Kolgrafafjordur. Death of Herring v crossing of the fjord

Transcription

1 Kolgrafafjordur Death of Herring v crossing of the fjord

2 Crossing Influence Cause Culprit?

3 View north Kolgrafafjordur, Kjartan Pétur Sigurðsson 2004

4 View south Kolgrafafjord

5 The Crossing The outmost part is Urthvalafjordur, inside the crossing is Kolgrafafjordur. To the east of Urthvalafjordur, just outside the crossing, is Seljafjordur to Mjosund (narrow channel or strait) and then there is Hraunsfjordur. Reference (verbal): Gísli Karel Halldórsson Some people claim that the bridge across Mjosund is the first crossing in this country. 6

6 The Crossing. 7

7 The Crossing. 8

8 The Crossing 9

9 Crossing - measures The area of the basin (lagoon) inside the crossing is 10,2 km 2 The design aim for the level of the seabed in the water way opening was 8 m below Mean Sea Level The net or efficient area of the water way opening needed to be 1200 m 2 for mean current velocity of 2,5 m/sec at Mean High Water or 150 m wide. 10

10 Dýpi 11

11 Crossing typical measures A 230 m long bridge was built. Effective flow area 1264 m 2. Undisturbed tides were thus ensured. The length of the bridge is based on two criteria a. unhindered tides after crossing b. the average sea current through the opening should be 2,5 m/sec Criterium b is always the deciding one. For new crossing criterium b has been increased to 2,0 m/sec 12

12 Bridge over Kolgrafafjord 13

13 Seabed map: Kolgrafa-, Selja- og Hraunsfjords 14

14 Crossing typical measures A 230 m long bridge was built. Effective flow area 1264 m 2. Undisturbed tides were thus ensured. The length of the bridge is based on two criteria a. unhindered tides after crossing b. the average sea current through the opening should be 2,5 m/sec Criterium b is always the deciding one. For new crossing criterium b has been increased to 2,0 m/sec 15

15 Bridge over Kolgrafafjord 16

16 Crossings typical measures The effective flow area was based on the the effective length of the bridge and seabed at -8,0 m under mean sea level. The seabed was fine grained gravel and the current swept the gravel away and a equilibrium was reached -10,0 at the westmost span, at -11,0 in the centre span and at -9,5 m in the eastmost one. The rip-rap at the pillars did not perform as exspected. The foundatins are resting on the top of the piles some 3-4 m above the bottom of the seabet. 17

17 Crossings typical measures Due to this extra erosion the water way opening is somewhat larger than anticipated, approx. 300 m 2, and the velocity of the current proportionally less. The difference between Mean Low Water and Mean High Water just exceeds 4 m. 18

18 The Herring Story It has been stated that some t of herring were in Kolgrafafjord in in the end of year (Skessuhorn ) December 13 some t of herring were killed inside the crossing. February 1 additionl t were killed. Such events were unheard of. There is a story from 1941 about british soldiers who were fed on dead herring from the seaside. 19

19 The Herring Story The full effects on the marine live in Kolgrafafjord caused by this mass death of herring are still to be seen. The quota for herring catch of the fishingyear (sept-aug) var t The export value of t of herring is close to 7,7 Gkr (67 M USD$) 20

20 The cause of death Lack of oxygen is believed to be the cause of the herring death. It has been argued even stated that the small size of the bridge is to blame for that shortage of oxygen. (Wikipedia) The Marine Research Institute has decleared that the crossing did not have any role in this matter. Due to comments during the EIA-process of other crossings the tide were monitored both in Kolgrafafjord and Dyrafjord. 21

21 Tides and flows Mean sea level in Dyrafjord May 2011 was on average 0,03 m on the inside than the outside of the crossing. Mean sea level in Kolgrafafjord May 2011 was on average 0,04 m on the inside than the outside of the crossing. Conclusions: The tides are almost unchanged. The amount of sea flowing in and flowing out is therefore unchanged. But 22

22 Tides and flows Authorative individuals have discussed the removal of a part of the crossing in spite of unchanged flows. Bernoullie s law neglected. The cost of incorparating a 200 m wide and 3,5 m deep channel amounts to 1 Gkr or 9 MUS$ The local goverment and the roaduser in general disagree. Closing the road is not an optinon. The locals can accept closing the fjord completely and thus forming an unsalt lake with quite changed biology. 23

23 What s up - results? A consideable research has been carried out and is still being carried our by the Icelandic Road and Coastal Administration and the Marine Research Institute. It started in the spring of 2013 and MRI finished last June but IRCA will finish late next month. The purpose of the research was twofold: Firstly to establish what caused the lack of oxygen and secondly whether the crossing played a role therein or not. 24

24 What s up - results? Researchwork to establish current velocities, oxygen saturation, tidal hide of sealevels, sea temperature and degree of salt was carried out since spring 2013 to this summer Sea temperature and tide levels are still be monitored as well as heat radiation both into and out of the sea. 25

25 What s up results? Nothing, so far, gives any significant indication that the crossing has influenced the herring death. It is, on the other hand, clear that turbulances caused by the sea current in the bridge channel enhances the oxygen saturation. 26

26 Radiation measurements 27 Mælar

27 Few graphs and amen