Jimmy s beach preliminary results LP 668979 Jimmy s Beach Restoration Society 1
Outline 1. Long term: GIS analyses. Aerial photos, charts Shoreline analyses Storm data from MHL/DECC 2. Medium term: morphologic evolution. Topographic surveys 27, 28, 29 Wave data from MHL/DECC 3. Short term morphodynamics. Topographic surveys Wave and current measurements Summer and winter conditions Sediment characterisation
1. Long term trends From Thom et al. (1992) A spit was initiated about 17 years ago The spit reached hdits maximum length about 191 It was breached by storm in 1927 Landward reworking of sand to form a beach fronting Corrie Island 1795 1845 1866 199 192 1941 3
1. Long term trends Legend 9 m westward extension ~1 m retreat at erosion spot Spit1986 Spit1972 25 5 75 1, Meters
1. Long term trends Legend 1 m eastward retreat ~1 m retreat at erosion spot Spit1993 Spit1986 25 5 75 1, Meters
1. Long term trends Legend 6 m westward extension Small retreat at erosion spot Spit21 Spit1993 25 5 75 1, Meters
1. Long term trends Legend 6 m westward extension Small retreat at erosion spot Spit26 Spit21 25 5 75 1, Meters
1. Long term trends Legend 14 m westward extension ~1 m retreat at erosion spot Spit28 Spit26 25 5 75 1, Meters
1. Long term trends Legend Spit29 Spit28 No westward extension Retreat in WW 25 5 75 1, Meters
1. Long term trends Legend Spit29 Spit28 Spit26 Spit21 Spit1993 Spit1986 Spit1972 Spit1951 8 m westward extension (14 m/a) /) Retreat up to 12 m in WW (2 m/a) Retreat up to 95 m in JB (1.6 m/a) 25 5 75 1, Meters
1. Long term trends 1968 1986 1993 25 5 75 1, Meters 25 5 75 1, Meters 25 5 75 1, Meters Cholinski et al. (24) First sandwave in the 8s Landward migration 7m/yr between 1993 23 21 26 25 5 75 1, Meters 25 5 75 1, Meters
1. Long term trends Map from Darwin s exhibition showing map from circa 1836 (photo by J.Benavente).
1. Long term trends 1968 1986 1993 21 26 28 Transect evolution rates (m/yr r) 2 15 1 5-5 -1-15 -2 T1 T2 T3 T4 T5 T6 T7 T8 T9 T1 T11 68-86 86-93 93-1 1-6 6-8 1968 to 1986: overall oea accumulation u a 1986 to 1993: erosion on sides and accumulation on centre 1993 to 21: overall accumulation 21 to 26: accumulation T1 T4 and erosion in others 26 to 28: erosion in T1 T4 T4 and accumulation in others
1. Long term trends Our data show two periods: Initial accumulation and westward migration (until mid 199s) Slow migration/ stabilisation continuous presence of seagrass west from the sandwave. Legend After the dredging Sandwave29 Sandwave28 Sandwave26 Sandwave1963 25 5 Meters
2. Medium term evolution Topographic surveys of Jimmy s beach started in March 27. 24 March 27 26 May 27 19 June 27 23 July 27 Topographic profiles 12 October 27 Digital terrain models 28 November 27 15 February 28 Morphologic comparisons 9 April 28 Volumetric calculations 28 October 28
2. Medium term evolution Significant Wav ve Height (m) 8 6 4 2 Apr27 Jun27 Jul27 Sep27 Nov27 Dec27Feb28 Apr28 Significant Wa ave Period (s) 1 5 Apr27 Jun27 Jul27 Sep27 Nov27 Dec27Feb28 Apr28 Wave Dire ection (deg) 36 27 18 9 Apr27 Jun27 Jul27 Sep27 Nov27 Dec27Feb28 Apr28 Time
2. Medium term evolution x 1 5 4 3 2 (7-18degN) (N/ms) 1 Apr7 Jul7 Oct7 Jan8 Apr8 Time Wave Power
2. Medium term evolution Elevation (m) 2.5 2 1.5 1.5 Profile1 73 75 76 77 71 711 84 Elevation (m) 3.5 3 2.5 2 1.5 1.5 Profile1 73 75 76 77 711 82 84 -.5 -.5-1 -1-1.5-1 1 2 3 4 5 6 7 8 9 Distance (m) Large erosion March May 27. Overall accumulation. Elevation (m) 5 4 3 2 1 Profile4 73 75 76 77 71 711 82 84 Elevation (m) 4 3 2 1 Profile6 73 75 76 77 71 711 84-1.5-1 1 2 3 4 5 6 7 Distance (m) Evolution dominated by sandwave processes. -1-1 -2-1 -5 5 1 15 2 25 3 Distance (m) Emergency nourishment placed enough sediment to counteract storm erosion. -2-5 5 1 15 2 25 3 Distance (m) Relatively stable part of the beach. Final accumulation due to pipeline burial.
2. Medium term evolution Northings (m) Wave Power (7-18deg gn) (N/ms) 4 x 15 3 2 1 Apr7 Jul7 Oct7 Jan8 Apr8 Time (m) 63845 6384 63835 6383 77711evol.mat 63845 2 6384 63835 6383 63825 Northings 63825 1.5 7375evol.mat 1 6382 421 4215 422 4225 423 4235 424.5 Eastings (m) -.5 5-1 -1.5 Low energy e gyso stormss Overall erosion 2 1. 1. - -1-1 -2 6382 421 4215 422 4225 423 4235 424-2 Eastings (m)
2. Medium term evolution Severe and extreme storms ms) Wave Powe er (7-18degN) (N/ 4 x 15 3 2 1 Apr7 Jul7 Oct7 Jan8 Apr8 Time
2. Medium term evolution 63845 7576evol.mat 2 7677evol.mat 2 1.5 1.5 6384 1 1 (m) Northings ( 63835 6383.5 -.5.5 -.5 63825-1 -1-1.5-1.5 6382 421 4215 422 4225 423 4235 424 1-2 4215 422 4225 423 4235 424 Eastings (m) Eastings (m) 4 x 15 gn) (N/ms) e Power (7-18de Wav 3 2 1 Apr7 Jul7 Oct7 Jan8 Apr8 Time Severe and extreme storms Overall accumulation on sandwave with development of transverse bars -2
2. Medium term evolution 63845 7384evol.mat 2 1.5 BEFORE NOURISHMENT: North hings (m) 6384 63835 6383 1 Overall volumetric evolution.5 (thousands of cubic metres): Beach: 52 Sandwave: +1 -.5 63825-1 -1.5 Total: 42 6382 421 4215 422 4225 423 4235 424-2 Eastings (m)
2. Medium term evolution 63845 7381evol.mat 2 AFTER NOURISHMENT: North hings (m) 6384 63835 6383 1-1 Overall volumetric evolution (thousands of cubic metres): Beach: +13 Sandwave: 5-2 63825-3 Total: 37 6382 421 4215 422 4225 423 4235 424-4 Eastings (m)
3. Short term morphodynamics 5 4 3 2 Sandwave Winda Woppa Spit Erosion spot 1 25 5 1, Meters 25 5 1, Meters
3. Short term morphodynamics Hydrodynamic measurements taken in 27 and 28: March 27: fair weather conditions and southerly change. June 27: SE storm and strong westerly conditions. March/April 28: fair weather with NE, SE and westerlies. 766 files containing 15 minutes of currents and waves
3. Short term morphodynamics Preliminary analyses have been undertaken by honours students (Ainley and Pezzimenti) and we are now re processing all the data to make sure that is all analysed according to the same standards and we are also starting to implement some sediment transport calculations. We are calculating: 15 minutes averages of current velocities and direction Percentages of sediment entrainment
3. Short term morphodynamics.1 ADVJB7324.txt.1 ADVJB7325.txt 5.5 5.5 -.5 -.1 Across-shore, +on/-off Alongshore, +west/-east east 12: 13: 14: 15: -.5 -.1 Across-shore, +on/-off Alongshore, +west/-east east 9: 12: 15: 1 Critical velocity (m/s) Percentage of entrainment (%) 1 Critical velocity (m/s) Percentage of entrainment (%) 5 5 12: 13: 14: 15: JB3 Fair weather Winda Woppa Spit Erosion spot 9: 12: 15: Sandwave JB2 Southerly 25 5 1, Meters
3. Short term morphodynamics Winda Woppa Spit Erosion spot 1 8:3 Sandwave March 27: Southerly waves (Ho=1.97m) and ebbing currents result on eastwards currents..1.5 -.5 ADVJB7327.txt Across-shore, +on/-off Alongshore, +west/-east -.1 8:45 9: 9:15 25 5 1, Meters 1 25 5 1, Meters.1 842JB1S.txt 5 Critical velocity (m/s) Percentage of entrainment (%).5 8:3 8:45 9: 9:15 April 28: SE waves (Ho=1.5m). Low tide at 12h, westerly currents with flooding. -.5 -.1 1 5 Across-shore, +on/-off Alongshore, +west/-east 9: 12: 15: 18: Critical velocity (m/s) Percentage of entrainment (%) 9: 12: 15: 18: Effects of refraction on sand shoals and preferred tidal channels
3. Short term morphodynamics Winda Woppa Spit Erosion spot 2 Sandwave March 27: Southerly waves (Ho=2.63m). High tide at 12:43h. Currents remain westward independent from the tide. ADVJB7325.txt.1.5 -.5 -.1 9: 12: 15: Across-shore, +on/-off Alongshore, +west/-east 25 5 1, Meters 25 5 1, Meters.1.5 June 27: Strong westerly conditions. Wind waves developing (high tide at 13:24h). Westward currents -.5 -.1 1 5 ADVJB7621.txt Across-shore, +on/-off Alongshore, +west/-east 9: 1: 11: 12: 13: 14: 15: Critical velocity (m/s) Percentage of entrainment (%) 1 5 Critical velocity (m/s) Percentage of entrainment (%) 9: 12: 15: Fair weather conditions tidal current prevail. 9: 1: 11: 12: 13: 14: 15:
3. Short term morphodynamics March 27: westward currents under fair weather conditions. High tide at 12:43h. Sandwave ADVJB7324.txt 3.1.5 Winda Woppa Spit Erosion spot -.5 -.1 Across-shore, +on/-off Alongshore, +west/-east 12: 13: 14: 15: 25 5 1, Meters 1 Critical velocity (m/s) Percentage of entrainment (%) 25 5 1, Meters 5 March 28: westerly development and flooding currents (HT~17h) result in eastward currents..1.5 -.5 -.1 1 5 8331JB3S.txt Across-shore, +on/-off Alongshore, +west/-east 9: 12: 15: 18: Critical velocity (m/s) Percentage of entrainment (%) 12: 13: 14: 15: This area seems stable. 9: 12: 15: 18:
3. Short term morphodynamics Winda Woppa Spit 4 Erosion spot Sandwave March 28: Fair weather conditions, no waves, no wind, HT ~16h. Wave arriving normal to the shore, negligible alongshore currents..1.5 833JB4S.txt Across-shore, +on/-off Alongshore, +west/-east -.5 25 5 1, Meters -.1 9: 12: 15: 18: 25 5 1, Meters April 28: Ho>1m; LT~14h. Waves arriving shore normal, no clear alongshore currents. Stops after LT..1.5 844JB4S.txt -.5 Across-shore, +on/-off Alongshore, +west/-east -.1 6: 9: 12: 15: 18: 1 5 1 5 Critical velocity (m/s) Percentage of entrainment (%) 9: 12: 15: 18: Critical velocity (m/s) Percentage of entrainment (%) 6: 9: 12: 15: 18:
3. Short term morphodynamics 5 Winda Woppa Spit Erosion spot Sandwave March 28: wind waves developing before 12h coincident with flooding. Resultant currents are eastwards..1.5 8331JB5N.txt Across-shore, +on/-off Alongshore, +west/-east -.5 -.1 9: 12: 15: 18: 25 5 1, Meters 25 5 1, Meters April 28: no wind, no waves, only tidal currents. LT at 12h..1.5 -.5 841JB5N.txt Across-shore, +on/-off Alongshore, +west/-east -.1 9: 12: 15: 18: 1 Critical velocity (m/s) Percentage of entrainment (%) 1 5 Critical velocity (m/s) Percentage of entrainment (%) 9: 12: 15: 18: 5 9: 12: 15: 18:
3. Short term morphodynamics We are still re processing all data but there are some preliminary findings: Sector 1 is very shallow and currents seem related to refraction and tidal channels. Sector 2 experiences westward currents with sediment entrainment both under westerly and southerly conditions. Reversing tidal currents prevail under fair weather conditions. Sector 3 has eastward currents with sediment entrainment under westerly conditions. Westward currents with no entrainment occur under fair weather conditions. Sector 4 often experiences shore normal waves, alongshore currents are small and change direction. Sector 5 has small eastward currents with no entrainment during most of the time.
4. What is going on? There are evidences of westward sediment transport in the decadal and medium term studies: Westward extension of Winda Woppa. Sandwave evolution. The short term studies show that eastward currents with sediment entrainment occur under westerly conditions in some parts of the beach. They show, however, that under higher energy SE conditions, the transport is to the west. More analyses and links to other results from the project (FTDand numerical modeling) willhelpestablishing establishing what is going on.