© Acta hydrotechnica 21/35 (2003), Ljubljana
ISSN 1581-0267
77
UDK/UDC: 532.57:574.5:627.8 Prejeto/Received: 12. 10. 2003
Strokovni prispevek – Professional paper Sprejeto/Accepted: 25. 6. 2004
EKOHIDROLOŠKI PROCESI NA ZAJEMNEM OBJEKTU ZA
HIDROELEKTRARNO PLA VE, SLOVENIJA
ECOHYDROLOGICAL PROCESSES ON THE INTAKE STRUCTURE OF
THE PLA VE HYDROPOWER PLANT, SLOVENIA
Mitja BRILLY
Luka ŠTRAVS
Gregor PETKOVŠEK
Mihael J. TOMAN
Zajem za HE Plave je sestavljen iz 6800 m dolge galerije, s padcem 0,315 ‰ in s premerom 7,80 m.
Mirni tok s prosto gladino v kanalu nadzoruje zapornica. V zadnjih desetih letih je proizvodnja
mo či v letnem času upadla do 10 %. Najprej je bila izvedena preiskava tehniške službe HE, vendar
ta ni pokazala pravih vzrokov upada mo či. Konec avgusta 2001 so se za čele izvajati meritve hitrosti
na dovodnem kanalu. Merilec hitrosti z zapisovalcem podatkov je tri dni meril hitrosti. Nadaljnje tri
mesece smo merili hitrosti z ultrazvo čnim merilcem hitrosti, in sicer do konca novembra. Pri
demontaži merilca so bili na instrumentu ugotovljeni trdi izrastki organskega izvora. Vzorec z
opreme in trije vzorci za biološko analizo, ki so bili postrgani z obloge kanala, so bili pregledani na
Oddelku za biologijo Univerze v Ljubljani. Ugotovljena je bila velika številčnost li čink iz družine
Simulidae, ki so prekrivale merilec. Vzorci, postrgani z oblog kanala, so vsebovali perifitonsko
združbo relativno majhne raznolikosti. Prevladovale so kremenaste in zelene alge. Z letnimi časi se
je spreminjala tudi hrapavost galerije, ki smo jo spremljali tri leta na osnovi proizvodnje HE. Kote
vode na dovodnem kanalu in ob iztoku so bile korelirane za stabilne pogoje. S hidravli čnim
modeliranjem smo analizirali tudi spremembe v hrapavosti.
Klju čne besede: hidroelektrarna, meritve hitrosti vode, hrapavost, li činka Simulidae.
The intake structure of the Plave power plant has a 6800 m long tunnel, with a longitudinal slope of
0.315 ‰ and a diameter of 7.80 m. In the tunnel the subcritical free surface flow is controlled by a
sluice gate. In summer, the power production has decreased in the past few years up to 10 percent.
An in-house investigation was carried out, however failing to show the underlying causes of the
power decrease. At the end of August 2001, velocity measurements were launched on the intake
structure. For three days, the current meter with an internal memory measured the velocity. After
that velocities were measured with ultrasonic current meter for three months, until the end of
November 2001. When dismantling the current meter it was discovered that the instrument was
covered with unidentified organisms. The sample of biogenesis from the current meter and three
samples for biological analysis scraped off of the wall of the tunnel were investigated in the
laboratory of the Biological Department of the University of Ljubljana. It was established that the
current meter was completely covered with dipteran larvae (f. Simulidae). The three scraped
samples were identified as periphyton community with relatively low diversity. Cyanobacteria and
diatoms prevailed. The roughness of the tunnel changed seasonally, which was analyzed from the
monitoring data of power plant production for a three-year period. Water levels on the intake and
outlet and discharge were correlated for steady state conditions. Changes in roughness were also
analyzed with hydraulic modelling.
Key words: hydropower plant, velocity measurements of water, roughness, larvae Simulidae

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
78
1. UVOD
Hidroelektrarna Plave, ki je bila leta 1939
zgrajena na reki So či, ima 2 turbini z mo čjo
8 MW in 74 m
3
/s pretoka. Rezervoar na dotoku
vode v tla čne cevovode HE je s pregrado Ajba
povezan s kratkim vstopnim odprtim kanalom
in 6800 m dolgo galerijo, ki ima padec
0,315 ‰ in konstantni pre čni prerez (slika 1).
Skozi galerijo te če voda v toku s prosto
gladino. Kota vode pri dotoku na turbine je
konstantna in znaša 101,30 m ker je
vzdrževana s koto preliva tako, da so tla čne
cevi z gornje strani pod konstantnim tlakom.
Pretok v galeriji uravnava zapornica na
pregradi. Informacijski center hidroelektrarne
je daljinsko povezan z vodomerom na
dovodnem delu. Upravljanje obratovanja
hidroelektrarne je avtomatsko, tako da se
optimizira glede na gladino vode na vhodu v
kanal. Optimalna proizvodnja energije z enim
agregatom dosega 8 MW mo či, pretok 36 m
3
/s
in 2,2 m proste gladine v galeriji. Pri
obratovanju obeh agregatov je optimalna mo č
16 MW, pretok 74 m
3
/s, prosta gladina vode v
galeriji pa 0,75 m pod stropom.
Že leta 1999 je bilo ugotovljeno, da HE z
enim agregatom ne dosega maksimalne želene
proizvodnje mo či. Ob obratovanju enega
agregata naj bi bila kota vode pri dotoku na
turbine konstanta in naj bi znašala 102,15 m.
Junija 1999 je v času nizkega poletnega
pretoka upravljalec pove čal koto vode pri
dotoku na turbine, da bi ohranil maksimalno
proizvodnjo agregata, slika 2. Kota vode je v
desetih dneh po časi narasla na 102,38 m. Do
tega je prišlo že nekajkrat prej, vendar proces
pred letom 1999 nikoli ni bil tako zna čilen. V
obratovanju HE se je vodna kota pri dotoku na
turbine ob časno sicer zvišala in tako za
agregate priskrbela enako koli čino vode. To je
bilo možno zato, ker HE (z eno turbino) ne
obratuje ob maksimalnem pretoku. Pri
obratovanju z obema turbinama to ni možno,
saj je obratovanje ob maksimalnem pretoku z
obema turbinama programsko omejeno in
regulirano z visokovodnim prelivom.
1. INTRODUCTION
The Hydropower Plant Plave built on the
So ča River in 1939 has two turbines of 8 MW
power each and discharge of 74 m
3
/s. The
surge tank on the intake of the penstock
supplying the turbines of the hydroelectric
power plant is connected to the Ajba dam with
a short open channel and 6800 meter long
tunnel, which has a longitudinal slope of
0.315 ‰ and a constant cross-section (Figure
1). The water flows through the tunnel as a
free-surface flow. The water level at the surge
tank is constantly kept at 101.30 m with an
overflow spillway; the penstock is under
constant pressure on topside.
The discharge in the tunnel is controlled by
a sluice gate on the dam. On the inflow
channel, the water level gauge is connected
online with the information centre of the
power plant. The power plant is under
automatic control which is optimized on water
level in the inflow channel. The optimal
production of energy with one turbine is 8
MW with a discharge of 36 m
3
/s, and with a
2.20 m of free board in the tunnel. When both
turbines operate, the optimal power is 16 MW,
discharge 74 m
3
/s, board in the tunnel 0.75 m.
In summer 1999, the power plant failed to
reach its maximum production with one
turbine. With one turbine in operation, the
water level on the intake structure should be
constant i.e. 102.15 m. In June 1999, the
operator increased the water level on the
intake structure to maintain the maximum
production of the plant during the summer low
flow season (Figure 2). The water level slowly
increased to 102.38 m in ten days. The
phenomena had occurred several times before,
but the process was never as significant as in
1999. From time to time, the operator on the
power plant increased the water level in the
inflow channel to provide the same amount of
water. This was possible because (with only
one turbine) the power plant operates below
the maximum discharge. However, this is not
possible during maximum discharge operation
with both turbines, because the water level in
the inflow channel is controlled by the
overflow spillway.

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
79
Slika 1. Pre čni prerez dovodnega tunela HE Plave –
kopija originalne dokumentacije v italijanskem jeziku.
Figure 1. Cross sections of the Plave hydropower plant tunnel –
copy from the original documentation in Italian.
Slika 2. Proizvodnja energije v juniju leta 1999.
Figure 2. Power production data in June1999.

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
80
Galerijo so odklopili, vodo izpustili in
temeljito pregledali objekt. Tehni čna analiza
HE ni nakazala možnega vzroka,
nekontrolirana izguba vode zaradi razpok ali
fizi čnih poškodb galerije v objektu HE pa je
bila izklju čena.
Poleti 2001 je pojav raziskala Univerza v
Ljubljani. Na vhodu v tunel sta bila
postavljena dva merilca preto čnih hitrosti
(slika 3): mehani čni merilec hitrosti z
zapisovalcem podatkov in Dopplerjev merilec
hitrosti. Meritve so se za čele avgusta in
zaklju čile oktobra 2001 (slika 4). Pri
demontaži merilca Valeport je bil merilec
prekrit s trdimi izrastki. Konec oktobra so bili
z oblog kanala in galerije odvzeti še vzorci za
biološko analizo.
The tunnel was switched off, the water
evacuated and the structure carefully
inspected. Technical analyses of the power
plant functioning failed to reveal the origin of
the problem, while uncontrolled water loss due
to tunnel cracks or other physical damage on
the power plant construction was excluded as
the underlying cause.
In summer 2001, the phenomena were
investigated by the University of Ljubljana.
Two current meters were put into the intake
channel (Figure 3): a mechanical current meter
with a memory unit and a Doppler velocity
meter. The measurements and observations
started in August and were finished in October
2001 (Figure 4). Upon dismantling of the
equipment the current meters were completely
covered with small features. In October 2001
we started with biological sampling in the
tunnel.
Slika 3. Pregrada Ajba in dotok v galerijo HE Plave.

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
81
Figure 3. Ajba Dam with intake structure of tunnel HE Plave.
Slika 4. Meritve hitrosti, gladine in temperature vode na vtoku v galerijo
Figure 4. Measurements of velocity, level and temperature of water in intake structure of the tunnel
Fenomen zmanjševanja obratovalne mo či je
bil analiziran na osnovi obratovalnih podatkov
HE Plave iz let 1999, 2000 in 2001.
Analizirani so bili predvsem podatki o
proizvodnji mo či, agregatnih pretokih in
gladini vode na vstopu v galerijo, cevovod pod
tlakom in iztok HE.
2. ANALIZA PODATKOV O
OBRATOVANJU HE
Podatki o proizvodnji mo či in obratovanju
sistema HE, ki so bili zbrani na terenu, so bili
shranjeni v podatkovno banko. Podatki so bili
zbrani za zelo kratke, vendar razli čno dolge
nekaj sekundne časovne intervale. Pred analizo
je bilo treba obsežno množico izmerjenih
podatkov urediti. Podatke smo izbrali tako, da
smo se izognili nihanju, ki ga povzro čajo
nestabilni operativni pogoji sistema zaradi
sprememb v proizvodnji mo či ali vpliv visokih
voda reke So če na izlivu iz turbine. Iz
arhivirane podatkovne bazi so bili zbrani in
obdelani predvsem podatki v stabilnem in
stalnem stanju na nekaj ur. Zbrani so bili
naslednji podatki: pretok na agregatih,
proizvodnja mo či na sistemu, kota vode na
vstopu v galerijo in kote vode v vodostanu.
Podatki so bili obdelani in predstavljeni kot
The phenomenon of decreasing power
production was analyzed on the basis of the
operational data of the Plave hydropower plant
in years 1999, 2000, and 2001. Data on power
production, turbine discharges and water levels
in the inflow channel, surge tank and the outlet
of the plant were analyzed.
2. ANALYSIS OF THE POWER
PLANT OPERATIONAL DATA
Online collected field data of power
production and operation of the hydropower
plant system were stored in a data bank. Data
were collected with very short, though
differently-sized time steps of several seconds.
There was a large amount of the measured data
that needed to be arranged before an analysis.
The data were chosen in a way as to avoid the
oscillation produced by unstable operational
conditions of the system, caused by changes in
power production or impacts of the high water
level of the So ča river on the outlet from the
turbine. Data of stable, steady state of several
hours were collected and processed from the
archive database. The following data were
collected: discharge on turbines, power
production of the system, water levels in the
inflow channel, and water levels in the surge
tank. Data were processed and extracted from

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
82
srednje urne vrednosti.
Najprej so bili analizirani podatki iz
opazovalnega obdobja med avgustom in
oktobrom 2001. Nizki pretok reke So če je bil
vzrok nizki proizvodnji mo či na enem od
agregatov od konca avgusta do sredine
septembra. Visok pretok od sredine septembra
do sredine oktobra je omogo čal optimalno
proizvodnjo mo či na obeh agregatih. V
razmerju med pretokom in koto vode na
dovodnem kanalu ni bilo izrazitih razlik.
Nadalje smo analizirali arhivirane podatke od
za četka leta 1999 do obdobja terenskih
opazovanj iz leta 2001. Podatki so bili
obdelani na podoben na čin kot v prvi stopnji
analize. Diagram, ki prikazuje razmerja med
mo čjo in kotami vode na dovodnem kanalu, je
prikazan na sliki 5. Prikazane so izrazite
spremembe v kotah vode na dovodnem kanalu.
Opazovalno obdobje med avgustom in
oktobrom je minilo brez bistvenega upada
prevodnosti galerije.
Hidravli čni izra čuni pretoka v kanalu so
temeljili na Manningovi ena čbi (Brater in ost.,
1996). Rezultati izra čunov so prikazani v
preglednici 1. Koeficient hrapavosti se izrazito
spreminja. Manningov koeficient hrapavosti je
bil prera čunan na absolutno višino hrap. Ta
sega od 0,012 mm v dobrih pogojih do 4,4 mm
v najslabših pogojih v kanalu.
the archive as mean hourly values.
Data for the observation period from
August to October 2001 were analysed first.
Low flows in the So ča River resulted in low
power production of one of the turbines from
the end of August to mid-September. From
mid-September to mid-October, high flows
enabled optimal power production on both
turbines. There were no significant differences
in relations between discharge and water levels
in the inflow channel.
In the next stage we analysed the archived
data from the beginning of 1999 to the period
of field observations in 2001. Data were
processed in the same way as in the first stage
of the analysis. A diagram with relations
between power and the water levels in the
inflow channel is shown on Figure 5. There
are significant changes of water levels in the
inflow channel. Observation period from
August to October was without a significant
decrease in the conductivity of the tunnel.
The hydraulic calculation of the flow in the
tunnel was based on the Manning equation
(Brater at al., 1996). Results of these
calculations are shown in Table 1. The
coefficient of roughness varies significantly.
The Manning roughness coefficient was
recalculated to the absolute roughness height.
The roughness height varies from 0.012 mm in
good conditions of the tunnel to 4.4 mm in the
worst conditions.
101,00
101,50
102,00
102,50
103,00
103,50
104,00
104,50
0,00 5,00 10,00 15,00 20,00
power in MW
altitude of water level in m
1999
2000
2001
Slika 5. Razmerje: mo č–kota vode.
Figure 5. Relation power–water level.

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
83
Preglednica 1. Rezultati hidravli čnih izra čunov.
Table 1. Results of hydraulic calculations.
datum – Date pretok v m
3
/s –
Discharge in m
3
/s
koeficient hrapavosti –
Roughness coefficient
hrapavost v mm –
Roughness in mm
07-06-1999 36,5 0,012 0,087172
04-08-1999 36,8 0,0165 4,388972
07-11-1999 71,4 0,0129 0,335985
10-05-2000 64,7 0,0143 1,109794
28-06-2000 35,8 0,0138 0,729321
27-10-2000 36,1 0,0118 0,052941
28-05-2001 74,8 0,0123 0,1721
12-08-2001 35,4 0,0115 0,012501
3. ANALIZA BIOLOŠKIH
VZORCEV
Vzorci z merilne opreme in oblog kanala so
bili odvzeti v oktobru in poslani Skupini za
limnologijo Oddelka za biologijo Univerze v
Ljubljani. Mikroskopski pregled je potrdil
prisotnost ve čjega števila li čink iz družine
Simulidae (slika 5, Moss, 1988; Barnes in ost.
1995; Ruppert in Barnes 2001).
Vzorci, postrgani s kovinskih delov merilne
opreme, so vsebovali za teko če vode tipi čno
perifitonsko združbo. Najbolj pogoste so bile
kremenaste in zelene alge ter posamezne
praživali (Protozoa). Zanimivo je, da je
kovinski substrat pokrivalo veliko število
li čink mušice dvokrilcev iz družine Simulidae.
Te majhne, manj kot 1 cm velike li činke, so
pomemben sestavni del makrozoobentoških
združb in so pritrjene na kamnih v vodah s
hitrim tokom. Prehranjujejo se z delci, ki jih
vodni tok plavi s seboj, li činka pa izkoristi
organski detritus.
Koncentracija organskih snovi je eden
izmed omejujo čih dejavnikov rasti populacije
li čink v rekah. V primeru reke So če je koli čina
suspendiranih snovi v vodnem stolpu zadostna
za razvoj obilne populacije Simulidae. Vir
suspendiranih snovi je fitoplankton, v
zajezitvah na So či pa tudi odtrgani perifiton, ki
ga reka plavi. Dinamika populacije je zna čilna
za slovenske klimatske pogoje, njena
števil čnost pa je najve čja poleti.
3. ANALYSIS OF BIOLOGICAL
SAMPLES
Samples from the hydraulics equipment and
the walls of the tunnel were taken in October
and sent to the Group of Limnology of the
Department of Biology, University of
Ljubljana. The microscopic examination
confirmed a high number of dipteran larvae
Simulidae (Figure 5, Moss, 1988; Barnes et
al., 1995; Ruppert & Barnes 2001).
Samples scraped off from the metal parts of
hydraulics equipment contained a periphyton
community, typical for running waters. Most
abundant were diatoms and green algae as well
as protozoan taxa. Surprisingly, numerous
dipteran larvae from the Simulidae family
covered the metal substrate.
Small, 1 cm large larvae are important part
of the macrozoobenthic community in
turbulent running waters and are commonly
fixed on stones. The suspension feeding
animals feed on organic detritus.
Organic matter concentration is one of the
restrictive factors of larvae growth in rivers. In
the case of the So ča River, the amount of
suspended solids in water column is sufficient
for development of an abundant Simulidae
biomass. The source of suspended solids is the
phytoplankton community in reservoirs on the
So ča River as well as the drifting periphyton
assemblages. Population dynamics is
characteristical for Slovenian climate
conditions. Simulidae larvae are most
abundant in summer.

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
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Slika 5. Razvojni krog dvokrilca družine Simulidae in glava li činke s filtrirno napravo.
Figure 5. Development cycle of diptera Simulidae and the head of larvae with filtration device.
4. RAZPRAVA
IN ZAKLJU ČKI
Vzrok za spremembe hidravli čne
prevodnosti kanala, ki je bil raziskan v okviru
terenske raziskave, je treba iskati v vplivu
biotskih dejavnikov na sistem. Ekološko stanje
sistema HE Plave je odvisno od na čina
obratovanja in zunanjih vremenskih pogojev
(temperature zraka, vlažnosti ipd.). Zunanjih
dejavnikov sicer ne moremo spreminjati, lahko
pa vplivamo na notranje dejavnike in
zmanjšamo vpliv omenjenega pojava.
Najboljše razmere za pospešeni razvoj
pojava so ravno v poletnem času, ko HE
obratuje le s polovico kapacitete kanala.
Zaradi manjšega pretoka vode je bilo v tunelu
ve č zra čnega prostora, preto čna hitrost vode je
bila nižja, to pa so bile ugodne razmere za
razvoj li čink.
4. DISCUSION AND
CONCLUSIONS
Variations in hydraulic conductivity of the
tunnel found in the field study were caused by
the influence of biotic factors on the system.
Ecological conditions in the Plave hydropower
system depend on the operation scheme and
outside weather conditions (air temperature,
humidity etc.), and hydrological conditions
(water discharge and water quality). It may not
be possible to change the outside factor, but
we could adapt the inside factors to decrease
the influence of the phenomenon.
The best conditions for persistent blooming
are present during summer months when the
hydropower plant operates only with half of
the tunnel capacity. Due to smaller water
discharge, there was an abundance of airspace
in the tunnel, and water velocity was lower, all
of which stimulated the development of larvae.
VIRI – REFERENCES
Barnes, R. S. K., Mann, K. H., 1995. Fundamentals of Aquatic Ecology. Blackwell Science,
London, 270.
Brater, E. F. et al., 1996. Handbook of Hydraulics: For the Solution of Hydraulic Engineering
Problems. McGraw-Hill, New York.
Moss, B., 1988. Ecology of Fresh Waters. Man and medium. Blackwell Scient. Publ., London, 417.
Ruppert, E. E., Barnes R. D., 2001. Invertebrate Zoology. Saunders College Publishing.
Philadelphia, 1054.

Brilly, M. et al.: Ekohidrološki procesi na zajemnem objektu za hidroelektrarno Plave, Slovenija – Ecohydrological
Processes in the Intake Structure of the Plave Hydropower Plant, Slovenia
© Acta hydrotechnica 21/35 (2003), 77–85, Ljubljana
85
Naslov avtorjev - Authors’ Addresses
prof. dr. Mitja Brilly
Univerza v Ljubljani – University of Ljubljana
Fakulteta za gradbeništvo in geodezijo – Faculty of Civil and Geodetic Engineering
Jamova 2, SI-1000 Ljubljana, Slovenia
E-mail: mbrilly@fgg.uni-lj.si
Luka Štravs
Ministrstvo za okolje, prostor in energijo – Ministry of the Environment, Spatial Planning and
Energy
Urad za prostorski razvoj – Office for Spatial Development
Dunajska 21, SI-1000 Ljubljana, Slovenia
E-mail: luka.stravs@gov.si
 dr. Gregor Petkovšek
Univerza v Ljubljani – University of Ljubljana
Fakulteta za gradbeništvo in geodezijo – Faculty of Civil and Geodetic Engineering
Jamova 2, SI-1000 Ljubljana, Slovenia
E-mail: gpetkovs@cgs.si
prof. dr. Mihael J. Toman
Univerza v Ljubljani – University of Ljubljana
Biotehniška fakulteta – Biotechnical faculty
Oddelek za biologijo – Departement of Biology
Ve čna pot 111, SI-1000 Ljubljana, Slovenia
E-mail: mtoman@bf.uni-lj.si