Subsurface flow | EPFL Graph Search

Subsurface flow, in hydrology, is the flow of water beneath earth's surface as part of the water cycle. In the water cycle, when precipitation falls on the earth's land, some of the water flows on the surface forming streams and rivers. The remaining water, through infiltration, penetrates the soil traveling underground, hydrating the vadose zone soil, recharging aquifers, with the excess flowing in subsurface runoff. In hydrogeology it is measured by the Groundwater flow equation. Runoff Water flows from areas where the water table is higher to areas where it is lower. This flow can be either surface runoff in rivers and streams, or subsurface runoff infiltrating rocks and soil. The amount of runoff reaching surface and groundwater can vary significantly, depending on rainfall, soil moisture, permeability, groundwater storage, evaporation, upstream use, and whether or not the ground is frozen. The movement of subsurface water is determined largely by the water gradient, typ

Stream temperature modeling using fiber optic distributed temperature measurements in a sub-Saharan watershed, Burkina Faso

Malik Matthey

High spatial and temporal resolution water temperature measurements, using DTS, allow to model and to control stream temperature evolution in the Tambarga’s basin (Burkina Faso). A wireless sensor network recorded solar radiation, air temperature, air humidity, wind speed (among others) on different sites on Tambarga’s basin (B.F.) in 2009. These data are compiled and used as inputs to force the model and to assess simulated river temperatures in the basin. Local parameters as shade coefficient, stream bed heat losses as well as land coverage coefficient are estimated from on field knowledge. Purpose but also need for this study, stream discharge estimation in the Tambarga’s river is paramount. Discharges are formed by subsurface flow, groundwater flow and runoff during rain events. Assuming that all three water discharge components have a different thermal signature leads to imagine that they can be identified with the DTS optical fiber, once they reach the main stream. The inflow emplacements are referred to as springs in this study. Finally, although this study leads to significant results, the last sections propose the installation of some more measuring instruments for controlling and improving the model accuracy.

2010

The role of the hyporheic flow on sediment transport processes : an experimental approach using particle image velocimetry.

Christophe Ancey, Daniel Vito Papa, Gauthier Paul Daniel Marie Rousseau, Angeliki Sklivaniti

The study of river dynamics usually considers a turbulent stream on an impervious bed. However, it is known that part of the total discharge takes place through the erodible bed, especially for mountain rivers. This hyporheic flow (or subsurface flow) is likely to play an active role in the stability of the erodible bed. The question then arises: How does the hyporheic flow affect bed stability and thereby bed load transport? Monitoring hyporheic flow under natural conditions remains a key challenge. Laboratory experiments and new measurement techniques shed new light on this problem. Using PIV-LIF method (Particle Image Velocimetry - Laser Induced Fluorescence) we investigate hyporheic flows through erodible beds. The experiment is conducted in a 2-m-long and 6-cm-width flume with 2-mm-diameter glass beads and 4-mmdiameter natural pebbles under turbulent stream conditions. In parallel, we develop a simple analytical model that accounts for the interaction between the surface and subsurface flows at the bed interface. As the Reynolds number of the hyporheic flow is fairly high (10 to 100), inertia cannot be neglected. This leads us to use the Darcy-Forchheimer law instead of Darcy’s law to model hyporheic flows. We show that this model is consistent with the PIV-LIF experimental results. Moreover, the PIV-LIF data show that hyporheic flows modify the velocity profile and turbulence. Our measurements and empirical model emphasize the exchange processes in coarse-grained river for incipient sediment motion.

2017

Stream temperature modeling in mountainous environments

Aurélien Gallice

Stream temperature is one of the key variables affecting the habitat suitability of numerous aquatic species. Over the past decades, research efforts on this topic have concentrated on low-land rivers of North-America, whereas mountainous environments have received much less attention - above all in Europe. The present thesis introduces two new models for stream temperature prediction in Alpine watersheds. Both are tested over selected catchments in Switzerland, a mountainous country which presents the advantage of possessing a dense network of automatic stream temperature measurement stations. The first model is specifically designed to provide stream temperature estimates in ungauged catchments, so as to compensate for the scarcity of temperature measurement sites in mountainous environments. Its design is based on a new statistical approach. As opposed to standard statistical models, which are common to many disciplines, the present one aims at incorporating some of the physics controlling stream temperature in its own structure. Its formulation is derived from an analytical solution to the equation describing the energy balance of an entire stream network. Some terms of this solution cannot be readily determined based on data available at the regional scale; they are approximated using standard statistical techniques. The resulting model is statistical in nature, but includes elements of thermodynamic principles. Its accuracy is shown to be similar to the one of a standard statistical model, its root mean square error being 1.3°C at the monthly time scale. In virtue of its physical basis, the model can be used to investigate into more detail the factors controlling stream temperature at the regional scale, as shown through a simple example. The second model is intended to provide deterministic stream temperature predictions, to be used for example in climate change studies. It builds upon an existing physically-based model, which has been entirely written anew in order to clarify its structure and ease future developments. Conceived as an add-on to the spatially distributed snow model Alpine3D, it simulates the flows of both water and energy within the catchment, based on a semi-distributed approach. Some components of the model can be represented using various alternatives; for example, three different techniques are available to simulate the temperature of subsurface runoff. This flexibility allows the model to be tuned to the specific needs of each user, but also permits a more thorough assessment of the simulation uncertainty by comparing the predictions of the various alternatives. Evaluation of the model in a high alpine watershed indicates that hourly mean discharge is reproduced with a Nash-Sutcliffe efficiency (NSE) of 0.82, and hourly mean stream temperature with a NSE of 0.78. Both models are shown to contribute to a better understanding of stream temperature dynamics in Alpine environments. Future work involves further research on the structure of the statistical model, as well as the application of the deterministic model within the framework of climate change studies.

EPFL2016

Stream temperature modeling in mountainous environments

Aurélien Gallice

EPFL2016