Extra material

Some cases of internal erosion
during the floods of 2005 and
2006 in Romania
by Iulian ASMAN - RWNA
Significant reservoirs: 400
Stored volume: 13,070 mill. cu.m
Water derivations:
derivations: 1490 km
Embankments and riverbed
regulations works: 18,240 km
Protected area: 2.13 mil. ha
Localities: 1927
Social and economic units: 3100
Roads and railways: 6100 km
Draining works: 3.2 mill. ha
Soil erosion protection works:
2.27 mill. ha
5500 (RECOVER.)
4650 (REGIST.)
– JULY 2005 2800 – AUGUST 2005
2OOO – JUNE 2005
1250 – APRIL 2005
1332 – SEPT 2005
Actual stage of flood protection works
67 114
W.D.
1680
W.D.
CRISURI
130 226
1780
SOMESTISA
TOTAL
129 415 1738
1419
3716
15,701
W.D.
W.D.
SIRET PRUT
Nr.
31 194
W.D. MURES
1495
Mil. mc.
mc.
Km.
308 2067
798
54 242
W.D.
2095
W.D.
OLT
BANAT
W.D. JIU
50 177 890
191 113
1666
W.D. IALOMITA
-BUZAU
W.D.
ARGES
-VEDEA
77
29
715
W.D.
DOBROGEA
LITORAL
224 104
384
36
35
138
PeakPeak-flow mitigation
reservoirs (no
(no.)
Attenuation volumes in
reservoirs (mill. cu.m)
cu.m)
Structures on watercourses
(km.)
Damages caused by flooding during 1992-2005 period
5,000
586.0
TOTAL 1992-2004:2,958.1 mil. lei
425.3
362.3
333.2
mil. lei
292.7
235.2
221.8
258.8
95.8
41.1
1992
16.5
1993
52.0
1994
37.4
1995
1996
1997
Years
1998
1999
2000
2001
2002 2003
2004
2005
Counties’ vulnerability degree at floods
1992-2004
29 %
BOTOSANI
SATUMARE
Dm<30
MARAMURES
Dtot<250
SUCEAVA
BIHOR
SALAJ
BISTRITANASAUD
IASI
33 %
Dm>70
Dtot>750
NEAMT
CLUJ
28 %
Dm=30-50
Dtot=250-450
MURES
HARGHITA
ARAD
BACAU
ALBA
TIMIS
VASLUI
COVASNA
SIBIU
HUNEDOARA
VRANCEA GALATI
BRASOV
BUZAU
CARAS
-SEVERIN
VALCEA
GORJ
PRAHOVA
ARGES
DAMBOVITA
ILFOV
MEHEDINTI
BUCHAREST
DOLJ
OLT
TELEORMAN
10 %
Dm=50-70
Dtot=455-750
GIURGIU
BRAILA
TULCEA
Dm – Mean evaluated damages
(bil.
bil. old lei)
DtotDtot- Total evaluated damages
(bil.
bil. old lei)
IALOMITA
CALARASI
CONSTANTA
Counties with very high vulnerability degree
Counties with high vulnerability degree
Counties with mean vulnerability degree
Counties with low vulnerability degree
Strong affected zones by 2005 floods
Introduction
One of the regions most affected by the floods of 2005 in Romania was
Lower Siret river basin where heavy rains were recorded between 8
and 17 of July, 2005.
The Ministry of Environment and Water Management (MEWM)
estimated that this flooding was a 500 to 1000 year event and caused
more than Eur20M in damage.
Inspection of some of the selected levees
A group of experts including representatives of US Army Corps of
Engineers and of Romanian central and local water authorities
inspected the area in order to assess damage and to issue
recommendations concerning hydraulic structure failures and
reconstruction effort. We will present below two of the sites inspected
during this task mission.
Site A – Controlled breach of the levee for stepping up drainage
to the river
The levee section was cut by an intentional breach carried out for
draining water to the nearby Siret River in an area previously
weakened by leakages in various points. The cut section was
approximately 7 meters wide with very steep side walls.
Figure A.1 – Map of Eastern Romania and close – up map showing this site location
This site was situated next to a pumping station belonging to the land
improvement company (see figure 2) which was flooded. The levee
breach location may also have been the location where the pipes went
through the levee embankment to the other side. Consequently, this
location probably experienced some localized internal erosion and was
starting to generate levee failure.
Figure A.2 – The levee breach and the nearby old pump station building
Site B – Internal erosion failure along a pipe going through the levee
embankment
This levee failed due to internal erosion of soil along the outside of the
pipe that crossed the middle of this levee (see figures below).
Figure B.1 – Overview of the levee failure caused by internal erosion along outside of
a pipe crossing the levee
Figure B. 2 Map of Eastern Romania and close-up map showing this site location
Figure B.3 – Satellite photo showing a segment of the affected river system.
This levee.
Description of the failure
- Initially, a 2 cm diameter of leakage was observed flowing out along the
outside of the pipe for several hours.
-Eight hours after the initial observation the leakage flow had a diameter
of 20 cm.
- At ten hours after the initial seepage observation, the water was flowing
out from the whole area of the pipe diameter.
- At twelve hours, the levee crest collapsed.
Potential causes of the failure
- A structural foundation shown in Figure B.1 was apparently used to
support the pipe that went through the levee. The levee foundation is a
stiff medium to soft soil composed of clayey silts to silty clays.
- After the levee was built, it experienced settlement due to
consolidation of the foundation soil and compression of the levee
material. A foundation support for the horizontal pipe will create
differential settlement between the pipe and surrounding levee soils.
- There was potential for a void to form or low stress condition to develop
along the bottom side of the horizontal pipe.
- If the horizontal pipe floats inside the levee material, the pipe will still
experience differential settlement due to high settlement in the middle of
the levee compared to no settlement at the levee embankment toes.
-There is also potential for leakage from the inside pipe (under high
water pressure) and through the pipe joints to the soil adjacent to the
pipe.
- The biggest factor is the potential for erosion, soil mixtures which are
primarily silt are the biggest problem, and this is the primary soil type
used for levees in this part of Romania. If the levee soil has a high
erosion potential then pipes should not be constructed to cross the
levees.
Remedial techniques
- The high velocity flow and large volume of water that passed this
breach area has generated a very deep void within natural soils. Filling
the gap in such situations is not that simple as excavating to the natural
soils followed by placing fill soil in lifts. The deep void (into the natural
soil) has to be excavated and filled with material that is similar to the soil
in the non failed levee sections.
Figure B.4 Cutting
methods for two
possible repairing
situations:
the breach affects
only the levee;
- the breach gap is
cut in the natural
soil.
-The first task is to cut the non affected levee to a very shallow slope.
If the If the void is deep it might be required to remove part of the
existing levee next to the void for at least a distance equal to 1.5 the
void depth (see figure B. 4). Initially, a ring dike needs to be
constructed to prevent outside water from reentering the void.
-The void will then need to be pumped out of water. Because of the
potential depth of the void, there might be potential for side slope
failures into the void from the existing levee and even from the level
ground areas. Soft and loose material must be removed from the void
to expose the natural soil.
-The next stage is to compact natural soil back into the void at
densities approximately equal to the densities under the existing
levee. If the replaced natural soil is too stiff then there might be
potential for differential settlement after the levee is finally finished.
SITUATION OF THE MOST AFFECTED ZONES IN 2006
SIRET
SOMES TISA
03-07martie
25.martie-02 aprilie
27 mai-03 iunie
Inundatii fulger
CRISURI
-MARTIE-MAI-IUNIEDEPASIRI FAZA III
FARA PAGUBE
SEMNIFICATIVE
BANAT
-25.02.-04.03DEPASIRI FAZA II
FARA PAGUBE
SEMNIFICATIVE
JUD. SUCEAVA
-3030-31 iunie 20062006Inundatii fulger
6 victime,
victime, 8 disparuti
SOMES-TISA
TARLISUA SI ALTE 12
LOCALITATI
1919-21.06.2006
CAUZE: INUNDATII FULGER
11persoane decedate
PRUT
16-26 iunie
OANCEA AVAL
Cresteri de nivel rau Prut
Pagube datorate in
special scurgerilor pe
versanti
JIU
-13-14 martie 2006Inundatii “fulger”
Zones where significant water level growths on the main rivers were recorded
Zones where “flash floods” without casualties were recorded
Zones where “flash floods” with casualties were recorded
Zones affected along the Danube
MURES
Martie, Iunie
Inundatii fulger,
Nu sunt inregistrate victime
DUNARE
-15 martiemartie-15 maimaiDEPASIREA COTELOR ISTORICE
Nu au fost inregistrate victime
DANUBE 2006
Ceatalchioi,
25.04.2006, ora 18.00
Breaches generated by failure
Isaccea
Bresa închisă,
10.04.2006, 11.00
Breaches achieved for discharging
Ostrov,
26.04.2006, ora 19.40
Breaches achieved for mitigation
Făcăieni
Inundare controlata,
15.04.2006, 19.00
Obretin,
20.04.2006, ora 12.00
Călăraşi-Râul
Inundare controlată
17.04.2006, 16.00
Spanţov,
23.04.2006, ora 14.30
Cardon,
24.04.2006, ora 7.00
Rast, 14.04.2006, ora 11.30
Channel Împuţita
Cresa controlata
21.04.2006, 14.00
Bistreţ, 24.04.2006, ora 7.50
Bechet, 24.04.2006, ora 7.15
Tatina,
3.05.2006, ora
11.10
Mănăstirea, 2.05.2006, ora 17.10,
bresa pentru evacuare
Nedeia, 3.05.2006
Ora 15.41, breaches for water
evacuation
Oltina,
22.04.2006,
ora 17.00
The Isaccea Breach
The breach of Isaccea on the Chilia branch of the Danube Delta
appeared and developed very quickly. In less than 30 minutes the levee
collapsed on a 20 m wide zone. The cause of this unwanted event was
the presence in the levee of an unknown old culvert taken out of service.
The pipe generated in the conditions of a prolonged hydrostatic loading,
the internal erosion phenomenon due to differentiated settlement.
The breach was provisionally closed in 24 hours. At present are
underway final repairings.
Breach of Spantov
The Spantov phenomenon
The reeds growing on the levees in this area were mowed on a
regular basis but only at the surface level, so that the roots got
stronger and thicker up to 1.5 m deep.
The phenomenon of internal erosion generated the sliding on 23rd
of April 2006 of the downstream face on a 30 m wide area. It was
attempted the stabilization of the levee with 15,000 sandbags
placed at the downstream toe and the covering of the sliding zone
with geo-membrane for reducing the driving out of construction
material from the levee, but apparently without much success.
The levees in this area as well as along most of the Danube are
administered by a land reclamation company. They are in the
process of being fixed.
Excavation down to natural soil before start of fill
-The natural soils (under the levees) are stronger than the recently
deposited soils.
-Visual inspection is all that is required to verify the natural soil
elevation.
-The best means of differentiating soft transported soil and the
natural soils is with a hand probe (and an experienced operator).
Figure C.1 Excavation of soft transported soil is required down to the
natural soil
Excavation of transported soil is important for two reasons:
1) to remove potentially sandy soil which could produce internal erosion
failure;
2) to remove soft unconsolidated clays which will cause structural
embankment failure.
-Some breach area shapes will produce channels of sands and silts.
Water moving through the breach gap can drop sediments into the gap,
based on the water velocity.
- There is a real potential for a channel of sand to be generated from
the levee toe on the land side to the levee toe on the river side. A single
sand channel under a levee can generate internal erosion.
Piping issues
Placing pipes through levees is bad practice (Figure C.2). There is
worldwide history of failures due to internal erosion along the outside of
buried pipes in embankments.
-The causes for failure are settlement, differential movement,
compaction problems, structural problems, and a soil that can erode
(silt).
-The best practice is not to allow pipes through embankments. If a pipe
must be placed inside a levee embankment then there are numerous
specifications which must be followed.
-Internal soil erosion along the outside of pipes is caused by the
generation of “pipes of water.“ Pipes are difficult to properly place into
embankments. Compaction of the soil along the bottom of the pipe is
difficult to do in practice because the pipe must be placed onto the
compacted soil. Compaction of soil onto the top half of the pipe is much
easier.
Figure C. 2 Pipes through levees is not a good practice
- Historically, researchers have believed that the primary cause for
internal soil erosion along the outside of pipes was because of issues
related to compaction of the soil around the pipe.
- However, the major issue is differential settlement (or the strain
caused by the tendency for differential settlement). Differential
settlement can be due to soil type changes or material type changes,
or soil to concrete or soil to rock issues. Ultimately, internal erosion
can only occur if the soil has erosion potential, such as high silt content
soil mixtures.