Connection between electrical resistivity and the hydraulic conductivity

Transkript

1 Connection between electrical resistivity and the hydraulic conductivity Ima Grabowski

2 Connection between electrical resistivity and the hydraulic conductivity Basic data from Föhr west and east water works with about 138 drilling profiles and resistivity logs. Graph. 1: Drillsites Föhr west Graph. 2: Drillsites Föhr east

3 We further used the SKY TEM model from the island Föhr from 2008 The resistivities clearly show a rough north/south seperation at a depth of -20 to -30m

4 We further used the SKY TEM model from the island Föhr from 2008 The resistivities clearly show a rough north/south seperation at a depth of -20 to -30m Northern Marschland Shows strong low Ohmic properties: High holocene clay content? Or Salt water intrusion? South west & east Is old Morain area with basicaly fresh water aquiveres

5 Is there a coherency between hydraulic conductivity and resistivity? Klasse T T,u/U,t U T/U,fs U,t,s,g RES Kf 1E Statistic frame work with the data set from the water works with ~ 138 drill sites and a classification Of 18 classes of the most common Soil and their Kf-values 6 U,s,g fs,u fs f-ms ms f-gs m-gs m-gs,g gs G,s

6 One example of first modus operandi, a borehole profile and log with estimated Kf-values: Kf [m/s] 5 x x 10-6

7 The mean of each of this 18 classes was taken and plotted against the Kf-values logarithmically scaled RES GN / Kf y = 41.93Ln(x) R 2 = RES Kf And we do have a correlation here

8 Ima`s Area Island Föhr Jenni`s area (Jennifer Klimke, 2011; Kompilation eines widerspruchsfreien geologisch geophysikalischen Modells für den Bereich der Grundwasserversalzungszone Quakenbrück in Niedersachsen. )

9 Comparison with Jenni`s work: Same statistic principal of classification at a study area in Niedersachsen We received a quite similar correlation of the two data sets! Imas & Jennis RES Werte Reihe1 Reihe Ohmm E-09 1E-08 1E Kf-Werte Jenni Klimke, 2011

10 taking an even closer look Archie: ρ Positive correlation: Resistivity and Kf AQUIFER 0,4 0,3 = ρ φ GROUNDWATER a φ m ρ Groundwater a= 1 m = 1.3 = 25Ωm [Ωm] Negative correlation : Porosity and Kf 0,2 0, Kf

11 We need to distinguish between: φ φ and total eff K f [ m/ s]

12 We are probably dealing with φ total in our statistic because we have the the positive correlation of Kf and resistivity but the negative correlation of Kf and porosity due to the fact that the geo-electrical Measurement is influenced by the total porosity and not by the effective porosity

13 But the statistics delivered us a regression equation G / witch enabled us to Build an iso-line plot of the study area Föhr. y = 41.93Ln(x) R 2 =

14 Conclusion: we managed to create an iso-line plot of Kf-values of our study area The more differentiated distribution of Kf-values in the subsurface could be used As input data in modelling -4

15 Conclusion Steps of process Borehole profiles Water works Föhr RES Petrography Kf estimated Classification 18 soil classes RES/Kf plotts Regression line & equation Transposing to x & feeding with SKY TEM data Surfer & GIS plott