A New Technique To Measure Cross
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1. a m x 0 5 m PVC floating frame prototype Figure 3 right to explore the underlying sewer section and sediment bed The sonar also includes additional sensors to measure both rolling and pitching this information is necessary to later correct the movements of the floating frame generated by both the sewage flow and the operator The software Profiler 4640 is used to set all measurement parameters of the sonar The velocity of ultrasounds is corrected according to water temperature and salinity by in situ calibration A LMC J 0040 1 2 laser meter Figure 3 left attached vertically to the floating frame measures the distance he between the frame and the sewer ceiling this distance is used to determine both the water level h and the position of the sonar in the sewer section Its measurement uncertainty is 2 mm in the range 0 2 30 m The measured value resolution is 1 mm The floating frame is also equipped with a battery and a WiFi transmitter installed in an IP67 container battery and rn a WiFi transmitter n sonar floating frame Figure 3 Left top Sonar 11001 Multi Return Left down laser meter LMC J 0040 1 2 Right floating frame Bertrand Krajewski and Gibello 3 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 laptop Figure 4 Left manual positioning of the floating frame in the sewer Right scheme of the measurement principle Measurements for trace 4 Marker Green Distan2. d assainissement unitaire PhD thesis Universit Paris 6 ENPC Paris France 250 p Ashley R M Bertrand Krajewski J L Hvitved Jacobsen T Verbanck M editors 2004 Solids in Sewers London UK IWA Publishing Scientific and Technical Report n 14 May 2004 360 p ISBN 1900222914 Bertrand Krajewski J L Bardin J P Gibello C 2006 Long term monitoring of sewer sediment accumulation and flushing experiments in a man entry sewer Wat Sci Tech 54 6 7 109 117 Chopard P Paitry A 1985 Mesures d ensablement par capteurs ultrasoniques Service D partemental de Seine Saint Denis France rapport 24 p unpublished Dartus D Bachoc A 1988 Evaluation des capacit s du syst me CR2M pour des mesures en laboratoire Toulouse France IMFT CERGRENE rapport 70 p unpublished Fromont J Legendre L 2007 Automatisation du mesurage des s diments en r seau d assainissement Rapport de PIRD LGCIE INSA Lyon Villeurbanne France 81 p Laplace D 1991 Dynamique du d p t en collecteur d assainissement PhD thesis Institut National Polytechnique de Toulouse France 202 p Laplace D Dartus D Bachoc A 1988 D veloppement d un dispositif de mesure en continu de la hauteur de d p t en collecteur d assainissement Toulouse France IMFT rapport n 398 IMFT ESL 23 p Lorenzen A Willms M Dinkelacker A 1992 The Gottingen boat Wat Sci Tech 25 8 57 62 Morel A 2005
3. out in a 1 8 m high egg shape sewer reach same shape as shown in Figure 11 which corresponds to the most frequent section of the man entry sewers in Lyon were not successful Numerous parasitic echoes very likely due to too short distances between the sonar and the sewer walls and the sediment bed led to unusable data and profiles A modification of the sonar settings frequency internal data processing etc 1s tested in order to solve this difficulty Further work will include 1 an improvement of the shape of the floating frame to make it less sensitive to the movement of the flowing water in the sewer and to reduce the need of manual handling with poles a more autonomous equipment flowing downstream with the sewage flow will be investigated in the future 2 further improvement of the data processing macros more efficient algorithms automation of some tasks linkage with the Grand Lyon Sewer Department data base etc 8 A new technique to measure sediment profiles in sewers 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 3 the analysis of the most appropriate distance between cross section profiles to ensure a given uncertainty in the sediment volumes estimated by linear interpolation especially in cases where the sediment bed is not continuous and where local singularities may have an effect on the sediment bed connections confluence changes of slopes etc 4 a series of tests in a ope
4. probe to measure the filling of a sand trap in Seine Saint Denis Chopard and Paitry 1985 positive preliminary test were Bertrand Krajewski and Gibello 1 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 carried out to measure longitudinal sediment profiles in an experimental channel at the Institute of Fluid Mechanics in Toulouse France Dartus and Bachoc 1988 However despite its interest the measurement system was not easily usable in sewers due to technical constraints Laplace 1991 A fixed version to measure the evolution of local sediment levels at one point was developed in an experimental channel and later used in the trunk sewer n 13 in Marseille Laplace et al 1988 Laplace 1991 The measurement system included 1 an ultrasonic probe attached under a fixed floating boat and 11 a second ultrasonic probe measuring the water level in order to know the vertical position of the floating boat Figure 1 shows the measurement system and an example of results Voute 2 Bl oc J 2 e EIEEE Radier Jours Juin 89 Figure 1 Continuous measurements of water and sediment levels at a fixed position in a sewer from Laplace 1991 Lorenzen et al 1992 initially developed the G ttingen Boat prototype in order to measure the efficiency of the Gottingen Balls used for preventive sewer cleansing The catamaran type boat measured longitudinal sediment profiles by floating downstream
5. sediment area A with the AutoCAD macro The sediment volume V between two cross sections numbered k and k 1 is evaluated by linear interpolation A A vy e Att a xa 1 The integration of N successive cross section sediment profiles and areas along a sewer reach measured e g every 5 10 or 20 m allows calculating the total sediment volume Vot N I Viot 2 Vk 2 k 1 A simplified 3D representation is then drawn by the AutoCAD macro Figure 10 EXPERIMENTAL SITE Test measurements have been carried out in the Pierre S mard sewer in Lyon France Figure 9 This large trunk sewer has two lateral sidewalks which was very convenient for the first measurements and was known to have deposits A 250 m long reach with easy access has been chosen for sediment measurements Figure 9 Cross section of the Pierre S mard sewer 6 A new technique to measure sediment profiles in sewers 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 RESULTS On 20 December 2006 six cross section profiles have been measured every 20 m sediment areas sediment volumes between two sections and the total sediment volume 73 m are given in Table 1 The maximum sediment depth reaches 0 25 m in the 3 profile Table 1 Table 1 Six sediment profiles measured on 20 12 2006 profili 0 f 0555 0186 OS profil4 60 0533 BOB profile 120 0550 0184 o Total sediment volume m 73 23
6. 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 A new technique to measure cross section and longitudinal sediment profiles in sewers J L Bertrand Krajewski lx C Gibello LGCIE INSA Lyon 34 avenue des Arts 69621 Villeurbanne cedex France Direction de l Eau du Grand Lyon 20 rue du Lac BP 3103 69399 Lyon cedex 03 France Corresponding author email jean luc bertrand krajewski insa lyon fr ABSTRACT The measurement of sediment depth and profiles in sewers is still a difficult task Various attempts have been made since the 1990s to develop and apply automatic sediment measurement techniques but very few have been really implemented as routine techniques A new technique is presented in this paper aiming to measure both cross section and longitudinal sediment profiles in sewers at large scale in both space and time A marine sonar coupled to a laser meter installed on a floating frame have been tested in a large man entry sewer The measurements are non intrusive and do not disturb or modify the sediment bed Each cross section sediment profile is measured in 2 seconds with a good accuracy approximately cm The on line immediate display of the profiles on a laptop in the sewer is very helpful for the operator to check the data acquisition and to repeat the measurement in case any problem or failure is detected For data processing Excel and AutoCAD macros have been developed to automa
7. Dpt CONCLUSIONS AND PERSPECTIVES The sonar and the floating frame prototype measures cross section sediment profiles in 2 seconds with a good accuracy the uncertainty in sediment depth is approximately 1 cm in large man entry sewers The on line immediate display of the profiles on a laptop in the sewer is very helpful for the operator to check that data acquisition is correct and to repeat the measurement in case any problem or failure is detected Excel and AutoCAD macros have been developed to automatically correct raw data files to calculate sediment areas and volumes and to draw 2D and simplified 3D longitudinal views of the sediment profiles The tests have been made in close collaboration between the researchers and the sewer operator The whole equipment is rather simple to use and was rapidly adopted by the sewermen which is a positive point Measuring 13 profiles every 20 m over a 250 m long sewer reach requires only 15 minutes for a trained team of operators There is no need to empty the sewer to make measurements as required with other techniques using e g CCTV Morel 2005 The measurements are non intrusive and do not disturb or modify the sediment bed If the water level is not high enough i e the distance between the sonar and the sediment bed is too short to get measurements a simple temporary dam installed downstream the sewer reach allows doing measurement in an easy way However the first experiments carried
8. M trologie et mod lisation des s diments en r seau d assainissement Rapport de Master Recherche G nie Civil INSA Lyon Villeurbanne Septembre 2005 Oms C 2003 Localisation nature et dynamique de l interface eau s diment en r seau d assainissement unitaire PhD thesis ENPC Marne la Vall e France 186 p Verbanck M 1992 Field investigation on sediment occurrence and behaviour in Brussels combined sewers Wat Sci Tech 25 8 71 82 Bertrand Krajewski and Gibello 9
9. On 20 March 2007 nine sediment profiles have been measured every 5 m Table 2 The total volume is equal to 8 2 m over a distance of 40 m which is approximately one third of the volume 11 12 3 23 3 m measured on 20 12 2006 along the same 40 m long reach The nine cross section profiles drawn with AutoCAD are shown in Figure 10 The sediment profiles are not horizontal but show peaks and troughs which indicate clearly that traditional one point measurements with a graduated stick are not necessarily representative The profiles are also different between sections and an accurate estimation of the sediment volume along a given sewer reach may require a large number of cross section measurements especially if the sediment bed shows discontinuities Table 2 Nine sediment profiles measured on 20 03 2007 Distance X m Max sediment depth m Sediment volume m profili O 02237 0o05 1170 O profl9 40 TD otal sediment volume m 8 23 gt gt ot an 1 sh ae AN S gt a ft Se Oo go tx z ee ia oe as re ge Sa ge Ro lt rea e Q 2 y oe z lt 2 a a se a oe lt 2 se Figure 10 Nine cross section sediment profiles on 20 03 2007 in the Pierre S mard sewer Bertrand Krajewski and Gibello 7 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 Figure 11 Experimental egg shape sewer reach available at the Grand Lyon Sewer
10. cause of the rolling angle B the sediment depth Z is measured instead of the exact value Zp and the lateral distance Y is measured instead of the exact value Yo Figure 7 cross section view parallelism correction because of the non parallelism angle y the sewer width W is measured instead of the exact value Wo Figure 7 top view centring correction if the sonar is not on the central axis of the pipe then Y is not equal to Y Figure 7 top view cross section view Figure 7 Geometrical corrections of raw data After corrections the x y z file contains sediment bed coordinates corresponding to a cross section profile centred on and perpendicular to the central axis of the sewer and parallel to both the sewer walls and the invert The corrected x y z file is then imported into AutoCAD where a second macro Fromont and Legendre 2007 has been developed to draw and superimpose exactly the sewer cross section Bertrand Krajewski and Gibello 5 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 profile whose coordinates are imported from the sewer section data base of the Grand Lyon Sewer Department and the cross section sediment profile The difference between the sewer cross section area and the sediment profile area allows calculating the sediment area A Figure 8 sewer cross section sediment cross section sediment profile area A Figure 8 Calculation of the cross section
11. ce 1 00m Depth 1 10 m Distance Between Markers 1 98m Marker Red Distance 0 98m Depth 0 97 m Figure 5 On line display of cross section 2D sediment profiles and 3D view for several cross sections Profiler 4640 user manual MEASUREMENT METHOD The floating frame is introduced into the sewer through a manhole In the sewer it is maintained in the appropriate position i e parallel to the sewer wall and along the central axis by an operator by means of two poles Figure 4 left Initial settings for pitching and rolling corrections are made Then the positioning is repeated along the sewer at each section where a cross section sediment profile is measured During the experiments the distance between measurement sections were 5 or 20 m At each measurement section the height he is measured by the laser meter and the cross section sediment profile 1s measured by the 180 rotating sonar head Figure 4 right The complete profile 1s measured in 2 seconds Measurement results are immediately uploaded by the WiFi transmitter in a laptop brought in the sewer by a second operator The software Profiler 4640 supplied with the sonar then displays the 2D profile and also a 3D view This display Figure 5 allows the on line check of the data and the detection of any wrong measurement or of any failure the profile can be measured again immediately if necessary All data are recorded in the laptop for further data processing 4 A new techniqu
12. e to measure sediment profiles in sewers 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 DATA PROCESSING The sonar works with polar coordinates After conversion in Cartesian coordinates the software Profiler 4640 delivers an exportable text file containing the x y z coordinates of the sediment bed profile Figure 6 The X Y and Z coordinates centred on the sonar transducer correspond respectively to 1 the longitudinal position along the sewer set by the operator before measurement at each cross section 11 the horizontal distance between the central axis of the sewer where Y O horizontal position of the sonar and the lateral walls of the sewer and 111 the depth of the sediment bed Xm Yim f Zim heim Time 10535410 10535410 10535410 10535410 10535410 10535410 10535410 10535410 10535410 Figure 6 Extract of a raw data x y z file An Excel macro has been developed Fromont and Legendre 2007 in order to 1 remove possible obvious outliers a few number of echoes in some cross section profiles appear to be due to artefacts or correspond to locations which are outside the sewer e g Figure 5 left 2 do geometrical corrections of the raw data before further use pitching correction for the X coordinates because of the pitching angle a the abscissa X is measured instead of the exact value Xo Figure 7 side view rolling correction for the Z and Y coordinates be
13. ions along short distances e g use of endoscope by Oms 2003 or cameras by Ahyerre 1999 Consequently in order to be able to measure both cross section and longitudinal sediment profiles in sewers at large scale in both space and time under normal flow conditions and in a non intrusive way a better data acquisition technique was looked for A market review was carried out in 2005 and a marine sonar was identified as potentially usable for the above purpose Morel 2005 A preliminary test was carried out in July 2005 in a large man entry sewer in Lyon with a first prototype The results were positive and confirmed the interest of further tests with a modified sensor In 2006 2007 a specifically designed second prototype was tested Fromont and Legendre 2007 The paper presents the sensors and the equipment of the second prototype the specific data processing method which has been developed the experimental site two series of results and some conclusions and perspectives SENSORS AND EQUIPMENT The main sensor 1s a 165 mm x 65 mm modified 1 1 MHz Multi Return altimeter sonar model 11001 manufactured by Marine Electronics Ltd Figure 3 left Its rotating head scans a 180 sector with a range of measurable depth from 0 2 to 10 m Echoes are measured with a 0 9 angle step 1 e 200 measurements for each 180 sector The beamwidth of 1 6 corresponds to a theoretical distance resolution of 1 mm The sonar is attached horizontally under
14. n air experimental sewer reach Figure 11 with easy access and controlled conditions in order to investigate the repeatability and the reproducibility of the measurements the uncertainty in sediment profiles and consequently in sediments areas and volumes the effect of the nature of deposits on the profile comparison of sandy deposits having a clear water sediment interface to more organic and less dense deposits which may create a more fuzzy water sediment interface On longer term if the first positive results are confirmed this equipment will be used 1 for research experiments on sediment accumulation movements and flushing in sewers for which more sewers will be monitored more easily and frequently than with the traditional manual method using a graduated stick This should contribute to a better knowledge of the phenomena under various conditions and to improve models 2 for operational purposes like more frequent and better monitoring of zones with high risks of sedimentation monitoring the efficiency of sewer cleansing devices and a better management of the persons and the equipments of the sewer cleansing teams ACKNOWLEDGEMENTS Special thanks to R Perez and A Roibet Master Students at INSA Lyon in 2008 for their update of the data processing macros and for having re processed existing data series for this paper REFERENCES Ahyerre M 1999 Bilans et m canismes de migration de la pollution organique en r seau
15. tically correct the raw data files to calculate sediment areas and volumes and to draw 2D and simplified 3D views of the sediment profiles Examples of results for two experiments are given KEYWORDS Measurements monitoring sewer sediments sewer systems sonar INTRODUCTION The measurement of sediments deposited in sewers has always been a difficult task For operational purposes rough estimations are made by sewermen usually based on simple evaluation of sediment depth in manholes by means of a graduated stick For scientific research programmes measurements are also usually carried out manually with graduated sticks but with smaller space and time steps see e g Laplace 1991 Verbanck 1992 Bertrand Krajewski et al 2006 Manual measurements have many drawbacks especially 1 the necessity of several persons for each measurement campaign safety access 11 hard and time consuming measurements which cannot be made in several sites and along many kilometres of sewers 111 lack of cross section sediments profiles except in some very specific cases 1v impossibility to measure when high water levels and or flow velocities occur v possible disturbance of the sediment profile due to walking Various attempts have been made since the 1990s to develop and apply automatic sediment measurement techniques and methods but very few have been really implemented as routine techniques Inspired by previous measurements with an ultrasonic
16. with the sewage flow The sediment level was derived from measurements of the angles of two arms the first one pressed on the sediment layer the second one pressed on the sewer ceiling and from additional initial measurements in the absence of sediments Geometrical relations allowed calculating the sediment level and the position of the boat along the sewer Figure 2 shows the measurement system and an example of results Uncertainty of measurements was evaluated to be approximately 1 cm and reproducibility was excellent However as pointed by the authors the sediment height is measured in the middle of the pipe only and the lower arm is pressed more or less deeply into the sediment depending on its characteristics Ta H and Hy cml sediment pipe distance ml 0 T 6000 7000 7500 Figure 2 Left principle of the angle measurements Right top photo of the G ttingen boat right down example of longitudinal water and sediment profiles from Lorenzen et al 1992 2 A new technique to measure sediment profiles in sewers 11 International Conference on Urban Drainage Edinburgh Scotland UK 2008 More than fifteen years after the two above examples very few developments have been reported and according to our knowledge sewer sediment measurement has not progressed significantly see Ashley et al 2004 Morel 2005 despite innovative techniques applied in very specific circumstances for local investigat
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