The study examines the shoreline (1990-2019) and nearshore morphological changes (seasonal) to understand the littoral drift and sediment budget variability. Shoreline change rate depicts erosion (-0.06 m/yr) in the northern sector and accretion (+0.12 m/yr) in the southern sector. Seasonal nearshore morphological changes from non-monsoon to monsoon period signifies net erosion (-1.8x10^4 m^3 ) in northern sector and net accretion (+2.5x10^4 m^3) in the southern sector. Although the lost sediment during monsoon is regained in non-monsoon period, the quantity of sediment gain is reduced in areas with human interventions. The results of the investigation depict the dominance of littoral drift towards north from February to October, when wave approach from east-southeast to south-southeast direction and southwards from November to January when the wave direction was from east-northeast to east-southeast. The net longshore sediment transport rate estimated during the study period was 2.6x10^5 m^3/year in the northern sector and 1.5x10^5 m^3/year in the southern sector with higher rate attributed to monsoon than the non-monsoon. Sediment budget results in deciphering the causes of erosion (-1.27×10^4 m^3/yr) in northern sector and accretion (3.91×10^4 m^3/yr) in southern sector in the wave-dominated Chennai beach.
Research Article
Implication of Shoreline and Nearshore Morphological Changes on Sediment Budget of Wave-Dominated Chennai Beach, India
https://doi.org/10.21203/rs.3.rs-1045828/v1
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Shoreline
Nearshore morphology
Longshore sediment transport
Sediment budget
Chennai
Table 1
Details of satellite data used in the study and occurrence of natural calamities from 1990-2019
|
Year |
Data (resolution) |
Source |
RMSE |
Natural calamities |
|
1990 to 2000 |
Landsat TM (30 m) |
United States Geological Survey (USGS) Earth Explorer |
18 m |
Depression BOB 07 (1991), Cyclonic Storm BOB 08 (1991), Severe Cyclonic Storm BOB 03 (1994), Very Severe Cyclonic Storm BOB 06 (1996) |
|
2000 to 2006 |
Landsat ETM+ (30 m) |
16.7 m |
Extremely Severe Cyclonic Storm BOB 05 (2000), Cyclonic Storm BOB 02 (2001), Indian Ocean Earthquake and Tsunami (2004), Cyclonic Storm Fanoos (2005) |
|
|
2006 to 2012 |
Cartosat-1 (2.5 m) |
National Remote Sensing Centre (NRSC) Data Centre |
2 m |
Cyclonic Storm Nisha (2008), Severe Cyclonic Storm Jal (2010), Very Severe Cyclonic Storm Thane (2011) |
|
2012 to 2019 |
Resourcesat–II LISS IV (5.8 m) |
2.2 m |
Cyclonic Storm Nilam (2012), Very Severe Cyclonic Storm Madi (2013), Deep Depression BOB 03 (2015), Very Severe Cyclonic Storm Vardah (2016) |
Table 2
Seasonal variation in the cross-sectional area (m2 ) and changes (%) along the northern and southern sector
Table 3
Seasonal variation in the volume (m3 ) and changes (%) along the northern and southern sector
Table 4
Seasonal changes in beach slope, median grain size and sediment type in the study site
|
Sector |
Transect |
April 2019 |
September 2019 |
December 2019 |
||||||
|
Beach slope |
D50 (µm) |
Sediment type |
Beach slope |
D50 (µm) |
Sediment type |
Beach slope |
D50 (µm) |
Sediment type |
||
|
Northern |
P1 |
1:50 |
555.2 |
Coarse Sand |
1:50 |
413.6 |
Medium Sand |
1:33 |
532.7 |
Coarse Sand |
|
P2 |
1:50 |
528.6 |
Coarse Sand |
1:50 |
392.8 |
Medium Sand |
1:25 |
354.0 |
Medium Sand |
|
|
P3 |
1:20 |
588.9 |
Coarse Sand |
1:20 |
375.1 |
Medium Sand |
1:14 |
349.4 |
Medium Sand |
|
|
P4 |
1:10 |
580.5 |
Coarse Sand |
1:7 |
437.7 |
Medium Sand |
1:6 |
551.7 |
Coarse Sand |
|
|
P5 |
1:100 |
432.7 |
Medium Sand |
1:50 |
458.8 |
Medium Sand |
1:50 |
637.7 |
Coarse Sand |
|
|
Southern |
P6 |
1:100 |
401.8 |
Medium Sand |
1:100 |
432.8 |
Medium Sand |
1:100 |
587.1 |
Coarse Sand |
|
P7 |
1:100 |
536.6 |
Coarse Sand |
1:100 |
403.7 |
Medium Sand |
1:50 |
589.2 |
Coarse Sand |
|
|
P8 |
1:20 |
609.5 |
Coarse Sand |
1:20 |
383.0 |
Medium Sand |
1:20 |
397.0 |
Medium Sand |
|
|
P9 |
1:50 |
352.9 |
Medium Sand |
1:50 |
419.5 |
Medium Sand |
1:50 |
468.1 |
Medium Sand |
|
|
P10 |
1:25 |
618.0 |
Coarse Sand |
1:20 |
372.3 |
Medium Sand |
1:17 |
700.5 |
Coarse Sand |
|
Table 5
Monthly average of the significant wave height, wave direction, and wave period along the Chennai coast
Months |
Significant Wave Height (m) |
Wave Direction (deg) |
Wave Period (s) |
|
January |
0.78 |
92 |
4.34 |
|
February |
0.68 |
108 |
4.55 |
|
March |
0.68 |
129 |
4.46 |
|
April |
0.73 |
131 |
4.85 |
|
May |
1.03 |
141 |
4.74 |
|
June |
1.06 |
149 |
5.14 |
|
July |
1.01 |
146 |
5.19 |
|
August |
1.01 |
146 |
5.39 |
|
September |
0.89 |
135 |
5.39 |
|
October |
0.75 |
127 |
5.00 |
|
November |
0.96 |
84 |
4.70 |
|
December |
1.21 |
99 |
4.74 |
Table 6
Longshore sediment transport rate (m3 ) estimated at selected transects along the northern and southern sector
|
Sector |
Transect |
Longshore sediment transport rate (m3) |
Net (m3/yr) |
Gross (m3/yr) |
|||||||||||
|
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
||||
|
Northern |
P1 |
-1485 |
686 |
1788 |
2351 |
4540 |
5602 |
5454 |
5819 |
4434 |
3484 |
-4268 |
-2717 |
25690 |
42630 |
|
P2 |
-1179 |
992 |
1887 |
2462 |
4554 |
5472 |
5380 |
5752 |
4555 |
5042 |
-5204 |
908 |
30621 |
43387 |
|
|
P3 |
-2614 |
1653 |
3585 |
4696 |
8870 |
11228 |
10985 |
11732 |
9115 |
7520 |
-8478 |
-3551 |
54742 |
84027 |
|
|
P4 |
-3851 |
3241 |
6164 |
8042 |
14874 |
24136 |
23733 |
25372 |
20091 |
12764 |
-13174 |
2299 |
123692 |
157742 |
|
|
P5 |
-309 |
350 |
602 |
782 |
1418 |
5139 |
5080 |
5436 |
4386 |
2636 |
-2470 |
1471 |
24520 |
30078 |
|
|
Southern |
P6 |
-1253 |
-354 |
989 |
1330 |
2849 |
3393 |
3237 |
3440 |
2406 |
1244 |
-2108 |
-2276 |
12895 |
24878 |
|
P7 |
-1138 |
-265 |
944 |
1265 |
2668 |
3450 |
3301 |
3509 |
2484 |
2154 |
-3498 |
-3641 |
11233 |
28316 |
|
|
P8 |
-3380 |
439 |
3260 |
4330 |
8770 |
11607 |
11189 |
11914 |
8717 |
5101 |
-7331 |
-6624 |
47992 |
82663 |
|
|
P9 |
-1663 |
768 |
2002 |
2633 |
5085 |
5583 |
5435 |
5799 |
4419 |
2655 |
-3252 |
-2070 |
27393 |
41364 |
|
|
P10 |
-2312 |
1257 |
2964 |
3889 |
7427 |
11347 |
11074 |
11821 |
9096 |
5554 |
-6530 |
-3527 |
52062 |
76798 |
|
(+) Northwards; (-) Southwards