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This study focuses on developing rule curves for sluice gate operation and water level management in Lake Micro Prespa, an international lake shared by Greece and Albania, critical for biodiversity and water storage. The research outlines the steps followed, including area-volume curve development and impact analysis on Macro Prespa's water level. The study evaluates different gate operations and simulations for effective water level management, highlighting the importance of accurate calculations and ease of use of developed rule curves. The conclusions suggest successful simulations and the need for future improvements in programming these processes for optimal operation.
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Development of rule curves for sluice gate operation and water level management in lake Micro Prespa George Parisopoulos1, Georgios Sapountzakis1, Pantazis Georgiou2, Maria Giamouri1, Myrsini Malakou3 1NAGREF, Institute of Agricultural Machinery and Construction (I.A.M.C.), 2 School of Agriculture, Aristotelio Univ. of Thessaloniki3 Society for the Protection of Prespa, Agios Germanos, Greece Water Observation and Information System for Decision Support Ohrid, Republic of Macedonia, 25-29 May 2010
Lake Micro Prespa An international lake shared by Greece (90%) and Albania (10%). • The area is designated as : • a Ramsar site • an SCI/SPA NATURA 2000 site • Nature Protection zones of the Prespa National Park The lake forms the upper part of a larger hydro-system, including lakes Macro Prespa and Ohrid. Water level is controlled by regulating the spillage to Macro Prespa.
Simplified representation of lake Micro Prespa hydro-system
Lake level The temporal variation, as well as the rate of rising or dropping, decisively influence all characteristic ecosystem functions, in particular biodiversity, biotopes, rare and endemic species of flora and fauna hosted
a. protect bird nests from predators High water level
c. Provide water storage for irrigation but cause poor drainage at the lakeside fields
Control structure : Four sluice gates at Koula Spillage elevation: Unchanged
Plan view Cross sections
Need for an operational guide Development of rule curves Simple and easy to use
Development of rule curves The steps followed : Development of Area – Volume curve of lake Micro Prespa Calculation of outflow discharge Q (depending on gates position and water level) Calculation of disposed volume V for a certain time step dt (V=Q . dt) Calculation of water level drop Using lake’s area - volume curves
Initial inherent assumption The lake is at a steady state (inflows = outflows) Lake level drop comes exclusively from controlled outflows However Rule curves can also be used in periods of water level rising or dropping assuming that the trend (with closed gates) at time step i+1 will be the same with the trend at time step i
Impact on water level of Macro Prespa Water storage between the low level scenario (+850,60m a.s.l.) and the high level scenario (+851,00m a.s.l.) 19.3 hm3 Impact on water level of Macro Prespa < 10 cm
Free overflow (Sluice gates are fully open) (Terzidis, 1997) where: Q (m3/sec): overflow discharge, b (m): width of the canal, Η (m): hydraulic head, C (m1/2/sec): spillage coefficient (Theoretical value C= g1/ 2 * (2/3)3 / 2 =1,705)
Orifice flow (Sluice gates are partially open) (Bos, 1976) where: D(m): the opening of the sluice gate measured from the bottom, Cd: coefficient equal to 0,60 when 1,5 < (Η/D) < 3,5 or 0,605 when 3,5 < (Η/D) < 5,0 or 0,61 when 5,0 < (Η/D), CV: coefficient with values close to 1, as the velocity at the spot of level measurement is very small, CC: coefficient taking values between 0,63 και 0,62. Used values in this paper : Cd= 0,60 and CC=0,625
Rule curves of the 1st gate Impact of different operations on the lake level
Rule curves of each individual gate, and five combinations for free overflow
Testing of rule curves • Rule curves were used in two simulation runs concerning water level management during spring of 2005 and 2006 • The recorded time series of the water level were transformed to water level time series that would have been recorded, if all gates were closed • Sluice gates operation: Fully open or close • Simulation of the sluice gates operation by 3 different operators for each year Level target : + 850,57 m Duration : The whole simulation period
Procedure Every operator was provided with: The developed rule curves The simulated water level at the time of operation The previous gate operations The operation decided at time step i, resulted into a simulated water level at time step i+1. The simulated water level was calculated after considering both the operation at time step i and the transformed water level data records. Note: The operators Had no previous experience Received very short training (e.g. 1 hr)
Test 1. Simulated lake level during spring 2005, using the developed rule curves
Test 2. Simulated lake level during spring 2006, using the developed rule curves
Conclusions • All simulations were successful as the water level remained close to the target level. • The developed rule curves allow a quick and reliable estimation of the impact of gates operation on the lake level. • The accuracy of the diagrams is related to the accuracy of outflows calculations and the lake’s area - volume function. • Their use requires neither specific knowledge nor particular training.
Future improvements Programming of all the above processes and procedures, so that the optimal operation could be automatically selected.
