soil moisture or soil moisture status has a great impact on hydrological processes. Hydraulic redistribution (HR), a widely observed phenomenon, is defined as water distributed (typically at night) from moist soil to drier soil via plant roots, which plays an important role in soil moisture replenishment. Knowledge on seasonal patterns of HR and on the relationship between HR and soil water use is not fully understood. We investigated temporal variations in HR and total daily water use (Δθ) at stands of camphor and peach by monitoring soil moisture content in a humid region in eastern China. HR at the three locations reached its maximum values in summer (0.68 mm d⁻¹ to 1.15 mm d⁻¹) at depths of 15 cm and 35 cm. Redistributed water replenished 41% of water depleted in the soil at a 5–45-cm depth. Interestingly, normalized HR (i.e., HR/Δθ) showed a constant pattern during the growing season implying it is independent of seasonal climate alterations. This also indicated that HR had a stable effect on the replenishment of daily water use. Positive linear relationships between HR and Δθ were found at three measuring locations (camphor: R² = .35, p < .01; peach1: R² = .57, p < .01; peach2: R² = .63, p < .01), suggesting a relatively stable inherent linkage between HR and Δθ. This study suggested that hydrological processes involving soil moisture status or antecedent soil moisture, needs to take the HR effect into account across timescales from intraday to seasonal.     

Numerical modeling of hydraulic fracture propagation,closure and reopening using XFEM with application to in‐situ stress estimation

In this paper, a fully coupled model is developed for numerical modeling of hydraulic fracturing in partially saturated weak porous formations using the extended finite element method, which provides an effective means to simulate the coupled hydro‐mechanical processes occurring during hydraulic fracturing. The developed model is for short fractures where plane strain assumptions are valid. The propagation of the hydraulic fracture is governed by the cohesive crack model, which accounts for crack closure and reopening. The developed model allows for fluid flow within the open part of the crack and crack face contact resulting from fracture closure. To prevent the unphysical crack face interpenetration during the closing mode, the crack face contact or self‐contact condition is enforced using the penalty method. Along the open part of the crack, the leakage flux through the crack faces is obtained directly as a part of the solution without introducing any simplifying assumption. If the crack undergoes the closing mode, zero leakage flux condition is imposed along the contact zone. An application of the developed model is shown in numerical modeling of pump‐in/shut‐in test. It is illustrated that the developed model is able to capture the salient features bottomhole pressure/time records exhibit and can extract the confining stress perpendicular to the direction of the hydraulic fracture propagation from the fracture closure pressure. Copyright © 2016 John Wiley & Sons, Ltd.