Rainfall threshold for hillslope outflow: an emergent property of flow pathway connectivity

Nonlinear relations between rain input and hillslope outflow are common observations in hillslope hydrology field studies. In this paper we use percolation theory to model the threshold relationship between rainfall amount and outflow and show that this nonlinear relationship may arise from simple linear processes at the smaller scale. When the rainfall amount exceeds a threshold value, the underlying elements become connected and water flows out of the base of the hillslope. The percolation approach shows how random variations in storage capacity and connectivity at the small spatial scale cause a threshold relationship between rainstorm amount and hillslope outflow. <br><br> As a test case, we applied percolation theory to the well characterized experimental hillslope at the Panola Mountain Research Watershed. Analysing the measured rainstorm events and the subsurface stormflow with percolation theory, we could determine the effect of bedrock permeability, spatial distribution of soil properties and initial water content within the hillslope. The measured variation in the relationship between rainstorm amount and subsurface flow could be reproduced by modelling the initial moisture deficit, the loss of free water to the bedrock, the limited size of the system and the connectivity that is a function of bedrock topography and existence of macropores. The values of the model parameters were in agreement with measured values of soil depth distribution and water saturation

The importance of surface controls on overland flow connectivity in semi-arid environments: results from a numerical experimental approach

In semi-arid environments, the characteristics of the land surface determine how rainfall is transformed into surface runoff and influences how this runoff moves from the hillslopes into river channels. Whether or not water reaches the river channel is determined by the hydrological connectivity. This paper uses a numerical experiment-based approach to systematically assess the effects of slope length, gradient, flow path convergence, infiltration rates and vegetation patterns on the generation and connectivity of runoff. The experiments were performed with the Connectivity of Runoff Model, 2D version distributed, physically based, hydrological model. The experiments presented are set within a semi-arid environment, characteristic of south-eastern Spain, which is subject to low frequency high rainfall intensity storm events. As a result, the dominant hydrological processes are infiltration excess runoff generation and surface flow dynamics. The results from the modelling experiments demonstrate that three surface factors are important in determining the form of the discharge hydrograph: the slope length, the slope gradient and the infiltration characteristics at the hillslope-channel connection. These factors are all related to the time required for generated runoff to reach an efficient flow channel, because once in this channel, the transmission losses significantly decrease. Because these factors are distributed across the landscape, they have a fundamental role in controlling the landscape hydrological response to storm events

Spatial organisation of groundwater dynamics and streamflow response from different hydropedological units in a montane catchment

Funding was provided by the Leibniz Association (SAW-2012-IGB 4167) within the International Leibniz Graduate School: Aquatic boundaries and linkages- Aqualink. We would like to thank the NRI staff for their help during field work.Peer reviewedPostprin

One-Dimensional Hairsine-Rose Erosion Model: Parameter Consistency for Soil Erosion in the Presence of Rainfall Splash

Process-based erosion modelling has proven to be an efficient tool for description and prediction of soil erosion and sediment transport. The one-dimensional Hairsine-Rose (HR) erosion model, which describes the time variation of suspended sediment concentration of multiple particle sizes, accounts for key soil erosion mechanisms: rainfall detachment, overland-flow entrainment and gravity deposition. In interrill erosion, it is known that raindrop splash is an important mechanism of sediment detachment and therefore of sediment delivery. In addition, studies have shown that the mass transported from a point source by raindrop splash decreases exponentially with radial distance and is controlled by drop characteristics and soil properties. Here we test experimentally and numerically the HR parameter consistency at different transversal widths for soil erosion in the presence of splash. To achieve this, soil erosion experiments were conducted using different configurations of the 2 m × 6 m EPFL erosion flume. The flume was divided into four identical smaller flumes, with different widths of 1 m, 0.5 m, and 2 × 0.25 m. Total sediment concentration and the concentrations for the individual size classes were measured. The experimental results indicate that raindrop splash dominated in the flumes having the larger widths (1 m and 0.5 m). This process generated a short time peak for all individual size classes. However, the effect of raindrop splash was less present in observed sediment concentrations of the collected data from the smaller width flumes (0.25 m). For these flumes, the detached sediment was controlled by the transversal width of the flume. An amount of detached sediment adhered to the barriers instead of being removed in the overland flow. Moreover, the experimental results showed that the boundary conditions affect the concentration of the mid-size and the larger particles. The one-dimensional Hairsine-Rose model was used to fit the integrated data and to provide parameter estimates for each flume. The analytical results agreed with the total sediment concentrations but not the measured sediment concentrations of all individual size classes. The observed sediment concentrations for the individual size classes could be predicted only when the initial sediment concentration was adjusted and a new calculation of the settling velocities was used. This new settling velocity calculation was conducted by taking the effect of raindrop splash on the deposition force of the particles into account

One-dimensional Hairsine-Rose Erosion Model: Parameter Consistency in the Presence of Rainfall Splash.

See the poste

Effect of climate change and mining on hydrological connectivity of surficial layers in the Athabasca Oil Sands Region

This is the peer reviewed version of the following article: Kompanizare M, Petrone RM, Shafii M, Robinson DT, Rooney RC. Effect of climate change and mining on hydrological connectivity of surficial layers in the Athabasca Oil Sands Region. Hydrological Processes. 2018;32:3698–3716. https://doi.org/10.1002/hyp.13292, which has been published in final form at https://doi.org/10.1002/hyp.13292. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.This research analyses the impact of climate change and surface mining activities on the hydrologic connectivity of surficial (soil and geological) layers located in a watershed in the Athabasca Oil Sands Region. Surface water and groundwater flow are simulated for the period 2014–2080 under four climate scenarios: median (M), double precipitation (DP), no change in precipitation (NP), and double temperature (DT) and with the assumption of no change in the extent of mine activities after 2013. The results demonstrate that the annual growing season duration is longer and snowmelt happens earlier in the year 2080. During the growing season, the daily proportion of connected hydrologic units (DPCUs) remains approximately the same in the future under the different climate scenarios. It appears that around 68% of watershed area, mostly in western and central eastern portions, will be frequently connected (annual proportion of connected days [APCD] ≥ 20%) in the future. This area remains hydrologically connected for more than 20–50% of the year. Results also show that mining areas are located in infrequently connected areas (APCD < 20%), where DPCU values are significantly lower than other areas. DPCUs in forestlands are more stable with a growing season, that is, ~15 days longer than in wetlands. Comparisons between hydrologic responses in 2016 and 2080 show that, in 2080, maximum snow depths are about 0.7 times smaller, evapotranspiration is ~0.05 mm higher, capillary soil moisture in DT and NP scenarios are 1.01–1.52 mm lower, and the ratio of precipitation to potential evapotranspiration is almost the same during the growing season. However, at the end of growing season, the ratio is ~1 unit less in 2080 in DT and NP scenarios. Results also demonstrate that thinner surficial geological layers in the mining areas (located mostly in downstream part of the watershed) lead to their lower hydrologic connectivities. Therefore, these areas are more vulnerable to mining activity impacts, and their hydrologic response under a changing climate should be considered in reclamation planning.Husky Energy (Rooney, Petrone, Robinson) || Natural Sciences and Engineering Research Council of Canada (HEAD3; Petrone

Toward improved prediction of the bedrock depth underneath hillslopes: Bayesian inference of the bottom‐up control hypothesis using high‐resolution topographic data

The depth to bedrock controls a myriad of processes by influencing subsurface flow paths, erosion rates, soil moisture, and water uptake by plant roots. As hillslope interiors are very difficult and costly to illuminate and access, the topography of the bedrock surface is largely unknown. This essay is concerned with the prediction of spatial patterns in the depth to bedrock (DTB) using high‐resolution topographic data, numerical modeling, and Bayesian analysis. Our DTB model builds on the bottom‐up control on fresh‐bedrock topography hypothesis of Rempe and Dietrich (2014) and includes a mass movement and bedrock‐valley morphology term to extent the usefulness and general applicability of the model. We reconcile the DTB model with field observations using Bayesian analysis with the DREAM algorithm. We investigate explicitly the benefits of using spatially distributed parameter values to account implicitly, and in a relatively simple way, for rock mass heterogeneities that are very difficult, if not impossible, to characterize adequately in the field. We illustrate our method using an artificial data set of bedrock depth observations and then evaluate our DTB model with real‐world data collected at the Papagaio river basin in Rio de Janeiro, Brazil. Our results demonstrate that the DTB model predicts accurately the observed bedrock depth data. The posterior mean DTB simulation is shown to be in good agreement with the measured data. The posterior prediction uncertainty of the DTB model can be propagated forward through hydromechanical models to derive probabilistic estimates of factors of safety.Key Points:We introduce an analytic formulation for the spatial distribution of the bedrock depthBayesian analysis reconciles our model with field data and quantifies prediction and parameter uncertaintyThe use of a distributed parameterization recognizes geologic heterogeneitiesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137555/1/wrcr22005.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137555/2/wrcr22005_am.pd