Studies regarding the safety in operation of Râpa Albastră reservoir Studii privind siguranţă în exploatare a acumulării Râpa Albastră

Abstract

The dam of Râpa Albastră reservoir, located on Simila River, is an earth dam with a maximum height of 17.80 m, which provides a global retention to the canopy of 23.159 million cubic meters. Râpa Albastră reservoir is a part of the hydrotechnical works set that were built to protect against the floods Bârlad, Vaslui, Tecuci cities and other villages in Bârlad catchment area. During the years 2008÷2011 investment works were implemented, under the project "Safety reinforcement of Râpa Albastră reservoir, located on the Simila River, in Vaslui county". The project was set out to build the following works: revegetation on the downstream slope of the dam, restoring transport capacity of the bottom outlet channel, calibration of Simila River bed over a length of approximately 1240 m, repairs to the access bridge from the canopy to the operation tower, repairs to the operation tower cabin, rehabilitation of the hydro-mechanical equipments, electrical installations, water management information and warning-alarm system, driveway restoration to the dam canopy. This paper presents a brief history of the dam and aspects regarding the behaviour monitoring of Râpa Albastră reservoir during the years 1997-2012.

Full text

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Studies regarding the safety in operation of Râpa Albastră reservoir
Studii privind siguranţă în exploatare a acumulării Râpa Albastră
Isabela BALAN1, Claudiu PRICOP2, Ioan BALAN2, Dan BURUIANĂ2
1 “Gheorghe Asachi” Technical University of Iasi, Faculty of Hydrotechnics,
Geodesy and Environmental Engineering, Romania
2 Water Basinal Administration Prut-Bârlad, Romania
isabela.balan@yahoo.co.uk
Abstract: The dam of Râpa Albastră reservoir, located on Simila River, is an earth dam with a
maximum height of 17.80 m, which provides a global retention to the canopy of 23.159 million
cubic meters. Râpa Albastră reservoir is a part of the hydrotechnical works set that were built to
protect against the floods Bârlad, Vaslui, Tecuci cities and other villages in Bârlad catchment
area. During the years 2008÷2011 investment works were implemented, under the project „Safety
re-inforcement of Râpa Albastră reservoir, located on the Simila River, in Vaslui county”. The
project was set out to build the following works: revegetation on the downstream slope of the dam,
restoring transport capacity of the bottom outlet channel, calibration of Simila River bed over a
length of approximately 1240 m, repairs to the access bridge from the canopy to the operation
tower, repairs to the operation tower cabin, rehabilitation of the hydro-mechanical equipments,
electrical installations, water management information and warning-alarm system, driveway
restoration to the dam canopy.
This paper presents a brief history of the dam and aspects regarding the behaviour monitoring of
Râpa Albastră reservoir during the years 1997-2012.
Keywords: access bridge, safety re-inforcement, hydrostatic level, behaviour monitoring
Rezumat: Barajul acumulării Râpa Albastră, amplasat pe râul Simila, este un baraj de pământ cu
o înălţime maximă de 17,80 m, care realizează o retenţie globală la cota coronamentului de
23,159 milioane mc. Acumularea Râpa Albastră face parte din ansamblul de lucrări prevăzute
pentru combaterea inundaţiilor din bazinul hidrografic al râului Bârlad şi are ca efect apărarea
oraşelor Bârlad, Vaslui, Tecuci, şi alte localiăți rurale din luncă. În perioada 2008÷2011 la
acumularea Râpa Albastră au fost implementate lucrări de investiţii în cadrul proiectului „Punerea
în siguranţă a acumulării Râpa Albastră, judeţul Vaslui”. Proiectul a prevăzut realizarea
următoarelor lucrări: refacerea covorului vegetal de pe paramentul aval, refacerea capacităţii de
transport aval baraj pe canalul de fund, regularizare albie curs apă Simila, pe o lungime de cca.
1240 m, refacere pasarelă de acces la turnul de manevră, reparaţii la cabina turnului de manevră,
reabilitare echipament hidromecanic, instalaţii electrice, sistem informaţional de gospodărire a
apelor şi avertizare - alarmare, refacere drum de acces la coronament.
Lucrarea prezintă un scurt istoric al barajului şi aspecte privind urmărirea comportării în timp a
acumulării Râpa Albastră în perioada 2000-2012.
Cuvinte cheie: pasarelă de acces, punere în siguranţă, nivel hidrostatic, urmărirea comportării
INTRODUCTION
Râpa Albastră reservoir, operated by Water Basinal Administration Prut-Bârlad, is located on
Simila River (cadastral code XII.1.78.29), a right tributary of Bârlad River, at about 3,25 km upstream
of the confluence, in Zorleni village, Vaslui county. The reservoir commissioned in 1975 has the
following functions:
- it contributes, along with other hydrotechnical works in the area, to the protection
against floods for downstream settlements in the valleys of Bârlad River and Simila
River and mainly for Bârlad and Tecuci cities. It also protects against floods the
downstream industrial area, the paths of communication (railway "Tecuci – Iaşi,
European 581 Albiţa-Crasna-Tişiţa, etc.);
- water supply for the industrial area of Bârlad city;
- irrigation;

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- fishing;
- salubrious flow downstream of the dam.
Retention in Râpa Albastră reservoir is made by a frontal dam with a canopy length of 810 m,
and a width of 6.0 m.
REHABILITATION WORKS
During the years 2008÷2011 investment works were implemented, under the project „Safety
re-inforcement of Râpa Albastră reservoir, located on the Simila River, in Vaslui county”.
The project was set out to build the following works:
- hydrotechnical works (revegetation on the downstream slope of the dam, restoring
transport capacity of the bottom outlet channel, calibration of Simila River bed over a
length of approximately 1240 m, desilting the bottom outlet channel to the confluence
with Sohodol River, as well as desilting the surface outlet channel downstream of the
energy dissipator pool);
- repairs to the access bridge from the canopy to the operation tower (Figure 1);
- repairs to the operation tower cabin, with polyyinil and glass joinery and roof
insulation;
- rehabilitation of the hydromechanic equipments;
- electrical installations;
- water management information and warning-alarm system;
- access road restoration.
The investment works began in December 2009 and were received in April 2011.
Figure 1. Longitudinal section of the access bridge
HYDROLOGICAL DATA
The reservoir in question falls in the IInd class of importance and B category of importance.
According to STAS 4068/2-62, Râpa Albastră reservoir was sized using the flow with the probability
of exceedance of 1% and was verified using the flow with the probability of exceedance of 0.1% with
a 20% increase safety.
Simila River has the following features (Ministerul Mediului,1992):
- catchment area in Râpa Albastră sealing section F = 254 kmp;
- average altitude 186 m
- River length from spring to dam L = 8,0 km;
- annual average flow at the upstream hydrometric station Qmm = 0,277 mc/s
Characteristics of flood waves are presented in Table 1.

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Table 1. Characteristics of flood waves
No Characteristics of flood waves
1 1,2x0,1% probability flow – cubic meters per second 534
2 0,1% probability flow - cubic meters per second 445
3 1% probability flow - cubic meters per second 260
4 Total time – hours 85
5 Increase time - hours 20
6 Form factor γ 0,27
7 1,2x0,1% probability volume – million cubic meters 31,14
8 0,1% probability volume – million cubic meters 25,95
9 1% probability volume – million cubic meters 15,16
GEOLOGICAL CHARACTERISTICS OF THE SITE
The site of the Râpa Albastră reservoir is a part of the Moldavian Platform, which is
characterized by uniformity of deposits that compose it. The foundation is made of marl clay horizon,
at a depth of more than 6 m, consisting of marly clays, sometimes with calcareous concretions and
intercalations of clayey sand and clay powders. The foundation is covered, in the basin, by the
recent deposits, Quaternary.
Alluvial deposits in the floodplain, consist of a clayey complex with sand lenses at the top and
a sandy complex with loamy sands, gravel and sometimes rare boulders.
COMPONENT WORKS OF RÂPA ALBASTRĂ RESERVOIR
a) The dam
The dam is a mixed type, made of the sand from quarry materials for the dam body fillings,
combined with bentonite and silty clay side prisms.
The recommendations of the "Geological-Technical Study on Râpa Albastră reservoir, ON
Simila River, Barlad catchment area Design Phase Ist Stage" drafted in April 1972 by the Institute of
Research and Development for Land Reclamation, were that it was necessary to build a sealing
screen to pass through surface permeable layers to the impermeable layer, consisting of marly
clays.
The sealing screen consists of an Else screen made of plain concrete and of a core tight. The
screen was founded in the bedrock at a depth of 1.0 m.The total length of the Else screen is
685.62 m.
For the collection and drainage of seepage through the dam, a drainage system was built. It
consists of:
• a sloping drain in the form of an inverse filter (around the area of the collecting culvert),
behind the tight core
• concrete drainage pipes, with 300 mm interior diameters, laid out along the dam. They
were perforated on the upper pipe generator, in order to collect the infiltrated water from
the body dam. Above them, the filter tipped backwards was put.
• the evacuation culverts are concrete pipes, with 300 mm interior diameters. (Figure 2).
At the intersection of the drainage pipes and the evacuation culverts, concrete manholes were
laced. From the manholes connections were made to the energy dissipator pool of the bottom outlet.

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Figure 2. Cross section of the dam body
b) The surface spillway outlet consists of the following parts:
- access platform to the threshold weir, 10,30 m long;
- frontal threshold weir has no hydro-mechanical equipment. The concrete threshold weir has a
curvilinear profile, type Creager - Ofiterov with a length of 41.00 m front spillway.
- the acceleration zone, 13 m long, where four outer piles are placed, to support the bridge;
- the fast channel, with a 4% slope and a length of 294 m, is made up of:
• a curve connection area with a trapezoidal section, a height of 4.50 m at the left bank
and of 2.55 m at the right bank,
• a trapezoidal cross-section channel, with a height of 2.55 meters, a constant channel
width of 20 m and a length of 237.50 m;
• downstream consolidating constructions
• a connection with the Riverbed downstream: earth channel slope 1: 2, slope 2.1%,
410.50 m long and 20.00 m wide (Figure 3).
Figure 3. Cross section of the weir
c) Medium waters spillway
Râpa Albastră dam is equipped with a medium water spillway that consists of 3 holes closed
with gates 1750x2300 mm / 5,4 m. Medium waters operating regime requires maintaining the gates
normally in open position, unless interventions are perfomed on the hydraulic constructions and
installations of bottom outlet.

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d) Bottom outlet is a rectangular culvert, made up of 3 compartments with the dimensions of
1.75x2,30 m each. The culvert has a total length of 78 m.
Hydro-mechanical equipment for the bottom outlet consists of:
¾ metalic grid: 1750x2450 mm/13,5 m
¾ cofferdam 1100x1500 mm/13,5 m
¾ flat slide gate for draining the lake with dimensions of 1100x1500 mm/ 13,50 m,
operated elecrically, with normal position closed.
e) The water intake is located in the right side of the operation tower. There are two pipes
with different whirlpools levels, for irrigation and industrial water demand.
CHARACTERISTIC LEVELS AND VOLUMES
The land rates reference plan is Black Sea 1975 and they were updated by topographic
measurements (Administraţia Bazinală Prut – Bârlad, 2013), performed by specialized staff from the
Prut-Barlad Water Basinal Administration on the lake basin, dam body and related constructions in
2012 (Table 2).
Table 2. Characteristic levels and volumes
Parameters Characteristic levels maBS
- bottom outlet sill 70,00
- pipe intake level for irrigation water 73,72
- pipe intake level for industrial water 76,22
- medium waters spillway – operation tower 81,32
- surface outlet - threshold weir 83,71
Parameters determined by
structural characteristics
Parameters determined by
the operating conditions
- dam canopy 86,84
- normal retention level-N.R.L. 81,32
- 1% probability of exceedance 84,71
- 0.1% probability of exceedance 85,74
Parameters
Parameters determined by
structural characteristics - 1.2x0.1% probability of exceedance 86,16
Volume mil cm
- global (at dam canopy) 23,159
- 1% probability level 16,438
- at surface outlet - threshold weir 13,625
Parameters determined
by the operating
conditions - at N.R.L. 8,134
- total (0.1%x1,2 probability level) 20,922
- atennuation between 1% prob. level and N.R.L. 8,304
- atennuation between 0.1%x1,2 probability level and N.R.L. 12,788
Parameters determined by
structural characteristics - saftey (between the 1.2x0.1% probability of exceedance
level and dam canopy) 2,237
COMPONENT ELEMENTS OF THE BEHAVIOUR MONITORING SYSTEM FOR RAPA
ALBASTRA RESERVOIR
According to the current legislation (NTLH–021/2002) Râpa Albastră dam has a 0.45 risk
index (established in the Evaluation of Râpa Albastră reservoir safety in exploitation and the
authorization number 530/6.07.2007), that fits the reservoir in „B- special”, category of importance.
Monitoring behaviour is done accordingly to the „Project of special monitoring” (Administraţia
Bazinală Prut – Bârlad, 2007).
Measuring installations for external stresses
• 4 vertical hydrometric stations are used to monitor hydrological parameters for Râpa Albastră
reservoir:
- upstream of the lake, at Băcani hydrometric station for tracking the evolution of the inflow in
the lake;

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- on the upstream dam slope, near the operation tower, for tracking the evolution of the
levels/volumes in the lake;
- in the access channel of the surface outlet, downstream the threshold weir, for tracking
spillway flows;
- at Simila hydrometric station for tracking the evolution of outflow from the lake;
To follow the evolution of hydrological parameters in the reservoir and at the downstream
hydrometric station it is in use a collecting/data transmission system for water management:
- level sensor at the operation tower for real-time transmission of the data to the local dispatch
and other levels of analysis: Vaslui Water Management System and Prut-Bârlad Water Basinal
Administration.
- level sensor at the downstream hydrometric station for real-time transmission of the date data
to the local dispatch and other levels of analysis: Vaslui Water Management System and Prut-Bârlad
Water Basinal Administration.
• 2 rain gauges to measure rainfalls in the catchment of the reservoir (1 located at Băcani
hydrometric station and 1 located near Râpa Albastră dam)
Measuring installations of the dam response to stress
• For tracking the evolution of vertical deformations are used:
- 25 vertical axis landmarks on the dam;
- 3 fixed landmarks (2 in the right slope and 1 in the left slope);
- 2 landmarks on the operation tower (T1, T2) and 1 landmark on the support pillar that was
built in 2012 (P1);
• For tracking the evolution of body dam seepage, 9 piezometric wells are used; (Figure 4).
Figure 4. Dam body plan view with the location of the measuring installations.
RECORDING AND ANALYSIS OF SPECIAL EVENTS IN EZER RESERVOIR BEHAVIOUR
Special events recorded during the execution of the dam
• Due to the pressure of the soil layers, placed above the initial measuring installations that
were inserted in the fillings (hydrostatic cells and closed circuit piezometers), the tubes were

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strangled, making it impossible for water to circulate and be measured. The Varnis tubes were
replaced with plastic tubes which have been shown to be effective in other earth dams.
Because the manholes were not built in due time, on the downstream slope and also because
of the time lag between the construction of the downstream prism and the rest of the body dam,
some plastic tubes were buried or cut and were recovered only partially. In these circumstances it
was considered necessary to amend the Measuring Installations Project, giving up hydrostatic cells
and closed circuit piezometers.
• The significant rainfalls recorded in the summer of 1974 (July) led to the deterioration of the
County Road DJ 245 (which provided access to the reservoir). Desilting works and recovery of
affected areas were required..
• During the constructions the technical solution regarding the access bridge was changed.
Finally it was adopted the technical solution with two pillars for the bridge, instead of a single pillar
Special events recorded during operation
In the winter of 1992 (February), due to strong frost phenomenon, there was found damage
and tilt of the last pillar of the access bridge, causing the failure of a section of the bridge.
Immediate measures were taken:
- Replacing a section of the bridge with a metallic structure (beam) and anchoring the support
pillar;
- Precision geodetic measurements (6 series) for the operation tower and the access bridge to
monitor behaviour in time. The measurement didn’t reveal any atypical behavioral phenomenon.
But still, it was imperative that a permanent technical solution was found. It was later
implemented under the project „Safety re-inforcement of Râpa Albastră reservoir, located on the
Simila River, in Vaslui county”.
ANALYSIS OF THE SAFETY IN OPERATION OF THE RESERVOIR AND RESULTS
External stresses recorded during the years 1997 – 2012
The database with water levels in the reservoir, rainfalls, temperatures, floods recorded
between the years 1997-2012 (Administraţia Bazinală Prut – Bârlad, 2012), provided by the Water
Basinal Adminstration Prut-Barlad, was used for the interpretation of the reservoir behaviour (Table
3).
Table 3. External stresses between the years 1997 and 2012
Water level (maBS) Precipitations (mm)
Maximmum
Year Max
level
Min
level
Average
level
Level
diff.
(m)
Year
Total monthly monthly
1997 81,40 0,67 514,1 116,3 41,2
1998 81,30 80,64 81,05 0,66 468,9 94,8 70,2
1999 82,92 80,92 81,15 2,00 375,8 62,0 88,1
2000 81,26 80,18 80,71 1,08 293,1 68,8 32,5
2001 81,15 80,37 80,71 0,78 316,9 53,6 26,5
2002 81,27 80,39 80,96 0,88 487,6 141,4 38,6
2003 81,41 80,69 81,02 0,72 384,3 84,7 43,5
2004 81,57 80,80 81,10 0,77 489,9 101,2 56,0
2005 81,38 79,84 80,54 1,54 419,4 89,9 39,3
2006 80,75 80,05 80,28 0,70 429,9 107,7 47,7
2007 81,24 80,24 80,73 1,00 550,5 99,0 65,8
2008 81,21 78,10 80,27 3,11 380,7 69,1 25,5
2009 79,38 77,12 78,57 2,26 312,5 54,9 17,6
2010 78,62 74,48 77,12 4,14 544,87 116,5 23,5

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2011 77,46 74,37 77,00 3,09 290,3 58,5 25,8
2012 79,13 77,04 78,10 2,09 286,2 67,4 25,8
We can observe that the maximum water level in the reservoir (82,92 maBS) was inferior to
the surface outlet - threshold weir with 0,79 m, so in the entire existance of the dam, the outflows
were transited only through the medium waters spillway and the bottom outlet.
Visual observations
a) Integrity of the structure, including the foundation and the embankments
The visual observations made by the operation personnel didn’t reveal any structural changes
of the dam’s body and foundation or of the embankments.
b) Reservoir and embankments
No changes in embankments or lake bordeline geometry were reported and no ravines,
landslides or leakings were revealed.
c) Outlets
The outlets of the Râpa Albastră dam have a good tehnical status.
d) Status of the upstream and downstream channels
In the project „Safety re-inforcement of Râpa Albastră reservoir, located on the Simila River,
in Vaslui county” the following works were implemented:
- restoring transport capacity of the bottom outlet channel,
- calibration of Simila River bed over a length of approximately 1240 m,
- desilting the bottom outlet channel to the confluence with Sohodol River,
- desilting the surface outlet channel downstream of the energy dissipator pool
The technical status of the upstream and downstream channels is very good.
e) Acces ways
The access ways to the dam was rehabilitated in the year 2011.
f) Hydromechanical equipments
The hydromechanical equipments have a good operation status.
Evolution of monitored parameters
Analysis of the behaviour in time of the reservoir was done studying the evolution of the
response parameters (hydrostatic level in the piezometric wells, infiltrations, vertical deformations) to
the external stresses. Data interpretation was completed by direct visual observations made during
the entire exitence period of the Râpa Albastra reservoir.
a) Infiltrations
The variation of the hydrostatic levels in the piezometric wells was the first response of dam
body to the external stresses: reservoir water level variations, rainfalls and temperatures. The
seepage regime through dam body and foundation soil was also influenced.
The hydrogeology of the area of the dam location (foundation soil, slopes) required the
construction of a mixed type dam, with a bentonite core, an Else sealing screen from the right slope
along the dam, to the left slope.
The measuring installations used during the construction and also during the exploitation of
the dam provide data on behaviour in time monitoring of the dam, slopes and the foundation soil.
From the study of the hydrostatic levels in the piezometric wells we have concluded that in all
three control sections, the water level variation is very little influenced by the changes in lake level
(possibly because the dam has a bentonite core).
Depression curves made for the three control sections occupy small areas of the dam body,
as the seepage waters are collected by the filter drain and then routed through collection -

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evacuation culverts to the bottom outlet channel. The drainage system of Râpa Albastră dam
consists mainly of the inverse filter inside the dam and the collection - evacuation culverts, that are
monitored in the 2 manholes placed on the left side of the dam.
The measuring point of infiltration water for the left branch is positioned at a lower elevation,
the bottom outlet channel. The measured seepage flows at the evacuation culvert had maximum
values of 0.15 l/s, weakly influenced by periods of precipitation.
The evacuation culvert for the right branch is permanently dry.
b) Compactions
During 11.06.1984 – 10.05.2012, 38 cycles of observation were carried out.
Observations were made on a number of 25 mobile landmarks for compaction, planted on the
dam canopy. In the year 2012 the serie "0" of reference measurements was carried out for a mobile
landmark placed on the access bridge and two landmarks placed on the ceiling of the operation
tower.
By analyzing the temporal evolution chart of the vertical deformations we have observed a
normal evolution of the compaction phenomenon
CONCLUSIONS
The special events recorded during the construction and during the operation of the dam have
imposed the implementation of a systematic behaviour in time monitoring of the hydrotechnic
constructions at Râpa Albastră reservoir.
The behaviour in time monitoring performed by interpreting the visual observations and the
measurement data from gauges, in relation to external stresses on the dam, allows rapid reporting of
exceedances of critical thresholds at monitored elements and of any typical behaviours of the dam.
The behaviour monitoring of Râpa Albastră reservoir is recommended to be continued
accordingly to the "Project of special monitoring".
References
Administraţia Bazinală Prut – Bârlad, (2007) Proiect de urmărire specială a acumulării Râpa Albastră
Administraţia Bazinală Prut – Bârlad, (2012) Raportul de sinteză privind urmărirea comportării construcţiilor la
acumularea Râpa Albastră, perioada de analiză aprilie 2010 – octombrie 2012
Administraţia Bazinală Prut – Bârlad, (2013) Raport anual de sinteză privind activitatea de urmărirea
comportării construcțiilor din patrimoniul Administraţiei Bazinale de Apă Prut – Bârlad în anul 2012
Administraţia Bazinală Prut – Bârlad, (2013) Regulamentul de exploatare al acumulării Râpa Albastră
Ministerul Mediului, (1992), Atlasul cadastrului apelor din România, Editura Romcart S.A., Bucureşti 448,