Dpt VII: Geological Survey of Belgium Royal Belgian Institute of Natural Sciences. Ground movements analysis in Brussels using the PSInSAR technique

Transcription

1 Dpt VII: Geological Survey of Belgium Royal Belgian Institute of Natural Sciences Ground movements analysis in Brussels using the PSInSAR technique Dr Xavier Devleeschouwer Terrafirma Workshop

2 Applications and examples of PSInSAR analysis in Belgium Processing based on 74 scenes used from 5 July 1992 to 19 November 2003 Brussels: - uplift along the Senne valley - subsidence in the Woluwe valley

3 Ground movements observed using PSInSAr data The IDW interpolation is based on the average annual velocity (mm/yr) of the PS selected in a surface of 900 km². Brussel A clear uplift is observed in the centre of Brussels along the Senne valley. A subsidence phenomenon occurs along the Dyle Valley between Ottignies and Wavre as well in Louvain-la-Neuve. Wavre

4 Uplift in the centre of Brussels revealed by PS data The IDW interpolation is based on the average annual velocity (mm/yr) of the PS in the centre of Brussels. Artesian wells and piezometers are localised on the map. Topographic map (1/ scale-map) of the National Geographic Institute constitutes the background image.

5 B A small part of the geological map of Brussels with the profile AB illustrated below. The profile is approximately oriented along the axis of the Senne river. Four aquifers are known: in the Quaternary sediments of the alluvial plain, in the Hannut Formation, in the Cretaceous and in the Cambrian basement. Note that the thickness of the Cretaceous increases towards the North. A A Quaternary B alluvial sediments (12-25 m) clays-sands (20-60 m) sand (upper) / clay (lower) chalk (few meters - >30 m) sandstones, quartzites and slates Cambrian Hannut Cretaceous Tertiary

6 2 1 Piezometers studied in Brussels 1 N of Brussels (Vilvoorde area) 2 center of Brussels 3 SE of Brusssels 3

7 1 Drie Fontein piezometer Gieterij piezometer Two piezometers in Vilvoorde related to the aquifer level of the Cretaceous.

8 Vilvoorde put Gieterij (nr ) X = Y = W & /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ m eting in m TAW data peilmetingen «Gieterij» Vilvoorde piezometer in the North of Brussels: an increase of 30 m of the piezometric level from 1991 till 2001 is observed in the Cretaceous aquifer

9 Vilvoorde put 3 Fonteinen (nr ) X = Y = W /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ /01/ meting TAW datum Same observations in the «3 Fonteinen» Vilvoorde piezometer (North of Brussels): an increase of 30 m of the piezometric level (from 1992 till 2000 is observed in the Cretaceous aquifer). An other increase of 20 m is recorded before the eighties. These observations implies a longer trend starting during the seventies of a 50 meters increasing trend.

10 19,57 m during 10 yrs 17,26 m during 12 yrs 7,5 m during 8,5 yrs Hannut F Late Paleocene Three piezometers show a similar trend than those of Vilvoorde but with a smaller increase during the nineties. Two other aquifers seem to follow the same trend.

11 This piezometer is outside the zone of the uplift. This piezometer shows a piezometric level increase of 2,85 m during 15 years. 3 The trend is positive and relatively continuous but extremely reduced compared to the other piezometers.

12 Preliminary results suggest that recharge of the groundwater aquifers and resulting groundwater level rise in the local aquifers resulted in several centimetres of elastic rebound of previously subsiding and compacting basin. => Hannut, the Cretaceous and the Cambrian aquifers record an increasing trend of the piezometric level: For the Hannut aquifer, the evolution of the piezometric level is characterized by an increase of 7,5 m during 8,5 years (june 1997 december 2005). For the Cretaceous aquifer, the evolution of the piezometric level seems to follow three steps: an increasing trend of ± 20 m before the eighties, a stable phase during the eigthies and a second increasing trend of 30 m during the nineties. An increase of 50 meters of the piezometric level during 23 years ( ) is recorded. For the Cambrian aquifer (Elis and Banque Nationake wells), the evolution of the piezometric level indicate an increase of ± 18 meters during 11 years. All the data regarding the piezometric level of these wells indicate that the increasing trends are progressive and continuous even recently (last measurements in january 2006). => Displacement time series obtained from PS cluster must be compared with piezometric groundwater measurements acquired on several wells.

13 10, , , y = 0,0039x - 142,63 y = 0,004x - 144,34 BanqueNatio Water level Linear (Water level) Linear (BanqueNatio) -5, , , mai janv oct juil avr janv oct-2006 «Banque Nationale» well - Cluster of PS (blue) inside a buffer of 250 meters around the well. - Evolution of the piezometric level (mallow). a clear relation exists

14 10, ,0000 y = 0,0054x - 196, ,0000 y = 0,0026x - 89, , lavallée Water level Linear (lavallée) Linear (Water level) -10, , , mai janv oct juil avr janv oct juil-2009 «Lavallee» well - Cluster of PS (blue) inside a buffer of 250 meters around the well. - Evolution of the piezometric level (mallow). no clear relation

15 10, , , , ,0000 0,0000-2,0000 y = -0,0003x + 9, axa Series2 Linear (axa) Linear (Series2) -4,0000 y = 0,0006x + 34, , , , mai janv oct juil avr janv oct juil-2009 «Axa» well - Cluster of PS (blue) inside a buffer of 250 meters around the well. - Evolution of the piezometric level (mallow). no relation relatively stable trends

16 Evolution of the mean piezometric level from 1883 to , ,4 Absolute level in m ,25-13, ,1-12,6 Cretaceous , , Years The evolution of the mean piezometric level of the Cretaceous aquifer is reported by Nuttinck, J.-Y. (1991). The piezometric level is at m in 1883 and decreases continuously down to 40.9 m in 1966 (a decrease of 57,15 m is thus recorded). The level increases after 1966 progressively up to 10.1 m in 1991 (30,8 m during 25 years).

17 The Alluvial plain of the Woluwe river

18 The Alluvial plain of the Woluwe river In the Woluwe valley, 6 zones of subsidence are clearly highlighted with the IDW interpolation. These zones numbered 1 to 6 from south to north are characterized by minimal average annual velocities of -5.94, -3.69, -2.45, , and mm/yr respectively. They are mostly located inside the recent alluvial sediments as attested by the vectorial limits of the alluvium of the geological map of Belgium (1/ scalemap) (Figure 2B). Only the zone n 5 seems to be outside the area related to the presence of the alluvium. It is also interesting to notice that a subsidence phenomena starts from the subsiding zones 2-3 towards the east (not represented on the Figure 2B). The presence of a subsidence phenomena in this zone outside the extension of the alluvium seems to be related to a small valley where lies the Kleine Beek brook.

19 The Alluvial plain of the Woluwe river Height industrial water catchments (three of them are outside the zone illustrated in Figure 2B) are present in the area and correspond to an annual average volume of approximately m³/year. A water catchment of the distributive firm of water in the Brussels Region produced itself a volume of m³/year. Five groundwater pumping are made at an average depth of 30 meters corresponding to the aquifer of the Bruxelles Formation. Two others are built down to an average depth of 12 meters in the alluvial aquifer.

20 The Alluvial plain of the Woluwe river

21 How to explain the subsidence?? piezometric evolution of the alluvial aquifer in the Woluwe valley cartography of the peat layers excessive loading due to road infrastructures on recent sediments (not compacted) compaction of peat layers (when dewatered) cone of depression due to water pumpings? Thank you

22 Areas processed in Belgium and planned for the next years

23 Areas processed in Belgium and planned for the next years