# effect of flow-induced exchange in hyporheic zones on longitudinal transport of solutes

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Effect of Flow-Induced Exchange in Hyporheic Zones on Longitudinal Transport of Solutes in Streams and Rivers (2002) Anders Worman, Aaron Packman, Hakan Johansson, and Karin Jonsson Daniel Kramer. (2) Introduction Terms For Discussion. - PowerPoint PPT PresentationTRANSCRIPT

Effect of Flow-Induced Exchange in Hyporheic Zones on Longitudinal Transport of Solutes in Streams and Rivers(2002)

Anders Worman, Aaron Packman, Hakan Johansson, and Karin Jonsson

Daniel Kramer

(2) INTRODUCTIONTERMS FOR DISCUSSIONSolute (uptake, residence time, longitudinal transport, and spatial variation)Moment MethodsSolute Break-through CurvesPDF Probability Density FunctionLog Normal ProbabilityClosed Form Solutions

(3) PURPOSE OF STUDYEvaluation of Hyporheic Exchange Using SolutesTo Better Understand Transport and Storage of Solutes in StreamCompare to a theoretical solute model (i.e. Transient Storage Model) Coupled with a physically based flow-induced uptake model (i.e. Pumping Exchange)Compare against real measurement data as obtained for a 30 km reach of stream (Sava Brook) in Uppland County, Sweden

(4) EVALUATION STEPSReview Previous Model Approaches (Diffusive and First Order Exchange)Couple these solute mass flux assumptions with a Hyporheic exchange flux assumptionThis combination allows for a solute break-through curve to be developed.This can then give various residence times depending on mathematical approach for comparisoncouple a physically based representation of flow-induced uptake in the Hyporheic zone with a model for the longitudinal in-stream solute transport.

(5) THEORYEXCHANGE MODELSFirst order mass transfer relationshipsParameterization of all mechanisms governing mixing.VS.Diffusive processDoes not have a hydro mechanical mechanism entirely non-mechancial

(6) THEORYTRANSPORT OF SOLUTESControlled by:Exchange with neighboring Hyporheic zone/wetlandsSorption on to particle matterBiogeochemical reactions

Must understand these interactions for overall understanding of the transport and fate of nutrient, chemicals, contaminants, etc.

(7) THEORY -TRANSIENT STORAGE MODEL (TSM)Theory of Transport in Streams with Hyporheic Exchange includeFormulated as first order mass transfer and is defined by: Exchange coefficientStorage zone depthYields - Residence Time of SoluteFlow Direction (GW versus River)Slope GradientDiffusion

Problems include unrealistic/over-simplified: cannot account for natural variability and must use multiple exchange rates.

(8) THEORYBENEFIT OF MODELSProvide a simplified model with a mathematical framework.

(9) THEORYPROBLEMS WITH MODELS

Diffusion Model - Includes the order of magnitude differences between effective diffusive coefficients and molecular diffusion coefficients. Both models are crude representations oversimplified.Require reach specific data to be obtained costly and timely

(10) HYPORHEIC EXCHANGE ADVECTION PUMPING

(11) HYPORHEIC EXCHANGE SOLUTE MASS FLUX & HYPORHEIC EXCHANGE FLUXEquation 1 = Solute Mass FluxEquation 2 = Hyporheic Exchange FluxEquation 1 + Equation 2 = allow for solute breakthrough curves to beCalcd per input data of in-stream transport parameters and residence times THIS IS THE ADVECTION STORAGE PATH MODEL or ASP Model

(12) RESIDENCE TIME PDFSPumping Exchange Models Advection Storage Path Model (ASP)Approximate of flat surface and sinusoidal pressure variation.

Mean Depth Hyporheic Zone and Wavelength

(13) RESIDENCE TIME PDFLog Normal

Exponential

SimulatedALL Are Close to the Same General TimePump ModelTSM ModelAdvection Pump Model

(14) RESIDENCE TIME PDFSingle Flow Path ModelDifferent ModelsCan Be used to predict Different Transports

(15) CLOSED FORM SOLUTIONSDerivation revealed that T and F are controlling Factors (Eq 7 through 10)

(16) CLOSED FORM SOLUTIONS

(17) CLOSED FORM SOLUTIONSTemporal Moments can be expressed as co-efficients to T(Eq 12 through 15)

(18) SAVA BROOK EXPERIMENTTritium as main tracerInjected for 5.3 hours (how not really discussed?)Measured at 8 stations along 30 km stretch (no spatial indication?) Discharge increased along stretch by factor of 4.85Water depth and discharge fairly constantTook hydraulic conductivity measurements along river to provide plus minus 20% accuracy at a 95% confidence interval

(19) SAVA BROOK EXPERIMENT85 cross sections geometries definedSlug test at 3 and 7 cm along 4 to 5 verticals lines/locationsPerformed weighted average on these tests to get permeability

(20) SAVA BROOK EXPERIMENT

(21) SAVA BROOK EXPERIMENT

(22) SAVA BROOK EXPERIMENT

(23) SAVA BROOK EXPERIMENTOnce water enters it is retained in the hyporheic zone for a relatively long time

(24) MODEL VERSUS DATA POINTS

(25) MODEL VERSUS DATA POINTS

(26) EQUATING TO STATE VARIABLES Review of land type per state variables of a stream showed land use may control Hyporheic exchange - (through differences in channel morphology etc.)

(27) CONCLUSIONSThe ASP model which is transient combined with advection pumping predicted correctly when compared to Sava BrookTransient systems best generally analyzed by exponential PDFsAdvection flows tend to dominates Sava Brook and match well with Log-normal PDFs so best for streams with pump exchange Based on Froude number you could potentially analyze other streams - exchange rate increase and residence time decrease with decreasing Froude number.

(28) VARIABLESI am not sure if they ran monte-carlo simulations or just solved for the equations to find probability factors?Log normal vs exponential Why, is it because K is generally on a log scale and that is a major factor. Or because co-efficients of diffusion are exponential?

(29) QUESTIONS & MISSING DATA?Missing area description No real talk of geology, or location images and figuresSpecific maps of reach also missing, no spatial image of where measurements were takenLooking at graphs they need some legend work so I can identify what is what

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