**3. Climate change**

### **3.1 Precipitation and discharges**

Since mid-1980's precipitation decline in the Kinneret Drainage Basin was documented (**Figures 2**–**6**). During 2013/14 and 2015/16 seasons rainfall was 47% and 68% respectively below the multiannual mean. Major contributors to the Jordan discharge are Dan and Banias rivers. The discharge of Dan and Banias during 2014 (2.67 and 0.16 m3 /s respectively) were the lowest since recent 22 years in comparison with the maximum discharges of 12.8 and 7.4 m3 /s respectively [8, 9]. The annual discharges of those rivers declined by 63 and 14 mcm/y respectively. As a result, annual availability of lake water (inflow minus evaporation) during 1985–2016 indicates a decline from 470 to 225 mcm/y. As the result of promoted trend of dryness, the hydrological dynamics of the Lake Kinneret ecosystem was modified. The Input reduction accompanied by water level decline and elimination of pumping together with close Dam policy eliminated exchange level and prolongation of RT from 5 to 7 to a range of 15–>20 years. Evaluation of SPI (Standard Precipitation Index) values from 87 years precipitation record has indicated 11 and 17 negative indexes (aridity level) during1927–1970 and 1970–2014 respectively, which is an indication of climate change toward dryness. River discharge reduction initiated also changes of the phytoplankton community structure in Lake Kinneret. The Nitrogen supply was diminished resulted Peridinium decline which was replaced by Cyanobacteria dominance.

### **3.2 Rain and headwater discharges**

Decline of rainfall and Jordan River discharges during the last 40 years and historical deficiency of aquifers storage in the Israeli Northern Basin for 100 years were documented by the Israel Hydrological Service [1, 5, 8, 9]. During 2013/14 and 2015/16 rainfall was 47 and 68% respectively below the multiannual average. The Rivers Dan and Banias discharge during 2014 (2.67 and 0.16 m3 /s respectively) were the lowest since recent 22 years. Major contributors to the Jordan flow are Dan and Banias rivers. The annual discharges in those rivers declined by 63 and 14 mcm/y, respectively. A decline from 470 to 225 mcm/y of availability of Kinneret waters (mcm/y) was indicated during 1985–2016.

### **3.3 Air temperature**

The records of daily Maximum and Minimum of air temperatures measured at the Meteorological Station Dafna (northern part of the Hula Valley) indicates an increase since mid-1980s. The air temperature record indicates [13, 14, 17, 19] an annual maximum and minimum elevation by 2.7 and 1.5°C, respectively. Studies on regional water balances confirmed enhancement of water loss not only as

**127**

**Figure 3.**

**Figure 2.**

*Sustainable Utilization of the Lake Kinneret and Its Watershed Ecosystems: A Review*

precipitation and runoffs but also in the underground preferential cavities in the peat soil. Dryness processes of the Hula Valley soil confirm the potential loss of water during dryness periods. Therefore, it was recommended to prevent decline level of soil moisture by suitable irrigation method. Recommended Optimal management is, therefore, moisture enhancement especially during summer time. Climate change and consequent dryness constrains initiated a special legislation, the Peat Soil Convention, which ensured summer water supply for irrigation.

*Fractional polynomial regression between annual (1940–2018) precipitation and years.*

*Groups of decade (10 years) averages of monthly means of water level in Lake Kinneret. Trend of changes,* 

*DOI: http://dx.doi.org/10.5772/intechopen.93727*

*periodical means, and anthropogenic events are indicated.*

*Sustainable Utilization of the Lake Kinneret and Its Watershed Ecosystems: A Review DOI: http://dx.doi.org/10.5772/intechopen.93727*

### **Figure 2.**

*Landscape Architecture - Processes and Practices Towards Sustainable Development*

efficiency aimed at sustainability maintenance.

with the maximum discharges of 12.8 and 7.4 m3

**3. Climate change**

(2.67 and 0.16 m3

dominance.

**3.2 Rain and headwater discharges**

(mcm/y) was indicated during 1985–2016.

**3.3 Air temperature**

**3.1 Precipitation and discharges**

driven by climate change during the recent 15 years field crops area in the watershed was restricted by 35% and Fishponds by 43%. Although agricultural land-use in the Watershed was reduced as well as water availability (from 110 mcm/y to 68 mcm/y) crops and revenue per areal unit were improved simultaneously. This was resulted by technological improvements and land beneficial significance. In other words, natural constrains of water scarcity were achieved by water and land utilization

Since mid-1980's precipitation decline in the Kinneret Drainage Basin was documented (**Figures 2**–**6**). During 2013/14 and 2015/16 seasons rainfall was 47% and 68% respectively below the multiannual mean. Major contributors to the Jordan discharge are Dan and Banias rivers. The discharge of Dan and Banias during 2014

discharges of those rivers declined by 63 and 14 mcm/y respectively. As a result, annual availability of lake water (inflow minus evaporation) during 1985–2016 indicates a decline from 470 to 225 mcm/y. As the result of promoted trend of dryness, the hydrological dynamics of the Lake Kinneret ecosystem was modified. The Input reduction accompanied by water level decline and elimination of pumping together with close Dam policy eliminated exchange level and prolongation of RT from 5 to 7 to a range of 15–>20 years. Evaluation of SPI (Standard Precipitation Index) values from 87 years precipitation record has indicated 11 and 17 negative indexes (aridity level) during1927–1970 and 1970–2014 respectively, which is an indication of climate change toward dryness. River discharge reduction initiated also changes of the phytoplankton community structure in Lake Kinneret. The Nitrogen supply was diminished resulted Peridinium decline which was replaced by Cyanobacteria

Decline of rainfall and Jordan River discharges during the last 40 years and historical deficiency of aquifers storage in the Israeli Northern Basin for 100 years were documented by the Israel Hydrological Service [1, 5, 8, 9]. During 2013/14 and 2015/16 rainfall was 47 and 68% respectively below the multiannual average. The

the lowest since recent 22 years. Major contributors to the Jordan flow are Dan and Banias rivers. The annual discharges in those rivers declined by 63 and 14 mcm/y, respectively. A decline from 470 to 225 mcm/y of availability of Kinneret waters

The records of daily Maximum and Minimum of air temperatures measured at the Meteorological Station Dafna (northern part of the Hula Valley) indicates an increase since mid-1980s. The air temperature record indicates [13, 14, 17, 19] an annual maximum and minimum elevation by 2.7 and 1.5°C, respectively. Studies on regional water balances confirmed enhancement of water loss not only as

Rivers Dan and Banias discharge during 2014 (2.67 and 0.16 m3

/s respectively) were the lowest since recent 22 years in comparison

/s respectively [8, 9]. The annual

/s respectively) were

**126**

*Groups of decade (10 years) averages of monthly means of water level in Lake Kinneret. Trend of changes, periodical means, and anthropogenic events are indicated.*

### **Figure 3.** *Fractional polynomial regression between annual (1940–2018) precipitation and years.*

precipitation and runoffs but also in the underground preferential cavities in the peat soil. Dryness processes of the Hula Valley soil confirm the potential loss of water during dryness periods. Therefore, it was recommended to prevent decline level of soil moisture by suitable irrigation method. Recommended Optimal management is, therefore, moisture enhancement especially during summer time. Climate change and consequent dryness constrains initiated a special legislation, the Peat Soil Convention, which ensured summer water supply for irrigation.

**Figure 4.**

*Fractional polynomial regression between annual Jordan discharge (mcm/y) (left panel) and rainfall (mm/y) (Dafna Station, right panel) during 1969–2018.*

### **Figure 5.**

*Fractional polynomial regressions between rainfall (left panel, Dafna Station), and annual means of WL (mbsl) (right panel), and years.*

**Figure 6.**

*Fractional polynomial regressions between annual means of daily maximum (left panel) and minimum (right panel) air temperature measured in Dafna Station and years during 1940-2020.*

### **4. Lake Kinneret ecosystem**

### **4.1 Water level fluctuations in Lake Kinneret**

The obvious direct relation between Kinneret WL and precipitation regime in the watershed was documented widely in previous studies. Historical (9000 years before present) data of the Kinneret WL was investigated by two different methods [20, 21] and indicated an amplitude of 20 m (197–217 mbsl) WL fluctuations.

**129**

**Figure 7.**

*Sustainable Utilization of the Lake Kinneret and Its Watershed Ecosystems: A Review*

occurred mostly during recent 18 years (**Table 4**) [1, 3, 10, 16, 18–23] .

agricultural water allocation by the National Water Authority.

Monthly means of daily WL measurements has indicated that during 48 years only 97 months (17%) WL was lower than the legislated bottom line of 213 mbsl

Results in **Table 4** and **Figure 2** indicate that during most of the time (83%) the Kinneret WL was not lower than 213 mbsl and, before 2000th, WL was higher than the minimal legislated altitude. The decline of WL below the instructed WL bottom- line (213 mbsl) was recorded during years of exceptional decline of rainfall: 2000–2002, 2008–2011, and 2016–2018, which consequently resulted in significant restriction of

The discussion about dependence relations between phytoplankton and nutrients presented here emphasize the paradigm of an everlasting dilemma: Between phytoplankton composition and nutrient concentrations, who is the boss?

(**Figures 7** and **8**) Algal community structure responds to the concentration of the nutrients or the contrary: does the nutrient concentrations is primary or secondary result of the algal density [6, 11, 23–33]? Nitrogen input is defined as predictor of algal domination in Lake Kinneret: Peridinium or Cyanobacteria. A decline of epilimnetic TN standing stock was documented during 1969 to 2001 accompanied by decline of Peridinium biomass while the biomass of Cyanobacteria increased. TN decline initiated Nitrogen deficiency, which is favored by Cyanobacteria [32] due to their ability of maintain the fixation of atmospheric Nitrogen by the enzyme of Nitrogenase. Earlier studies suggested two elements as key factors for the Peridinium bloom formation: Copper (Cu) and Selenium (Se) [6, 23, 29–33]. The study of the Cu impact was not thoroughly developed but that of Se did it thoroughly. It was confirmed that Se is a limiting factor of Peridinium growth. Before Hula drainage, the chemical conditions of the peat soil were mostly reductive but presently more oxidative and, therefore, limitation of Se is not impossible. Earlier Studies [29, 30], suggested that precipitation and runoff discharges are an important source of bioavailable Se (Selenites and Organic Se) and high availability of Se in surface waters of Kinneret watershed might be a significant supporter of the Peridinium heavy blooms. Therefore, it is suggested that in addition to Nitrogen deficiency, Se input decline affected the decline of Peridinium biomass. Conclusively, the replacement of Peridinium by Cyanobacteria is mostly due to change of nutrients dynamic resulted by climate change. The depletion of Nitrogen supply is based on a long-term record and the recorded data about Se

*Fractional polynomial regressions between annual averages of Epilimnetic loads (ton) of Total nitrogen (TN)* 

*(left), Total phosphorus (TP) (right) inputs through Jordan inflow and years.*

*DOI: http://dx.doi.org/10.5772/intechopen.93727*

**4.2 Nutrient dynamics**

dynamics is partial.

*Sustainable Utilization of the Lake Kinneret and Its Watershed Ecosystems: A Review DOI: http://dx.doi.org/10.5772/intechopen.93727*

Monthly means of daily WL measurements has indicated that during 48 years only 97 months (17%) WL was lower than the legislated bottom line of 213 mbsl occurred mostly during recent 18 years (**Table 4**) [1, 3, 10, 16, 18–23] .

Results in **Table 4** and **Figure 2** indicate that during most of the time (83%) the Kinneret WL was not lower than 213 mbsl and, before 2000th, WL was higher than the minimal legislated altitude. The decline of WL below the instructed WL bottom- line (213 mbsl) was recorded during years of exceptional decline of rainfall: 2000–2002, 2008–2011, and 2016–2018, which consequently resulted in significant restriction of agricultural water allocation by the National Water Authority.

### **4.2 Nutrient dynamics**

*Landscape Architecture - Processes and Practices Towards Sustainable Development*

*Fractional polynomial regression between annual Jordan discharge (mcm/y) (left panel) and rainfall (mm/y)* 

*Fractional polynomial regressions between rainfall (left panel, Dafna Station), and annual means of WL* 

**128**

**Figure 6.**

**Figure 4.**

**Figure 5.**

*(mbsl) (right panel), and years.*

*(Dafna Station, right panel) during 1969–2018.*

**4. Lake Kinneret ecosystem**

**4.1 Water level fluctuations in Lake Kinneret**

*panel) air temperature measured in Dafna Station and years during 1940-2020.*

The obvious direct relation between Kinneret WL and precipitation regime in the watershed was documented widely in previous studies. Historical (9000 years before present) data of the Kinneret WL was investigated by two different methods [20, 21] and indicated an amplitude of 20 m (197–217 mbsl) WL fluctuations.

*Fractional polynomial regressions between annual means of daily maximum (left panel) and minimum (right* 

The discussion about dependence relations between phytoplankton and nutrients presented here emphasize the paradigm of an everlasting dilemma: Between phytoplankton composition and nutrient concentrations, who is the boss? (**Figures 7** and **8**) Algal community structure responds to the concentration of the nutrients or the contrary: does the nutrient concentrations is primary or secondary result of the algal density [6, 11, 23–33]? Nitrogen input is defined as predictor of algal domination in Lake Kinneret: Peridinium or Cyanobacteria. A decline of epilimnetic TN standing stock was documented during 1969 to 2001 accompanied by decline of Peridinium biomass while the biomass of Cyanobacteria increased. TN decline initiated Nitrogen deficiency, which is favored by Cyanobacteria [32] due to their ability of maintain the fixation of atmospheric Nitrogen by the enzyme of Nitrogenase. Earlier studies suggested two elements as key factors for the Peridinium bloom formation: Copper (Cu) and Selenium (Se) [6, 23, 29–33]. The study of the Cu impact was not thoroughly developed but that of Se did it thoroughly. It was confirmed that Se is a limiting factor of Peridinium growth. Before Hula drainage, the chemical conditions of the peat soil were mostly reductive but presently more oxidative and, therefore, limitation of Se is not impossible. Earlier Studies [29, 30], suggested that precipitation and runoff discharges are an important source of bioavailable Se (Selenites and Organic Se) and high availability of Se in surface waters of Kinneret watershed might be a significant supporter of the Peridinium heavy blooms. Therefore, it is suggested that in addition to Nitrogen deficiency, Se input decline affected the decline of Peridinium biomass. Conclusively, the replacement of Peridinium by Cyanobacteria is mostly due to change of nutrients dynamic resulted by climate change. The depletion of Nitrogen supply is based on a long-term record and the recorded data about Se dynamics is partial.

### **Figure 7.**

*Fractional polynomial regressions between annual averages of Epilimnetic loads (ton) of Total nitrogen (TN) (left), Total phosphorus (TP) (right) inputs through Jordan inflow and years.*

**Figure 8.**

*Fractional polynomial regressions between annual averages of phytoplankton biomass (g/m<sup>2</sup> ) (Peridinium, Cyanophyta) and years.*

### **4.3 Dam management: to open or not to open?**

Open or Not to Open (ONO) the South Dam when WL is high? That is the question for Sustainability by hydrological managers [23, 34, 35]. Regional trends of climate change and dryness process were recorded: Standard Precipitation Index (SPI) enhancement precipitation decline, air and lake water temperature increase, river discharges and restriction of lake input volumes and consequent decline of WL, elongation of RT duration. The decline of water availability for domestic and agricultural supply created a national concern accompanied by increase of Lake water salinity, epilimnetic Nitrogen deficiency and Phosphorus sufficiency which enhanced biomass replacement of Peridinium by Cyanobacteria [28]. These natural ecological modifications were accompanied since 2010 by replacement of the lake as principle supplier of drinking water by desalinization of mediterranean waters. The following additional parameters made the ONO dilemma more significant. Multiannual (1933–2020) daily record of WL indicates an average annual increase of 1.6 m. Nevertheless several annual exceptions of higher and/or lower of it are common. These exceptions are critical for decision makers with regard to the dynamics and management policy of water supply which was dependent of pumping rate and Dam management: high WL indicate pumping potential enhancement and low WL dictate withdraw restrictions. Several cases which represent not common conditions are: During fall 2001 WL was lowered to the lowest altitude ever recorded since 1933–214.87 mbsl and pumping was exceptionally restricted; during winter 1969 WL increased up to 208.2 mbsl and the dam was maximally opened; Five hydrological years (October–September next year) 2013/2014–2017/2018 were a drought sequence in a row when the annual increase of the WL varied between 0.35 and 1.58 m. At the end of this drought period the epilimnetic salinity was 325 ppm Chloride which was even predicted to increase higher if dryness trend would be continued. Three years earlier (2011–2013) the WL annual elevation varied between 1.75 and 2.58 m. After five drought seasons (2014–2018) heavy rain winters came and WL elevation was 3.41 in 2019 and 3.0 m in 2020. In December 2019 when WL was 211.89 mbsl, salinity was measured as 325 ppm. chloride. Later on in winter 2019 the heavy input discharges during January – mid-March when dam was closed dilution effect resulted salinity decline to 273 ppm chloride, (52 ppm decline). It is likely that enhanced water exchange (RT shortening) by open dam might cause higher decline of salt concentration. Moreover, it is also predicted to enhance nutrients and Microcystis biomass removal which enhance improvement of water quality. Since late 1990's the phytoplankton assemblages are dominated by Cyanobacteria, mostly due to the toxic Microcystis spp. The recent lake situation is

**131**

*Sustainable Utilization of the Lake Kinneret and Its Watershed Ecosystems: A Review*

therefore creating a dilemma for future management of sustainability: Water supply is done by desalinization, while salinity and Microcystis are enhanced supported by close dam and RT elongation water quality is therefore deteriorated. It is likely that, within future design for sustainability other than hydrological factors must be included. For example, salinity, nutrients and toxic Cyanobacteria biomass Consequently, during rainy winter a partial open of the dam is recommended aimed

The salinity of Lake Kinneret water was a critical parameter when supply for agricultural utilization was actually required. The major supply of salt to the lake are fluxed through the lake bottom through two major process: surface infiltration (superficial) and welling up. Salts' contribution through rivers and tributary inflows are much lower in comparison the sub-lacustrine sources. The salinity of River Jordan (65% of total inflows) is more than 10 times lower than that of the lake. Nevertheless, until late 1950's about 25% (total about 160000 tons annually) of salt input came through the runoff of two hot-salty springs located close to the north-western lake shoreline. Those two springs were diverted (1967) and about 40,000 tons of salt were eliminated from the lake budget. As a result of this anthropogenic implementation accompanied by the heavy floods during the winter of 1968–1969 (25% of lake water were exchanged) lake water salinity declined from 400 to 210 ppm Chloride. Historical information indicates Chloride concentration range before the 1950's between 290 and 325 ppm. A critical question is therefore arise: why salinity was increased during 1948–1968 from 280 to 400 ppm Chloride when negligible consumption of lake water was supplied for domestic and agricultural usage and the only one management tool, Dam operation (NWC was not in use yet) was available? The WL record indicates an increase of more than 2 m during 20 years (1948–1968). It is therefore suggested that Dam operation policy was aimed at long-term water accumulation causing WL elevation accompanied by Salt accumulation which resulted significant concentration increase of Chloride by more than 100 ppm. It has to be noted that during 1948–1968 there was also a sequence of several drought seasons in a row. Conclusively, for 20 years, the water exchange was low resulting elongation of Residence Time duration. The 1948–1968 event is a case study example for future consideration of sustainability design. The case study of 1948–1968 was not the only one for future consideration. Two other closely related cases which continued only one winter each are relevant: During two

winters with heavy rain, in 1968/69 and 1991/92 similar inputs of 1 × 109

storage for supply is not critical resulted by desalinization supply.

fluxed into the lake during 2 months. The difference between the two winters was the Dam operation [23, 34]: During the first winter the Dam was maximal open and during the second winter completely closed. It has to be considered that the input of low salinity river waters into the much higher salt concentration of lake water create a dilution effect in winter and salt concentration in the lake decline but the level of the decline is dependent on two parameters: input volume and water replacement dynamic and the level of replacement is the dependent of open Dam policy. Results indicated that open Dam operation enhanced water replacement (exchange) which is in fact Residence Time shortening. Therefore during the winter of 1968/69 the Chloride concentration declined by 64 ppm while in the winter of 1991/92 the decline was smaller – 39 ppm. It is therefore recommended to enhance water exchange (shorter Residence Time) through open Dam or pumping regime to remove salt and other pollutants (including biomass of Cyanobacteria) if water

 m3 were

*DOI: http://dx.doi.org/10.5772/intechopen.93727*

at quality improvement.

**4.4 Salinity**

*Sustainable Utilization of the Lake Kinneret and Its Watershed Ecosystems: A Review DOI: http://dx.doi.org/10.5772/intechopen.93727*

therefore creating a dilemma for future management of sustainability: Water supply is done by desalinization, while salinity and Microcystis are enhanced supported by close dam and RT elongation water quality is therefore deteriorated. It is likely that, within future design for sustainability other than hydrological factors must be included. For example, salinity, nutrients and toxic Cyanobacteria biomass Consequently, during rainy winter a partial open of the dam is recommended aimed at quality improvement.

### **4.4 Salinity**

*Landscape Architecture - Processes and Practices Towards Sustainable Development*

*Fractional polynomial regressions between annual averages of phytoplankton biomass (g/m<sup>2</sup>*

Open or Not to Open (ONO) the South Dam when WL is high? That is the question for Sustainability by hydrological managers [23, 34, 35]. Regional trends of climate change and dryness process were recorded: Standard Precipitation Index (SPI) enhancement precipitation decline, air and lake water temperature increase, river discharges and restriction of lake input volumes and consequent decline of WL, elongation of RT duration. The decline of water availability for domestic and agricultural supply created a national concern accompanied by increase of Lake water salinity, epilimnetic Nitrogen deficiency and Phosphorus sufficiency which enhanced biomass replacement of Peridinium by Cyanobacteria [28]. These natural ecological modifications were accompanied since 2010 by replacement of the lake as principle supplier of drinking water by desalinization of mediterranean waters. The following additional parameters made the ONO dilemma more significant. Multiannual (1933–2020) daily record of WL indicates an average annual increase of 1.6 m. Nevertheless several annual exceptions of higher and/or lower of it are common. These exceptions are critical for decision makers with regard to the dynamics and management policy of water supply which was dependent of pumping rate and Dam management: high WL indicate pumping potential enhancement and low WL dictate withdraw restrictions. Several cases which represent not common conditions are: During fall 2001 WL was lowered to the lowest altitude ever recorded since 1933–214.87 mbsl and pumping was exceptionally restricted; during winter 1969 WL increased up to 208.2 mbsl and the dam was maximally opened; Five hydrological years (October–September next year) 2013/2014–2017/2018 were a drought sequence in a row when the annual increase of the WL varied between 0.35 and 1.58 m. At the end of this drought period the epilimnetic salinity was 325 ppm Chloride which was even predicted to increase higher if dryness trend would be continued. Three years earlier (2011–2013) the WL annual elevation varied between 1.75 and 2.58 m. After five drought seasons (2014–2018) heavy rain winters came and WL elevation was 3.41 in 2019 and 3.0 m in 2020. In December 2019 when WL was 211.89 mbsl, salinity was measured as 325 ppm. chloride. Later on in winter 2019 the heavy input discharges during January – mid-March when dam was closed dilution effect resulted salinity decline to 273 ppm chloride, (52 ppm decline). It is likely that enhanced water exchange (RT shortening) by open dam might cause higher decline of salt concentration. Moreover, it is also predicted to enhance nutrients and Microcystis biomass removal which enhance improvement of water quality. Since late 1990's the phytoplankton assemblages are dominated by Cyanobacteria, mostly due to the toxic Microcystis spp. The recent lake situation is

*) (Peridinium,* 

**4.3 Dam management: to open or not to open?**

**Figure 8.**

*Cyanophyta) and years.*

**130**

The salinity of Lake Kinneret water was a critical parameter when supply for agricultural utilization was actually required. The major supply of salt to the lake are fluxed through the lake bottom through two major process: surface infiltration (superficial) and welling up. Salts' contribution through rivers and tributary inflows are much lower in comparison the sub-lacustrine sources. The salinity of River Jordan (65% of total inflows) is more than 10 times lower than that of the lake. Nevertheless, until late 1950's about 25% (total about 160000 tons annually) of salt input came through the runoff of two hot-salty springs located close to the north-western lake shoreline. Those two springs were diverted (1967) and about 40,000 tons of salt were eliminated from the lake budget. As a result of this anthropogenic implementation accompanied by the heavy floods during the winter of 1968–1969 (25% of lake water were exchanged) lake water salinity declined from 400 to 210 ppm Chloride. Historical information indicates Chloride concentration range before the 1950's between 290 and 325 ppm. A critical question is therefore arise: why salinity was increased during 1948–1968 from 280 to 400 ppm Chloride when negligible consumption of lake water was supplied for domestic and agricultural usage and the only one management tool, Dam operation (NWC was not in use yet) was available? The WL record indicates an increase of more than 2 m during 20 years (1948–1968). It is therefore suggested that Dam operation policy was aimed at long-term water accumulation causing WL elevation accompanied by Salt accumulation which resulted significant concentration increase of Chloride by more than 100 ppm. It has to be noted that during 1948–1968 there was also a sequence of several drought seasons in a row. Conclusively, for 20 years, the water exchange was low resulting elongation of Residence Time duration. The 1948–1968 event is a case study example for future consideration of sustainability design. The case study of 1948–1968 was not the only one for future consideration. Two other closely related cases which continued only one winter each are relevant: During two winters with heavy rain, in 1968/69 and 1991/92 similar inputs of 1 × 109 m3 were fluxed into the lake during 2 months. The difference between the two winters was the Dam operation [23, 34]: During the first winter the Dam was maximal open and during the second winter completely closed. It has to be considered that the input of low salinity river waters into the much higher salt concentration of lake water create a dilution effect in winter and salt concentration in the lake decline but the level of the decline is dependent on two parameters: input volume and water replacement dynamic and the level of replacement is the dependent of open Dam policy. Results indicated that open Dam operation enhanced water replacement (exchange) which is in fact Residence Time shortening. Therefore during the winter of 1968/69 the Chloride concentration declined by 64 ppm while in the winter of 1991/92 the decline was smaller – 39 ppm. It is therefore recommended to enhance water exchange (shorter Residence Time) through open Dam or pumping regime to remove salt and other pollutants (including biomass of Cyanobacteria) if water storage for supply is not critical resulted by desalinization supply.
