Vlaamse Overheid Departement Mobiliteit en Openbare Werken

Transcription

1 Vlaamse Overheid Departement Mobiliteit en Openbare Werken Waterbouwkundig Laboratorium Langdurige metingen Deurganckdok: Opvolging en analyse aanslibbing Bestek 16EB/05/04

2 Colofon Ph o to c o ve r s h e e t : D e u r g a n c k d o k In te r n a t io n a l Ma r in e & D r e d g in g C o n s u l t a n ts Ad d r e s s : C o v e lie r s s tr a a t 1 5, An tw e r p, B e lg iu m : : E m a i l : i n f i md c.b e W e b s it e : w w w. i m d c. b e I/RA/11283/09.031/BOB page I

3 Document Identification Title: Project: Client Documentname Documentref: Bestek 16EB/05/04 Vlaamse Overheid - Waterbouwkundig Laboratorium K:\PROJECTS\11\ Opvolging aanslibbing dgd\10- Rap\DGD3\notas\RA09031_Predict SedMassDGD1_v30.docx I/RA/11283/09.031/BOB Revision Version Date Description Author Checked Approved /04/2009 Concept BOB JME/MSA MSA /05/2010 Concept BOB JME MSA /08/2010 Final BOB JME MSA Distribution List 7 Hard copy Joris Vanlede, Waterbouwkundig Laboratorium 3 Hard copy Frederik Roose, Maritieme Toegang I/RA/11283/09.031/BOB page II

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5 Table of Contents 1. INTRODUCTION AVAILABLE DATA METHODOLOGY MODEL IDENTIFICATION AND PARAMETER ESTIMATION MODEL VALIDATION PREDICTION OF DENSIMETRIC SILTATION CONCLUSIONS REFERENCES List of Tables TABLE 1: OVERVIEW OF DATA AVAILABILITY IN THE PERIOD... 1 TABLE 2: CORRELATION MATRIX BETWEEN DIFFERENT VARIABLES... 9 TABLE 3: SUMMARY OF PARAMETER VALUES APPLIED IN THE EMPIRICAL RELATIONSHIPS TABLE 4: DATA AVAILABILITY AND DREDGED MASS FOR THE PERIOD SEPTEMBER 2007 AUGUST TABLE 5: DATA AVAILABILITY AND DREDGED MASS FOR THE PERIOD MARCH 2006 AUGUST TABLE 6: ESTIMATED MEAN MASS GROWTH RATES AND ITS 95% PREDICTION CONFIDENCE INTERVAL TABLE 7: COMPARISON BETWEEN MEASURED AND ESTIMATED SEDIMENT MASS GROWTH RATES FOR DIFFERENT TIME PERIODS (NEGATIVE GROWTH RATES ARE EXCLUDED) List of figures FIGURE 1: CONCEPTUAL SILTATION MODEL WITH DREDGING... 6 FIGURE 2: HISTOGRAM OF MEASURED BULK DENSITIES IN DEURGANCKDOCK AT -17 M TAW... 7 FIGURE 3: BULK DENSITY PROFILES IN ZONE 3B OF DEURGANCKDOK ON 5 SEPTEMBER, 16 OCTOBER AND 16 NOVEMBER FIGURE 4: CONCEPTUAL DRAWING OF VOLUMETRIC AND DENSIMETRIC CHANGE... 8 FIGURE 5: COMPARISON BETWEEN MEASURED AND COMPUTED SEDIMENT MASS CHANGES (TDS), ASSUMING A LINEAR RELATIONSHIP (EQ. 1) BETWEEN SEDIMENT MASS AND VOLUME (PARAMETER EQUALS BULK DENSITY)... 8 FIGURE 6: COMPARISON BETWEEN MEASURED AND COMPUTED SEDIMENT MASS CHANGES (TDS), ASSUMING A LINEAR RELATIONSHIP BETWEEN SEDIMENT MASS AND AMOUNT OF DREDGED MASS FIGURE 7: COMPARISON BETWEEN MEASURED AND COMPUTED SEDIMENT MASS CHANGES (TDS), ASSUMING THE NON-LINEAR RELATIONSHIP OF EQ FIGURE 8: COMPARISON BETWEEN MEASURED AND COMPUTED SEDIMENT MASS CHANGES (TDS), ASSUMING THE NON-LINEAR RELATIONSHIP OF EQ FIGURE 9: ESTIMATED SEDIMENT MASS ACCUMULATION WITH ITS 95% PREDICTION CONFIDENCE INTERVAL FOR THE INVESTIGATED MODELS: EQ 2. (LEFT) AND EQ. 3 (RIGHT) I/RA/11283/09.031/BOB page III

6 FIGURE 10: ESTIMATED SEDIMENT MASS ACCUMULATION WITH ITS 95% PREDICTION CONFIDENCE INTERVAL FOR THE INVESTIGATED MODELS, EQ 2. (LEFT) AND EQ. 3 (RIGHT), WITH A DENSITY CORRECTION FOR THE USE OF THE DENSITUNE FIGURE 11: ESTIMATED SEDIMENT MASS ACCUMULATION WITH ITS 95% PREDICTION CONFIDENCE INTERVAL FIGURE 13: DREDGED MASS (TDS) PER WEEK, CUMULATIVE NATURAL INFLOW OF SEDIMENTS AND RESIDUAL SEDIMENTS IN THE DOCK. SEDIMENT MASS PRESENT IN THE DOCK AT APRIL 1 ST 2006 IS SET TO ZERO (IMDC, 2008) FIGURE 12: ESTIMATED RESIDUAL SEDIMENT MASS IN DEURGANCKDOK I/RA/11283/09.031/BOB page IIII

7 1. INTRODUCTION Th is me mo is p a r t o f th e s tu d y L o n g -te r m me a s u r e me n ts in D e u r g a n c k d o k : m o n i to r i n g a n d a n a l ys is o f s i l t a t i o n. Th e te r ms o f r e fe r e n c e fo r th is s tu d y w e r e p r e p a r e d b y th e D e p a r te me n t Mo b i li te i t e n Op e n b a r e W e r k e n va n d e Vla a ms e O v e r h e id, Af d e l i n g W a te r b o u w k u n d ig L a b o r a to r iu m ( 1 6 E B/ 0 5 /0 4 ). In a p e r i o d o f th r e e ye a r s, i. e. Ap r i l Ap r i l , s il ta tio n o f D e u r g a n c k d o k w a s mo n i to r e d. Th e s tu d y a ime d a t s e t t i n g u p a s e d im e n t ma s s b a l a n c e. Th e r e fo r e, b u lk d e n s i t y me a s u r e me n ts w e r e p e r f o r me d o n a r e g u la r b a s is. In p a r a lle l, d e p th s o u n d in g d a ta w e r e c o lle c te d a s w e ll. T h e d e n s it y me a s u r e me n ts w e r e e xe c u te d fr o m Se p te mb e r o n, r e s u l tin g in o n e ye a r a n d a h a l f w i th o u t a n y s e tt le d s e d i me n t ma s s d a ta. Fr o m Ap r il t il l Se p te mb e r , o n ly d e p th s o u n d in g d a ta w a s c o l le c te d. Th is me mo th e r e fo r e tr ie s t o s e t u p a r e l a t io n b e tw e e n th e te mp o r a l c h a n g e o f s e d ime n t m a s s a n d b e d h e ig h t in o r d e r to e n a b le a n e s t ima ti o n o f th e s e t tl e d s e d ime n t ma s s in p e r io d s w ith o u t a n y b u lk d e n s i t y me a s u r e me n t s. Th e me m o c o n s is ts o f t h e f o llo w in g c h a p t e r s : o ve r v ie w o f d a ta a va il a b i li t y in o r d e r t o s e t u p a n e mp ir ic a l r e l a t io n s h i p b e t w e e n me a s u r e d vo lu me tr ic a n d d e n s ime tr ic b e d c h a n g e s ( C h a p te r 2); a p p l ie d me th o d o lo g y ( C h a p t e r 3) s e t-u p o f th is e mp ir ic a l m o d e l ( C h a p te r 0); mo d e l va li d a t i o n ( C h a p t e r 5 ) ; a p p l ic a t io n o f th e e mp ir ic a l mo d e l ( C h a p t e r 6 ) ; a n d c o n c lu s io n s ( C h a p te r 7) 2. A V A I L A B L E D A T A D a ta is a v a i la b le w i th r e s p e c t to d r e d g in g a mo u n ts, b u lk d e n s i t y a n d s e d i me n t b e d h e ig h t fo r th e p e r io d Ap r i l u n t il A p r i l D a ta u s e w a s n o t r e s tr ic t e d to o n l y t h e s e c o n d me a s u r e me n t ye a r ( w ith r e s p e c t to d e n s i t y me a s u r e me n ts ) i n o r d e r to h a v e a l a r g e r d a t a s e t. A c h r o n o lo g ic a l o ve r v ie w is g iv e n i n Table 1. Th e t a b l e c le a r l y in d ic a te s th a t d e n s i t y me a s u r e me n ts w e r e o n l y a va ila b le fr o m Se p t e mb e r o n. R e ma r k t h a t d e n s i t y me a s u r e me n ts w e r e p e r fo r me d w ith t h e N a vi tr a c k e r d e v ic e t il l Au g u s t , a f te r w h ic h th e D e n s itu n e w a s u s e d. T h is h a s a n i n f lu e n c e o n th e d e n s i t y me a s u r e me n ts, c f. I MD C ( ). Table 1: O v e r v i e w o f d a t a a v a i l a b i l i t y in the period d ep th so u n d i n g 24/03/ /04/ /04/ /04/ /05/2006 d e n s i t y p r o f i l e s d r ed g i n g s t a r t end 20/02/ /02/ /02/ /02/2006 6/03/ /03/ /03/ /03/ /03/ /03/ /04/2006 6/05/ /05/ /05/2006 I/RA/11283/09.031/BOB page 1

8 d ep th so u n d i n g d e n s i t y p r o f i l e s d r ed g i n g 26/05/ /05/ /05/2006 s t a r t end 29/05/2006 4/06/2006 9/06/2006 6/06/ /06/ /06/2006 7/07/2006 3/07/2006 8/07/ /07/2006 4/08/2006 7/08/ /08/ /08/2006 1/09/ /08/2006 3/09/ /09/ /10/2006 8/12/ /02/ /03/ /04/ /05/ /06/ /07/ /08/ /09/ /09/ /10/ /10/ /11/ /11/ /12/ /12/ /01/ /01/2008 2/10/2006 8/10/2006 9/10/ /10/ /10/ /10/ /02/ /02/ /03/ /03/2007 2/04/2007 7/04/2007 9/04/ /04/ /08/ /08/ /08/ /08/ /11/ /11/ /11/ /11/ /01/ /02/ /02/ /02/2008 I/RA/11283/09.031/BOB page 2

9 d ep th so u n d i n g d e n s i t y p r o f i l e s 15/02/ /02/ /03/ /04/2008 9/05/ /4/ /06/ /06/ /08/ /08/ /08/ /08/2008 3/09/ /09/ /09/2008 6/10/ /10/ /10/2008 7/11/2008 6/11/ /11/ /01/2009 s t a r t d r ed g i n g end 11/02/ /02/ /02/ /02/ /03/ /03/ /05/ /05/ /05/ /05/ /05/ /06/ /08/ /08/ /08/ /08/ /10/ /10/ /02/ /01/2009 9/02/ /02/2009 3/03/ /03/ /03/ /02/ /02/ /02/2009 1/03/ /04/ /04/ MET H O D O L O G Y In o r d e r t o c a lc u la te th e s e d ime n t ma s s g r o w th b a s e d o n a tim e s e r ie s o f d e p th s o u n d in g d a t a o f D e u r g a n c k d o k, a n e mp ir ic a l r e la ti o n b e tw e e n th e s e tw o va r ia b le s is t o b e s e t u p. E xp e r ie n c e g a i n e d d u r in g th e s e d ime n t b a la n c e a n a l y s is r e p o r ts is a p p l ie d. It w a s in d e e d o b s e r ve d th a t in c r e a s e d s il ta t io n r a te s, b o th vo lu me tr ic a n d d e n s ime tr ic, o c c u r a ft e r d r e d g in g a c t iv i ti e s. Th e s e s il t a t io n r a te s lo w e r ti ll a s te a d y va l u e ( a s lo n g a s th e h y d r o d y n a m ic c o n d i ti o n s in s id e th e d o c k d o n o t c h a n g e t o o d r a s t ic a l ly). F r o m Table 1, it is cle a r th a t n o s ys te ma ti c d e p t h s o u n d in g s h a v e b e e n p e r fo r me d imme d ia te l y b e fo r e a n d a f te r d r e d g in g d u r in g th e f ir s t ye a r o f me a s u r e me n ts. Th is c o mp l ic a te s th e c a lc u l a t io n s b e c a u s e, fr o m ti me to ti me, o n l y o n e d e p th s o u n d in g me a s u r e me n t is p e r f o r me d b e tw e e n t w o s u b s e q u e n t d r e d g in g o p e r a tio n s. In o r d e r to c a lc u la te th e s e d ime n t ma s s g r o w th i n th e d if fe r e n t d o c k z o n e s, a c o n c e p tu a l mo d e l fo r th e I/RA/11283/09.031/BOB page 3

10 s itu a t io n o f s u b s e q u e n t d e p th s o u n d i n g s w it h in te r mi t t e n t d r e d g in g i s p r o p o s e d in Fig u r e 1. A n imp o r ta n t a s s u mp t io n h e r e is ma d e w ith r e s p e c t t o t h e d r e d g in g i mp a c t o n t h e d e n s i ty p r o f ile a n d is b a s e d o n t h e ( i) me a s u r e d d e n s it y p r o f ile s, a n d ( ii) d r e d g i n g o p e r a tio n me t h o d : d r e d g in g o p e r a t io n me th o d : Til l Au g u s t 3 1 s t , th e h o p p e r h e a d s u c k e d a w a y t h e s e d i me n t mi xt u r e a t -17 m TAW. In a s e c o n d r u n, t h e r e ma in in g s e d ime n t w a s d r e d g e d a t th e s a me d e p th. I t w a s h o w e ve r e xp e r ie n c e d th a t th e n o n -d r e d g e d to p b e d la ye r d i d n o t s e t t le th a t q u ic k l y s o th e s e c o n d r u n w a s u n a b l e to remove the top layer. See phase 3 in F ig u r e 1. b u lk d e n s i t y p r o f ile s : Al th o u g h th e b u lk d e n s i t y p r o f ile s a r e i n f l u e n c e d b y s u b s e q u e n t d r e d g in g o p e r a t i o n s, i t is a s s u me d th a t a s mo o t h p r o f ile e xis t s a s s h o w n in p h a s e 1 o f Fi g u r e 1. W i t h r e s p e c t t o t ime p e r io d s w i th o u t d r e d g in g, o n e is r e fe r r e d to 0 a n d F ig u r e 4. H o w e ve r, a f te r d r e d g i n g, t h e to p b e d la y e r s e t tl e s a g a in a n d is s lig h t ly s tir r e d u p b y d e w a t e r in g p r o c e s s e s lik e c h a n n e lin g. I t is h e r e a s s u me d th a t th is d o e s n o t a f fe c t th e lo c a l b u lk d e n s i ty, i.e. th e to p l a ye r is s i mp l y v e r t ic a l ly tr a n s l a te d r e s u l t i n g in th e b u lk d e n s i t y p r o fi le o f p h a s e 4 in F ig u r e 1. T h e r e s u lt in g d e n s i t y a t -1 7 m T A W d o e s n o t s h o w la r g e ve r tic a l g r a d ie n ts s o t h a t th e p r o f ile b e fo r e d r e d g i n g is n o t a l te r e d a lo t. With the assumptions mentioned above, the mass growth can be estimated in two possible ways: calculate mass growth with an empirical relation, and add the dredged mass to the calculated mass growth; calculate the mass growth with an empirical relation, but with volumetric changes corrected for the dredged mass. In the latter case, a representative bulk density at -17 m TAW should be determined from the density measurements for, e.g., the period September 2007 August Based on 356 density profiles, an average density of ± TDS/m³ could be determined at a depth of -17 m TAW (Figure 2). However, this method of corrected volumetric changes returned a too large sediment accumulation in the dock in comparison to the former method (~24%) and the results of IMDC (2008). Therefore, the former method is selected. Because predictions of sediment mass growth are made based on statistically determined relations, uncertainty on the predictions should be considered. For this reason, prediction confidence intervals for the mass growth (see Seber and Wild (1989) for the methodology) are determined. Note however that other uncertainties are unquantified and are related to: conceptual model assumptions; uncertainty on dredged mass amount; using the model outside its calibration range; Fr o m th e m e a s u r e me n ts, i t is p o s s ib le t o c o mp u te th e to ta l s e d im e n t ma s s fr o m d e n s i t y p r o fi le s a n d t h e s e d ime n t vo l u me fr o m th e d e p th s o u n d in g s ( i.e k H z a c o u s tic r e fl e c ta n c e s ig n a l) fo r t h e d if fe r e n t d e f in e d z o n e s in D e u r g a n c k d o k. C o mp u te d c o r r e la t io n s b e tw e e n th e s e tw o va r ia b l e s a r e l a r g e. Te mp o r a l c h a n g e s o f t h e s e va r ia b le s a r e s ma l l i n c o mp a r is o n t o th e to ta l va l u e s a n d, t h e r e fo r e, e xp la in s th e la r g e c o r r e la tio n s ( ~ fo r z o n e s 3 A-C ). It h a s in d e e d b e e n o b s e r ve d t h a t c o r r e la tio n s b e tw e e n t h e te m p o r a l c h a n g e o f s e d ime n t ma s s a n d vo lu me a r e mu c h lo w e r ( ~ fo r z o n e s 3 A -C ). Pr e d ic t io n s o f te mp o r a l in c r e me n ts o f b e d h e ig h ts a n d a c c u mu l a te d s e d ime n t ma s s a r e n e ve r th e le s s p r e fe r r e d b e c a u s e it is th is va r ia b i l it y o n e is i n t e r e s te d i n. In o r d e r t o d e te r m in e the relationship with a minimum of external influences, i t is c r u c ia l to c o n s i d e r ma s s a n d vo lu m e in c r e a s e s in p e r io d s u n d is t u r b e d b y d r e d g i n g a c t iv i tie s. Fu r th e r, i t is v e r y i mp o r ta n t to va l id a te th e c a lib r a te d mo d e l a n d i n ve s ti g a te w h e th e r th e m o d e l r e tu r n s g o o d p r e d ic t io n s o u ts i d e i ts va l id a t ion r a n g e. Fo r t h a t r e a s o n, i t is d e c id e d to s p l it th e d a t a s e t in tw o fo r m o d e l c a l ib r a ti o n a n d va li d a tio n : c a lib r a t io n p e r io d : 0 9 / / va lid a t io n p e r i o d : 0 9 / / Fr o m Table 1, o n l y fo u r c a li b r a t io n p e r io d s a r e d e te r mi n e d b e in g u n d is t u r b e d b y d r e d g in g. I/RA/11283/09.031/BOB page 4

11 Th e mo d e l p a r a me te r e s t im a t io n is p e r fo r me d b y mi n im iz in g th e s u m o f s q u a r e d e r r o r s b e tw e e n o b s e r ve d a n d c a lc u la te d va lu e s. Fo r th e p r e d ic ti o n o f s e d ime n t a c c u mu la ti o n, t h e 9 5 % p r e d i c tio n c o n fid e n c e in te r va l is d e t e r mi n e d b a s e d o n t h e me t h o d o lo g y o f S e b e r a n d W ild ( ). I/RA/11283/09.031/BOB page 5

12 F i g u r e 1: Conceptual siltation model w ith dredging I/RA/11283/09.031/BOB page 6

13 F i g u r e 2: Histogram of measured bulk densities in Deurganckdock at -17 m TAW 4. M O D E L I D E N T I F I C A T I O N A N D P A R A M E T E R E S T I M A T I O N In th e d i f fe r e n t d o c k z o n e s, s e d ime n t s e t tl e s a n d c o n s o lid a t e s r e s u l tin g n o t o n l y in a c h a n g e o f th e b e d h e ig h t b u t a ls o in th e b u lk d e n s i ty p r o fi le. W ith o u t a n y e x te r n a l d is tu r b a n c e s lik e d r e d g in g, it is h y p o th e s iz e d th a t th e b e d h e ig h t in c r e a s e s a n d th e d e n s it y p r o fi le is ve r tic a ll y tr a n s la t e d to a c e r ta in e x te n t. A n e xa mp le is s h o w n in Fig u r e 3. A f t e r a d r e d g in g o p e r a t io n, a r a p id s e d i me n t a c c u mu la tio n in t h e d o c k o c c u r s b e c a u s e th e s e d ime n t b e d i s s itu a te d l o w e r th a n th e s i l l le ve l ( a p p r m T AW ) ; h e n c e, t h e d o c k c a n b e con s id e r e d a s a s e d ime n t tr a p Sept Oct Nov depth (m) bulk density (kg SSC/L) F i g u r e 3: Bulk density profiles in zone 3B of Deurganckdok on 5 September, 16 October and 16 November 2007 W h e n o n l y fo c u s in g o n th e te m p o r a l c h a n g e in s e d im e n t ma s s a n d vo lu me, o n e c a n w r it e t h e fo llo w in g s i m p l e f i r s t -a p p r o a c h r e la t io n ( s e e F ig u r e 4): (E q 1) w i t h : I/RA/11283/09.031/BOB page 7

14 Bulk density Volumetric change depth mass change F i g u r e 4: conceptual drawing of volumetric and densimetric change Th is s imp le r e la tio n le a d s to a c o r r e la tio n o f ; a l o t o f va r ia t io n is s ti ll u n e xp l a in e d b y th e mo d e l a s s h o w n in Fig u r e 5. Th e a ve r a g e s e d i m e n t c o n c e n tr a t io n is h e r e c a lc u la te d a s TD S /m³. T h i s c o r r e s p o n d s t o a b u lk d e n s it y o f to n n e s / m ³, w h ic h is in th e r a n g e o f c o n c e n tr a t io n s a t th e t o p o f th e s e d ime n t b e d, c f. F ig u r e 3. F i g u r e 5: Comparison between measured and computed sediment mass changes ( T D S ), assuming a linear relationship ( E q. 1 ) between sediment mass and volume (parameter equals bulk density) Th e c h a n g e i n s il ta t io n r a t e a lo n g th e d o c k s le n g t h i s in tr in s ic a l l y c o n s id e r e d in th e te mp o r a l a n d s p a t ia l c h a n g e o f vo l u me a n d s e d i me n t ma s s. H o w e ve r, s e v e r a l p h ys ic a l p h e n o me n a a r e n o t c o n s id e r e d in th is s imp l e r e la t io n s h ip, s u c h a s in c r e a s e d s il ta ti o n r a te s a f t e r d r e d g in g. Mo r e s p e c i fic a ll y, i t w a s o b s e r ve d th a t : th e d e n s ime tr i c ma s s g r o w t h r a te in c r e a s e d w it h th e to t a l d r e d g e d a mo u n t ; I/RA/11283/09.031/BOB page 8

15 th e d e n s im e tr i c ma s s g r o w t h r a te d e c r e a s e d w it h t h e ti me p e r i o d b e t w e e n d r e d g in g o p e r a ti o n a n d de p t h s o u n d i n g. In o r d e r to in v e s ti g a te t h e i mp o r ta n c e o f d i ff e r e n t v a r ia b le s, th e c o r r e la tio n ma tr i x i s c a lc u la te d b e tw e e n : th e m a s s c h a n g e b e tw e e n t w o s u b s e q u e n t d e n s i ty me a s u r e me n ts ( M ) th e ( s e d ime n t ) vo l u me tr ic c h a n g e b e tw e e n tw o s u b s e q u e n t d e p th s o u n d in g s ( V ) ; th e m a s s d r e d g e d b e tw e e n tw o s u b s e q u e n t d e n s i t y m e a s u r e me n ts ( M d ); th e ti me p e r io d b e tw e e n tw o s u b s e q u e n t d e p t h s o u n d i n g s ( T d s -d s ) ; a n d th e ti me b e tw e e n th e d e p th s o u n d in g a n d th e l a s t o c c u r r in g d r e d g in g mo me n t ( T d-d s ). R e ma r k h o w e ve r th a t t h e c o r r e la ti o n m a t r ix a s s u me s a li n e a r r e la t io n s h ip b e tw e e n t h e d i ff e r e n t va r ia b le s. Th is is n o t n e c e s s a r il y th e c a s e, b u t th e c o r r e la t io n a llo w s th e id e n t i fic a ti o n o f imp o r ta n t r e l a t io n s h i p s b e tw e e n t h e ma s s c h a n g e a n d o t h e r v a r ia b le s. Th e r e s u lts a r e s h o w n i n Ta b l e 2, fr o m w h i c h c a n b e c o n c lu d e d th a t : a la r g e c o r r e l a t io n o f e x is ts b e tw e e n M a n d M d : th is c o n f i r ms th e o b s e r va ti o n o f fa s te r siltation in function of th e a mo u n t o f d r e d g e d ma s s ; a la r g e c o r r e l a t io n o f e xis ts b e tw e e n M a n d V ( a s e xp e c te d ) ; M is n e g a t i v e l y c o r r e la te d w i th T d-d s, i. e. th e l o n g e r th e d e p th s o u n d in g is s e p a r a te d fr o m th e d r e d g in g mo me n t, th e lo w e r th e m a s s a c c u mu la ti o n is. T d s -d s a n d T d-d s s h o w a la r g e p o s i ti v e c o r r e la ti o n s o o n e o f t h e m c a n b e c o n s id e r e d a s r e d u n d a n t. Table 2: C o r r e l a t i o n m a t r i x b e t w e e n d i f f e r e n t v a r i a b l e s M V M d T d s -d s T d-d s M V M d T d s -d s T d-d s Fr o m th e s e r e s u l ts, i t s e e ms o b v io u s t o r e ta in a l in e a r r e la t io n s h ip b e tw e e n M a n d M d. A c o mp a r is o n b e tw e e n c a lc u la te d a n d o b s e r ve d ma s s c h a n g e s is s h o w n in F i g u r e 6. C le a r ly, th e r e s u l t s c a n b e imp r o ve d. Af t e r te s tin g s e v e r a l mo d e l s tr u c tu r e s, i t a p p e a r e d t h a t a n e xp o n e n tia l r e la tio n b e tw e e n M a n d M d, in c o mb i n a t io n w i th V, g a ve g o o d r e s u lts w i th a c o r r e la ti o n o f N o te th a t th e e xp o n e n t ia l r e l a t io n a lo n e g a ve a c o r r e la t io n o f ; th e c a u s e o f th e i mp r o ve d c o r r e la tio n c a n b e a ttr ib u te d t o t h e la r g e c o r r e la tio n b e tw e e n M d a n d V. Th e ir a p p e a r a n c e together in Eq. 2 results in an improved model p e r fo r ma n c e, s e e F ig u r e 7. w i t h : ( E q. 2 ) I/RA/11283/09.031/BOB page 9

16 F i g u r e 6: Comparison between measured and computed sediment mass changes ( T D S ), assuming a linear relationship between sediment mass and amount of dredged mass F i g u r e 7: Comparison between measured and computed sediment mass changes ( T D S ), assuming the non-linear r e l a t i o n s h i p of Eq. 2 I/RA/11283/09.031/BOB page 10

17 Fu r th e r e xt e n d in g Eq. 2 w i t h a c o r r e c ti o n te r m fo r T d-d s results in a correlation coefficient of 0.97: w i t h : ( E q. 3 ) R e s u lts o f th e mo d e l p e r fo r ma n c e a r e s h o w n in Fi g u r e 8. Physically, th e la t te r c o r r e c tio n c a n b e in te r p r e te d a s fo llo w s : w h e n d r e d g in g ta k e s p la c e, th e u p p e r s e d ime n t la ye r s a r e r e mo ve d. As lo n g a s t h e s e d im e n t b e d is s i tu a te d d e e p e r th a n t h e s il l le ve l, s e d ime n t is tr a p p e d in th e d o c k a n d a c c u mu la te s q u i c k ly. W h e n th e s e d i me n t b e d a p p r o a c h e s th e s i ll le ve l, s e d ime n t a c c u mu la t io n s lo w s d o w n. As a r e s u l t, th e c a lc u la te d s e d ime n t ma s s c h a n g e in c r e a s e s w ith th e a mo u n t o f d r e d g e d s e d i me n ts a n d t h e ti me b e tw e e n d r e d g in g a n d th e d e p t h s o u n d in g. Th e mo d e l p a r a me te r s fo r E q. 2 a n d 3 a r e s u mm a r iz e d i n Table 3. F i g u r e 8: Comparison between measured and computed sediment mass changes ( T D S ), assuming the non-linear r e l a t i o n s h i p of Eq. 3 Table 3: Summary of parameter values applied in the empirical relationships Parameters E q. 2 E q I/RA/11283/09.031/BOB page 11

18 5. M O D E L V A L I D A T I O N Th e a im o f th is c h a p te r is t o va li d a te th e s ta tis tic a l s e d ime n ta t io n mo d e l w i th a n in d e p e n d e n t d a ta s e t o f d e p t h s o u n d i n g, d r e d g in g a mo u n ts a n d d e n s ime tr ic me a s u r e me n ts. Th e va li d a t io n d a ta c o n s is ts o f d e n s ime tr ic m e a s u r e me n ts p e r fo r me d i n th e p e r io d Se p te mb e r Ma r c h C o mp a r is o n p lo ts o f o b s e r ve d vs. me a s u r e d va l u e s c a n n o t b e p r e p a r e d b e c a u s e t ime s o f p r e d ic tio n s a n d o b s e r v a t io n s d o n o t c o r r e s p o n d. F o r t h a t r e a s o n, tr e n d p lo ts o f b o t h c o m p u t e d a n d me a s u r e d s e d ime n t ma s s a c c u m u la tio n a r e ma d e. R e s u l t s a r e s h o w n i n Fi g u r e 9 fo r b o th i n v e s t ig a te d mo d e ls ( c f. Eq. 2 a n d E q. 3 ), a n d c le a r l y in d ic a te t h a t both E q. 2 a n d 3 u n d e r p r e d ic t t h e s e d ime n t m a s s a c c u mu la t io n. Th e c a u s e o f th is u n d e r e s ti ma t io n is r e la t e d to th e u s e o f a d i ff e r e n t d e n s i t y me a s u r e me n t te c h n iq u e th a n th e o n e a p p li e d d u r in g t h e c a lib r a t io n p e r i o d, i.e. t h e D e n s itu n e is a p p lie d in th e va lid a t io n p e r io d in s te a d o f th e N a vi tr a c k e r. IMD C ( ) r e ma r k s t h a t th e D e n s i Tu n e s ys te m a t ic a l ly o ve r e s tim a t e s lo c a l d e n s it ie s w h ic h ma y e x p la i n t h e d if fe r e n c e s b e tw e e n c o mp u ta ti o n s a n d o b s e r va ti o n s in Fi g u r e 9. W h e n a c c o u n t in g fo r a n a v e r a g e o ve r e s ti ma t io n o f T D S/ m² ( s e e I MD C, ) f o r z o n e s 3 A -D, 4NA-C a n d 4 ZA-C, a c o r r e c ti o n o n th e c o mp u te d a c c u mu l a t e d s e d ime n t ma s s c a n b e ma d e. Th e r e s u l ts a r e s h o w n i n Fig u r e 1 0 fo r b o th Eq. 2 a n d Eq.3. C l e a r l y, Eq. 3 p e r fo r ms b e s t a n d w i ll b e r e t a in e d f o r th e p r e d ic tio n o f a c c u mu la te d s e d ime n t m a s s in th e p e r io d Ma r c h 2006 Au g u s t ( s e e 6). F i g u r e 9: Estimated sediment mass accumulation with its 95% prediction confidence interval for the invest i g a t e d m o d e l s : E q 2. ( l ef t ) a n d E q. 3 ( r i g ht ) F i g u r e 10: Estimated sediment mass accumulation with its 95% prediction confidence interval for the investigated models, Eq 2. (left) and Eq. 3 (right), with a density correction for the use of the DensiTune I/RA/11283/09.031/BOB page 12

19 6. P R E D I C T I O N O F D E N S I M E T R I C S I L T A T I O N Th e g o a l o f t h e s ta tis t ic a l mo d e l is t o p r e d ic t th e s e d i me n t ma s s g r o w th in D e u r g a n c k d o k in th e p e r io d o f 2 4 /0 3 / /0 8 / Th is p e r i o d in c lu d e s th e me a s u r e m e n t c a m p a ig n s o f th e m e a s u r e me n t c a mp a ig n s D GD 1 a n d th e fir s t h a lf o f D GD 2. Th e la t t e r in in c lu d e d b e c a u s e a ls o fo r t h is p e r i o d n o d e n s it y me a s u r e me n t s w e r e a va i la b le. An o ve r v i e w o f a va i la b l e d a ta w i th r e s p e c t t o d r e d g in g a n d d e p t h s o u n d in g s i s g i v e n i n Table 5. Results of the predicted sediment mass growth rate are shown in: Table 6: predicted mean sediment mass growth rates with their 95% prediction confidence intervals; Figure 11: predicted total sediment mass accumulation in zones 4A-C, 4NA-NC and 4ZA-4ZC with its 95% prediction confidence interval; also the dredging times are indicated. Clearly, increased siltation of the dock is computed after dredging, in correspondence with previous observations (eg. IMDC (2007)) A model validation has already been performed in 5. Further, an evaluation of the prediction quality can also be made with: measured mass growth rates in the periods of August October 2005 and September 2007 September 2008 (see Table 7): Table 7 clearly indicates that measured sediment mass growth rates generally situate in the 95% confidence interval of the predicted growth rates. Note that the confidence intervals are large, which is proportional to the original data heterogeneity. Sweepbeam dredging is e.g. not included in the model as indicated in Eq. 2 and, thus, its exclusion from the model will lead to possible inaccurate calculations. Obviously, using Eq. 2 outside its calibration range may result in errors too (even though the model validation returns good results). the computed evolution of sediment accumulation in the dock based on a physically-based data-driven model (IMDC, 2008), see Figure 12. Because the latter model computes the sediment fluxes at the dock entrance ( in and out ), it returns order of magnitudes of sediment accumulation in the dock, which can be used to validate qualitatively the results of Figure 11. The following observations can be made: o First, the residual accumulated sediment mass (after a one-year period with dredging) in the dock can be compared. Whereas IMDC (2008) returns a sediment mass of around 10 5 TDS in April 2007 (see Figure 12), this study gives an accumulation of TDS (see Figure 13). The order of magnitude is similar though when the confidence intervals on the calculated sediment mass accumulation are accounted for (in this study and IMDC(2008)). o Second, the natural siltation can be compared as well. Generally speaking, it can be concluded that the order of magnitudes are comparable, taking into account the confidence bands determined in this study and IMDC (2008). Note that the impact of dredging activities is more pronounced in this model in comparison with IMDC (2008). It is indeed implicitly considered in the current model whereas IMDC (2008) does not. I/RA/11283/09.031/BOB page 13

20 F i g u r e 11: Estimated sediment mass accumulation with i t s 9 5 % prediction confidence interval 2006 F i g u r e 12: Dredged mass (TDS) per week, cumulative natural inflow of sediments and residual sediments in the dock. Sediment mass present in the dock at April 1 s t i s s e t t o z e r o (IMDC, 2008) 2007 I/RA/11283/09.031/BOB page 14

21 7. CONCLUSIONS F i g u r e 13: Estimated residual sediment mass in Deurganckdok Th is me mo tr i e d to s e t u p a n e mp ir ic a l mo d e l to c o m p u te th e s e d i me n t ma s s a c c u mu la ti o n i n th e d o c k b a s e d o n a t i me -s e r ie s o f d e p t h s o u n d in g s. Th e r e s u l t i n g n o n -lin e a r mo d e l in c lu d e s e f fe c ts o f d r e d g in g a n d th e s iz e o f t h e ti me in te r va l b e tw e e n d e p t h s o u n d i n g a n d p r e c e d in g d r e d g i n g a c ti v i tie s. C o n fid e n c e in te r va ls o n p r e d ic te d d e n s i me tr ic c h a n g e s a r e d e te r mi n e d a s w e ll. A v a l id a ti o n s tu d y r e ve a le d g o o d p r e d i c tio n c a p a b il i t ie s w i th a n i n d e p e n d e n t d a ta s e t. W i t h r e s p e c t to p r e d ic tin g s e d ime n t ma s s a c c u mu la ti o n i n th e fir s t ye a r o f c o n d u c te d me a s u r e me n ts, i t c o u ld b e c o n c lu d e d th a t th e s a m e o r d e r s o f ma g n i tu d e a r e o b ta i n e d fo r me a s u r e d g r o w th r a te s a n d r e s u lts o f p r e v io u s e mp ir ic a l m o d e ls d e s c r ib in g th e i n c o mi n g a n d o u tg o i n g s e d ime n t fl u x a t th e d o c k e n tr a n c e ( I MD C, ). 8. R E F E R E N C E S IMDC (2007). Langdurige metingen Deurganckdok: opvolging en analyse aanslibbing. Deelrapport 1.12: Sediment balans 01/09/ /12/2007 (I/RA/11283/07.083/MSA) IMDC (2008). Langdurige metingen Deurganckdok: opvolging en analyse aanslibbing. Deelrapport 4.1: Analyse van aanslibbingsprocessen en invloeden (I/RA/11283/06.129/MSA) IMDC (2010). Langdurige metingen Deurganckdok: opvolging en analyse aanslibbing. Deelrapport 1.24: Sediment jaarbalans 01/04/ /03/2009 (I/RA/11283/08.080/MSA) Seber G.A.F. and Wild C.J. (1989) Nonlinear regression. John Whiley and Sons, New York. I/RA/11283/09.031/BOB page 15

22 Table 4: D a t a availability and dredged mass f o r the period September 2007 August 2008 dredged mass (TDS) peiling prikken bagger 3a 3b 3c 3d 4NA 4NB 4NC 4ZA 4ZB 4ZC 20/08/ /08/ /08/ /08/ /09/ /09/ /10/ /10/ /11/ /11/ /11/ /11/ /11/ /11/ /12/ /12/ /01/ /01/ /01/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /03/ /03/ /03/ /04/2008 9/05/ /05/ /05/ /05/ /06/ /06/ /06/ /08/ /08/2008 I/RA/11283/09.031/BOB page 16

23 dredged mass (TDS) peiling prikken bagger 3a 3b 3c 3d 4NA 4NB 4NC 4ZA 4ZB 4ZC 11/08/ /08/ /08/ /08/ /08/ /08/ Table 5: D a t a availability and dredged mass for the period March 2006 August 2007 dredged mass (TDS) peiling bagger 3a 3b 3c 3d 4NA 4NB 4NC 4ZA 4ZB 4ZC 06/03/ /03/ /03/ /03/ /03/ /03/ /03/ /04/ /04/ /04/ /04/ /05/ /05/ /05/ /05/ /05/ /05/ /05/ /05/ /06/ /06/ /06/ /06/ /06/2006 I/RA/11283/09.031/BOB page 17

24 dredged mass (TDS) peiling bagger 3a 3b 3c 3d 4NA 4NB 4NC 4ZA 4ZB 4ZC 07/07/ /07/ /08/ /08/ /09/ /09/ /10/ /12/ /02/ /03/ /04/ /05/ /06/ /07/ /07/ /07/ /08/ /08/ /08/ /09/ /10/ /10/ /10/ /10/ /10/ /10/ /02/ /02/ /03/ /03/ /04/ /04/ /04/ /04/ I/RA/11283/09.031/BOB page 18

25 dredged mass (TDS) peiling bagger 3a 3b 3c 3d 4NA 4NB 4NC 4ZA 4ZB 4ZC 20/08/ /08/ /08/ /08/ /08/2007 I/RA/11283/09.031/BOB page 19

26 Table 6: Estima ted mean mass growth rates and its 95% prediction confidence interval **Estimated mean mass growth (kg/m²/day) sounding1 sounding2 3A 3B 3C 4NA 4NB 4NC 4ZA 4ZB 4ZC 24/03/ /04/ /04/ /04/ /04/ /04/ /06/ /06/ /09/ /09/ NaN NaN NaN 23/10/ /12/ /12/ /02/ /04/ /05/ /05/ /06/ /06/ /07/ **Estimated 95 perc prediction confidence interval (kg/m²/day) sounding1 sounding2 3A 3B 3C 4NA 4NB 4NC 4ZA 4ZB 4ZC 24/03/ /04/ /04/ /04/ /04/ /04/ /06/ /06/ /09/ /09/ NaN NaN NaN 23/10/ /12/ /12/ /02/ /04/ /05/ /05/ /06/ /06/ /07/ I/RA/11283/09.031/BOB page 20

27 Table 7: Comparison between measured and estimated sediment mass growth rates for different time periods (negative growth rates are excluded) (kg/m².day) 3A 3B 3C 4NA 4NB 4NC 4ZA 4ZB 4ZC measurement 08/ / < measured range 09/ / estimated range 03/ / I/RA/11283/09.031/BOB page 21