DOCSLIB.ORG

“Dealing with Natural Hazards” Module 2 Floods Flood-Producing

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
“Dealing with Natural Hazards” Module 2 Floods Flood-Producing Module 2 Floods Flood-producing processes Swiss Virtual Campus “Dealing with Natural Hazards” Module 2 Floods Flood-producing processes “Dealing with Natural Hazards and Risks” 1 Module 2 Floods Flood-producing processes CONTENTS INTRODUCTION.........................................................................................................3 THE MYSTERY OF STORM FLOW........................................................................3 PROCESSES GENERATING WATER DISCHARGE..........................................5 THE RIVER FLOW COMPONENTS ................................................................................5 PROCESSES GENERATING SURFACE FLOW ...............................................................6 VARIABLE SOURCE AREA CONCEPT...........................................................................8 PROCESSES GENERATING SUBSURFACE FLOW.........................................................9 PROCESSES GENERATING GROUNDWATER FLOW ...................................................11 THE RIVER FLOOD HYDROGRAPH...................................................................13 DOMINANT PROCESSES - SPACE AND TIME SCALES...............................14 BIBLIOGRAPHY AND INTERNET RESSOURCES...........................................16 Lausanne, le 26.11.2002 C. Picouet & A. Beney A. Musy EPFL / HYDRAM “Dealing with Natural Hazards and Risks” 2 Module 2 Floods Flood-producing processes Introduction Apart from the rare effects of Jökulhaups, ice jam, or dam failures, floods in most river basins are caused almost entirely by excessively heavy and/or excessively prolonged rainfall, or in areas of snow and ice accumulation, by periods of prolonged and/or intense melt. In each case the operative processes result in a large volume of water which, under certain conditions, produce more runoff than: i) an area can store or, ii) a stream can carry within its normal channel. This learning unit attempt to clarify the nature of this flood-producing processes - from Horton ideas to those of today - responding to the key question of what are the hydrological rainfall-runoff processes. This course will also examine the storm hydrograph and its main parameters (hydrograph peaks and lag time) and the importance of the spatial scale in determining the dominant flow generation mechanism. The mystery of storm flow For a long time, human beings have been wondering about the origin of streams. Further questions arose from the observation that rivers continue to flow even after rain has stopped. What feed the rivers? The first recorded theories on the origin of water and its natural cycle were postulated by the Greeks, who regarded water to be one of the four elements (along with earth, wind and fire). Their main concern was about the source of water flowing in rivers. They imagined that in addition to rains, rivers were fed from some sort of subterranean body of fresh water. Aristotle (384-322 BC) developed the fanciful notion that river flow resulted in part from the condensation of vapour of groundwaters, itself produced by the flux and desalinisation of seawater in the ground. This misunderstanding persisted through Roman times. When Roman civilization faded, there was literally no original thinking about natural phenomena for about the next 1500 years. Even the great Leonardo da Vinci (1452 - 1519) maintained the concept of a hydrological cycle in which underground veins of water rose from the sea to the mountains, where they issued forth as rivers. During this underground passage the salt was filtered out. Figure 1 illustrates a typical thought of Europeans during the 17th century. This concept and those of da Vinci were identical to some of the concepts put forth by Greeks. Even though these ideas look humorous in the modern view, at that time many scholars seriously believed and tried to prove them. “Dealing with Natural Hazards and Risks” 3 Module 2 Floods Flood-producing processes Figure. 1. Origin of streams (Kircher, 1678). Athanasius Kircher contended that water is transported from sea-bed through under-ground canals and stored in huge hollow spaces inside mountains, where streams originate. The first person to provide a correct written explanation of the hydrologic cycle was a Frenchman, Bernard Palissy (1510 - 1590). Pierre Perrault (1608- 1680), french physicist, made the first quantitative measurements of hydrologic phenomena. He measured the average annual rainfall over a small part of the upper Seine basin as well as the annual discharge of the river from that catchment. He found that rainfall was six times the amount that flowed in the Seine, thus proving that precipitation was more than enough to supply the water in the Seine. However, he thought that the springs were fed by the rivers and that in general there was little infiltration of rainwater into the ground. Further investigation of the rainfall - runoff cycle was made in France by Edmé Mariotte (1620 - 1684). He confirmed Perrault’s work on the Seine and studied also infiltration of rainwater into the basement of the Paris basin. He observed that infiltrating precipitation penetrated the pores of the earth and accumulated in underground reservoirs. Edmond Halley (1656 - 1742) the noted English astronomer made an important contribution to hydrology by studying evaporation. He concluded that there was sufficient water evaporating from the ocean to supply all of the rivers and springs on earth. In the 18th Century progress was made in utilizing the correct knowledge of the hydrologic cycle to develop ground water supplies. In the 19th Century with the progress in geology (development of a more comprehensive understanding of the relationship of ground water with the geological formations) and meteorology, the water hydrology begun as a modern science. With the 20th century and the new scientific measurements and theories, the debate about “mystery of storm flow” is related to the process of stormflow “Dealing with Natural Hazards and Risks” 4 Module 2 Floods Flood-producing processes generation. The two essential questions of modern hydrology are "what becomes the water of rains?" (Penmann, 1963) and "where does the water of the river come from?" (Hewlett, 1961). The aim of the next chapter is to describe general and modern theory relating to flow generating mechanisms, from Horton ideas (1933) - innovative at the time - to those of today which are based on preferential flows. Processes generating water discharge The river flow components Commonly, the river flow (river runoff) is the amount of three separate sources of runoff, which may, at a given time, occur separately or simultaneously with varying magnitude (Figure 2): Figure 2. Hydrologic movement of water beneath the Earth's surface. Water usually enters the surface as precipitation. When rain falls to the ground, some water flows along the land surface to streams or lakes (surface flow), some water evaporates into the atmosphere, some is taken up by plants, and some seeps into the ground. This water then percolates into the soil layer. Some of this water flows horizontally as subsurface flow. Water continuing to flow downward eventually reaches a permanent store of water known as groundwater. The groundwater movement is called groundwater flow. § Surface flow. If rainfall is not intercepted, it will evaporate, infiltrate or lie in depression storage. Surface runoff is the rainfall surplus that flows over the surface to the nearest stream channel. Surface flow is generally referred to as overland flow, and may occur as interrill overland flow (also known as sheet flow or sheet wash) or rill flow. § Subsurface flow (or interflow). The subsurface flow is the portion of infiltrated rainfall, which has not passed down to the water table, but that moves laterally through the upper soil horizons until reaches the stream channel. “Dealing with Natural Hazards and Risks” 5 Module 2 Floods Flood-producing processes § Groundwater flow (or baseflow). Groundwater flow is the portion of infiltrate water that reaches the water table and then discharges into the stream. Ground water is water held within the interconnected openings of saturated rock beneath the land surface. We can also mention direct precipitations on the surface of the river. However, this process is quite marginal, considering that the catchment’s surface concerned is generally very small. The contribution rises nevertheless when precipitations are long-lasting or when hydrological networks are composed of lakes and marshes. Snowmelt runoff can be added too to this list of sources; this specific process will be discuss in the section "Snow-melt and movement processes". Processes generating surface flow There are two basic concepts that explain the production of surface runoff during rainfall events. § Hortonian overland flow In 1933, a hydrologist named Horton proposed a process for stormflow generation, named the process of Hortonian overland flow later, using the concept of infiltration capacity and neglecting the interception processes (Figure 3). The soil’s infiltration capacity is defined as the maximum rate at which water can be absorbed by a given soil per unit area under given conditions. Figure 3. Hortonian Overland flow. Overland flow occurs when rainfall intensity exceeds the soil's infiltration capacity (Figure 4). This capacity, characterized by the soil’s infiltrability, is supposed to decrease exponentialy as a function of time until a constant value. In a homogeneous soil with a deep water table, this final constant
Load more

Recommended publications
  • Chapter 3. Hydrology
    3 Hydrology Robert R. Ziemer and Thomas E. Lisle Overview transient snow packs during rain on snow events. l Streamflow is highly variable in mountainous l Removal of trees, which consume water, areas of the Pacific coastal ecoregion. The tends to increase soil moisture and base stream- timing and variability of streamflow is strongly flow in summer when rates of evapotranspira- influenced by form of precipitation (e.g., rain- tion are high. These summertime effects tend to fall, snowmelt, or rain on snow). disappear within several years. Effects of tree l High variability in runoff processes limits removal on soil moisture in winter are minimal the ability to detect and predict human-caused because of high seasonal rainfall and reduced changes in streamflow. Changes in flow are usu- rates of evapotranspiration. ally associated with changes in other watershed l The rate of recovery from land use processes that may be of equal concern. Studies depends on the type of land use and on the of how land use affects watershed responses are hydrologic processes that are affected. thus likely to be most useful if they focus on how runoff processes are affected at the site of disturbance and how these effects, hydrologic Introduction or otherwise, are propagated downstream. l Land use and other site factors affecting Streamflow is an essential variable in under- flows have less effect on major floods and in standing the functioning of watersheds and large basins than on smaller peak flows and in associated ecosystems because it supplies the small basins. Land use is more likely to affect primary medium and source of energy for the streamflow during rain on snow events, which movement of water, sediment, organic mate- usuallv produce larger floods in much of the rial, nutrients, and thermal energy.
    [Show full text]
  • Subsurface Drainage Processes, by Elizabeth Keppeler, and David Brown
    Subsurface Drainage Processes and Management Impacts1 Elizabeth Keppeler2 and David Brown3 Abstract: Storm-induced streamflow in forested upland watersheds is linked to he hydrologic response of forested watersheds to rain events rainfall by transient, variably saturated flow through several different flow Toccurs through several interrelated flow processes. Soil surface paths. In the absence of exposed bedrock, shallow flow-restrictive layers, or conditions determine whether rainfall will run off as surface flow or compacted soil surfaces, virtually all of the infiltrated rainfall reaches the stream whether it will infiltrate and travel through the subsurface. as subsurface flow. Subsurface runoff can occur within micropores (voids between Infiltration capacities for soils in the coastal redwood region exceed soil grains), various types of macropores (structural voids between aggregates, plant and animal-induced biopores), and through fractures in weathered and maximum rainfall intensities common in the region. Exceptions consolidated bedrock. In addition to generating flow through the subsurface, occur in isolated areas where bedrock is exposed at the land surface. transient rain events can also cause large increases in fluid pressures within a More widespread are infiltration limitations resulting from soil hillslope. If pore pressures exceed stability limits of soils and shallow geologic compaction associated with road building, landings, and other materials, landslides and debris flows may result. Subsurface monitoring of constructed surfaces. Over the great majority of forested landscapes, pipeflows and pore pressures in unchanneled swales at North Fork Caspar Creek rainfall infiltrates into the soil and flows through the subsurface to in the Jackson Demonstration State Forest began in 1985. Four sites have been streams, rivers, and lakes.
    [Show full text]
  • Hydrogeologic Characterization and Methods Used in the Investigation of Karst Hydrology
    Hydrogeologic Characterization and Methods Used in the Investigation of Karst Hydrology By Charles J. Taylor and Earl A. Greene Chapter 3 of Field Techniques for Estimating Water Fluxes Between Surface Water and Ground Water Edited by Donald O. Rosenberry and James W. LaBaugh Techniques and Methods 4–D2 U.S. Department of the Interior U.S. Geological Survey Contents Introduction...................................................................................................................................................75 Hydrogeologic Characteristics of Karst ..........................................................................................77 Conduits and Springs .........................................................................................................................77 Karst Recharge....................................................................................................................................80 Karst Drainage Basins .......................................................................................................................81 Hydrogeologic Characterization ...............................................................................................................82 Area of the Karst Drainage Basin ....................................................................................................82 Allogenic Recharge and Conduit Carrying Capacity ....................................................................83 Matrix and Fracture System Hydraulic Conductivity ....................................................................83
    [Show full text]
  • Watershed Surface and Subsurface Spatial Intraflows Model
    Watershed Surface and Subsurface Spatial Intraflows Model Thomas E. Croley II1 and Chansheng He2 Abstract: We present new developments to the original, spatially lumped large basin runoff model ͑LBRM͒ of the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory. In addition to making it a two-dimensional, spatially distributed model, we modify it to allow routing flows between adjacent cells upper soil zones, lower soil zones, and groundwater zones. We modify the LBRM continuity equations for these additional flows and add corresponding corrector terms to the original solution equations. We derive the flow network from elevation and hydrography and the LBRM automatically arranges cell computations. We apply the newly modified LBRM to the Kalamazoo River watershed in Michigan and to the Maumee River watershed in Ohio. The simulations show that the Kalamazoo River has dominant groundwater storage, allowing delayed and sustained hydrologic responses to rainfall whereas the Maumee River lacks any significant groundwater storage, allowing a fast flashy response to rainfall. These results are characteristic of the study watersheds, indicating that the addition of subsurface intraflows in the model has improved watershed representation. DOI: 10.1061/͑ASCE͒1084-0699͑2006͒11:1͑12͒ CE Database subject headings: Hydrology; Watersheds; Parameters; Subsurface flow; Hydrologic models. Introduction representation of the flow cells comprising the watershed ͑Croley and He 2005͒ and applied it to the Kalamazoo watershed ͑Croley Effective management of the Great Lakes water resources et al. 2005͒. This involved changes to the model structure to apply requires better representation and simulation of the Great Lakes it to the microscale as well as organization of watershed cells and hydrological systems.
    [Show full text]
  • Interaction of Ground Water and Surface Water in Different Landscapes
    Interaction of Ground Water and Surface Water in Different Landscapes Ground water is present in virtually all perspective of the interaction of ground water and landscapes. The interaction of ground water with surface water in different landscapes, a conceptual surface water depends on the physiographic and landscape (Figure 2) is used as a reference. Some climatic setting of the landscape. For example, a common features of the interaction for various stream in a wet climate might receive ground-water parts of the conceptual landscape are described inflow, but a stream in an identical physiographic below. The five general types of terrain discussed setting in an arid climate might lose water to are mountainous, riverine, coastal, glacial and ground water. To provide a broad and unified dune, and karst. MOUNTAINOUS TERRAIN downslope quickly. In addition, some rock types The hydrology of mountainous terrain underlying soils may be highly weathered or (area M of the conceptual landscape, Figure 2) is characterized by highly variable precipitation and fractured and may transmit significant additional water movement over and through steep land amounts of flow through the subsurface. In some slopes. On mountain slopes, macropores created by settings this rapid flow of water results in hillside burrowing organisms and by decay of plant roots springs. have the capacity to transmit subsurface flow A general concept of water flow in moun- tainous terrain includes several pathways by which precipitation moves through the hillside to a stream (Figure 20). Between storm and snowmelt periods, streamflow is sustained by discharge from the ground-water system (Figure 20A). During intense storms, most water reaches streams very rapidly by partially saturating and flowing through the highly conductive soils.
    [Show full text]
  • Integrated Surface-Subsurface Water Flow Modelling of the Laxemar Area Application of the Hydrological Model ECOFLOW
    R-07-07 Integrated surface-subsurface water flow modelling of the Laxemar area Application of the hydrological model ECOFLOW Nikolay Sokrut, Kent Werner, Johan Holmén Golder Associates AB January 2007 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel and Waste Management Co Box 5864 SE-102 40 Stockholm Sweden Tel 08-459 84 00 +46 8 459 84 00 Fax 08-661 57 19 +46 8 661 57 19 CM Gruppen AB, Bromma, 2007 ISSN 1402-3091 Tänd ett lager: SKB Rapport R-07-07 P, R eller TR. Integrated surface-subsurface water flow modelling of the Laxemar area Application of the hydrological model ECOFLOW Nikolay Sokrut, Kent Werner, Johan Holmén Golder Associates AB January 2007 This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the authors and do not necessarily coincide with those of the client. A pdf version of this document can be downloaded from www.skb.se Abstract Since 2002, the Swedish Nuclear Fuel and Waste Management Co (SKB) performs site investigations in the Simpevarp area, for the siting of a deep geological repository for spent nuclear fuel. The site descriptive modelling includes conceptual and quantitative modelling of surface-subsurface water interactions, which are key inputs to safety assessment and environmental impact assessment. Such modelling is important also for planning of continued site investigations. In this report, the distributed hydrological model ECOFLOW is applied to the Laxemar subarea to test the ability of the model to simulate surface water and near-surface groundwater flow, and to illustrate ECOFLOW’s advantages and drawbacks.
    [Show full text]
  • Part 624, Chapter 10, Water Table Control
    United States Department of Part 624 Drainage Agriculture National Engineering Handbook Natural Resources Conservation Service Chapter 10 Water Table Control (210-VI-NEH, April 2001) Chapter 10 Water Table Control Part 624 National Engineering Handbook Issued April 2001 The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer. (210-VI-NEH, April 2001) Acknowledgments National Engineering Handbook Part 624, Chapter 10, Water Table Control, was prepared by Ken Twitty (retired) and John Rice (retired), drainage engineers, Natural Resources Conservation Service (NRCS), Fort Worth, Texas, and Lincoln, Nebraska respectively. It was prepared using as a foundation the publication Agricultural Water Table Management “A Guide for Eastern North Carolina,” May 1986, which was a joint effort of the USDA Soil Conservation Service, USDA Agriculture Research Service (ARS), the North Carolina Agriculture Extension Service and North Caro- lina Agricultural Research Service. Leadership and coordination was provided by Ronald L. Marlow, national water management engineer, NRCS Conservation Engineering Division, Washington, DC, and Richard D.
    [Show full text]
  • Geomorphology, Hydrology, and Ecology of Great Basin Meadow Complexes
    Chapter 4: Hydrologic Processes Influencing Meadow Ecosystems Mark L. Lord, David G. Jewett, Jerry R. Miller, Dru Germanoski, and Jeanne C. Chambers Introduction rates and paths. Most bedrock units have low permeability. Intrusive igneous rocks and metamorphic rocks generally he hydrologic regime exerts primary control on ripar- exhibit low permeability and act as barriers to groundwa- Tian meadow complexes and is strongly influenced by ter flow (Plume 1996; Maurer and others 2004). However, past and present geomorphic processes; biotic processes; highly fractured basalt, a volcanic rock, may have hydrau- and, in some cases, anthropogenic activities. Thus, it is es- lic conductivity values up to about 400 m/day. Sedimentary sential to understand not only the hydrologic processes that rocks have a wide range of permeabilities; at the high end, operate within meadow complexes but also the interac- some carbonate rocks with fractures widened by solution tions of meadow hydrology with other processes that affect have hydraulic conductivity values up to 1000 m/day (Maurer these ecosystems. Regional- and watershed-scale analyses and others 2004). Unconsolidated deposits are commonly of have contributed to the understanding and management of fluvial origin, and although their hydraulic conductivity is meadows. However, investigation of meadow-scale char- highly variable, it may be as high as 670 m/day. Faults can acteristics and processes have shown that local factors can differ in permeability from surrounding earth materials by override larger-scale influences and that some processes, es- up to several orders of magnitude. In general, faults in un- pecially those related to groundwater hydrology, cannot be consolidated materials restrict groundwater flow, and faults fully explained by topographically defined watershed-scale in bedrock enhance flow (Maurer and others 2004).
    [Show full text]
  • Excess Rainfall and Soil Loss Reductions As the Water Table Lowered
    6.1 Chapter 6. SUBSURFACE HYDROLOGY M.R. Savabi, R.W. Skaggs and C. A. Onstad 6.1 Introduction Root zone soil water redistribution is an important part of the WEPP model hydrology because 1) soil water content affects the subsequent rainfall/runoff events, 2) root zone soil water content is used in the interaction between soil water and plant growth, and 3) soil water content is used in residue decomposition. The objective of this chapter is to present subsurface lateral flow and the surface and subsurface drainage routines. The governing equations along with the assumptions and application criteria are discussed. Furthermore, WEPP hydrology was tested on a poorly drained soil with and without an artificial subsurface drainage system. The validation results are presented in this chapter. 6.1.1 Model Sensitivity To Water Table Fluctuation Sensitivity of WEPP runoff and erosion prediction to fluctuation of the water table on a silt loam soil is shown in Figures 6.1.1 and 6.1.2. The model was run using a hypothetical site with a silt loam . −1 soil, and a saturated hydraulic conductivity (ks)of13mm h . The rainfall depth assumed was 60 mm with a duration of 60 min. The water table depth was the only parameter changed between the runs. The model simulated excess rainfall and soil loss reductions as the water table lowered. Therefore, the results of the WEPP sensitivity analysis complement the quantitative studies of the effects of subsurface drainage on runoff and erosion by Istok and Kiling (1983). 50 Rainfall = 60 mm Duration = 1 hour 40 Silt Loam Soil Ks = 13 mm/hr porosity = 41% 30 20 10 Excess Rainfall (mm) 0 0 5 10 15 20 Water Table Depth (cm) Figure 6.1.1.
    [Show full text]
  • Simulating Coupled Surface–Subsurface Flows with Parflow V3
    Geosci. Model Dev., 13, 1373–1397, 2020 https://doi.org/10.5194/gmd-13-1373-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Simulating coupled surface–subsurface flows with ParFlow v3.5.0: capabilities, applications, and ongoing development of an open-source, massively parallel, integrated hydrologic model Benjamin N. O. Kuffour1, Nicholas B. Engdahl1, Carol S. Woodward2, Laura E. Condon3, Stefan Kollet4,5, and Reed M. Maxwell6 1Civil and Environmental Engineering, Washington State University, Pullman, WA, USA 2Center for Applied Scientific Computing, Lawrence Livermore National Laboratory, Livermore, CA, USA 3Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA 4Institute for Bio- and Geosciences, Agrosphere (IBG-3), Research Centre Jülich, Geoverbund ABC/J, Jülich, Germany 5Centre for High-Performance Scientific Computing in Terrestrial Systems, Geoverbund ABC/J, Jülich, Germany 6Integrated GroundWater Modeling Center and Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO, USA Correspondence: Benjamin N. O. Kuffour ([email protected]) Received: 14 July 2019 – Discussion started: 23 August 2019 Revised: 17 January 2020 – Accepted: 20 February 2020 – Published: 23 March 2020 Abstract. Surface flow and subsurface flow constitute a nat- geochemical reaction, land surface (e.g., the Common Land urally linked hydrologic continuum that has not tradition- Model), and atmospheric models to study the interactions ally been simulated in an integrated fashion. Recognizing among the subsurface, land surface, and atmosphere systems the interactions between these systems has encouraged the across different spatial scales. This overview focuses on the development of integrated hydrologic models (IHMs) capa- current capabilities of the code, the core simulation engine, ble of treating surface and subsurface systems as a single and the primary couplings of the subsurface model to other integrated resource.
    [Show full text]
  • Channel Water Balance and Exchange with Subsurface Flow Along a Mountain Headwater Stream in Montana, United States
    Channel water balance and exchange with subsurface flow along a mountain headwater stream in Montana, United States R. A. Payn,1.2 M. N. Gooseff,3 B. L. McGlynn,2 K. E. Bencala,4 and S. M. Wondze1l5 [1] Channel water balances of contiguous reaches along streams represent a poorly understood scale of stream-subsurface interaction. We measured reach water balances along a headwater stream in Montana, United States, during summer base flow recessions. Reach water balances were estimated from series of tracer tests in 13 consecutive reaches delineated evenly along a 2.6 km valley segment. For each reach, we estimated net change in discharge, gross hydrologic loss, and gross hydrologic gain from tracer dilution and mass recovery. Four series of tracer tests were performed during relatively high, intermediate, and low base flow conditions. The relative distribution of channel water along the stream was strongly related to a transition in valley structure, with a general increase in gross losses through the recession. During tracer tests at intermediate and low flows, there were frequent substantial losses of tracer mass (>10%) that could not be explained by net loss in flow over the reach, indicating that many of the study reaches were concurrently losing and gaining water. For example, one reach with little net change in discharge exchanged nearly 20% of upstream flow with gains and losses along the reach. These substantial bidirectional exchanges suggest that some channel interactions with subsurface flow paths were not measurable by net change in flow or transient storage of recovered tracer. Understanding bidirectional channel water balances in stream reaches along valleys is critical to an accurate assessment of stream solute fate and transport and to a full assessment of exchanges between the stream channel and surrounding subsurface.
    [Show full text]
  • The Effect of Stream Discharge on Hyporheic Exchange
    water Article The Effect of Stream Discharge on Hyporheic Exchange Brian Babak Mojarrad 1,* , Andrea Betterle 2,3 , Tanu Singh 4 , Carolina Olid 5 and Anders Wörman 1 1 Department of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, 114 28 Stockholm, Sweden 2 Department of Water Resources and Drinking Water, EAWAG Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland 3 Department ICEA and International Center for Hydrology “Dino Tonini”, University of Padova, 35100 Padua, Italy 4 School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B45 0AJ, UK 5 Climate Impacts Research Centre, Department of Ecology and Environmental Science, Umeå University, 98107 Abisko, Sweden * Correspondence: [email protected]; Tel.: +46-76-775-2405 Received: 24 June 2019; Accepted: 9 July 2019; Published: 12 July 2019 Abstract: Streambed morphology, streamflow dynamics, and the heterogeneity of streambed sediments critically controls the interaction between surface water and groundwater. The present study investigated the impact of different flow regimes on hyporheic exchange in a boreal stream in northern Sweden using experimental and numerical approaches. Low-, base-, and high-flow discharges were simulated by regulating the streamflow upstream in the study area, and temperature was used as the natural tracer to monitor the impact of the different flow discharges on hyporheic exchange fluxes in stretches of stream featuring gaining and losing conditions. A numerical model was developed using geomorphological and hydrological properties of the stream and was then used to perform a detailed analysis of the subsurface water flow. Additionally, the impact of heterogeneity in sediment permeability on hyporheic exchange fluxes was investigated.
    [Show full text]