Article Type : Opinion Article
Authors : Moshe Gophen
Keywords : Lake Kinneret
As the only
multipurpose natural freshwater Lake in Israel, Lake Kinneret management is a
national concern. Cornerstone events in the History of the lake and its
drainage basin management include: 1933-construction of a Dam on the River
Jordan outlet; 1964 -inauguration of the National Water Carrier which removed
daily about one mcm (million cubic meters; 106 m3);
1967-Operation of salty waters (about 20 annual mcm with about 40,000 ton)
removal system; 1994- Harmful Cyanobacteria (HFCB) invasion and domination
decline of the bloom forming Peridinium spp.; 1980`s trophic status shifting
from Phosphorus to Nitrogen limitation; 2010-National supply of desalinized
water for domestic demand and consequently diminished of Kinneret withdraw; A
brief consideration of the implementation of Limnological principles within
management design of combined utilization and quality protection in Lake
Kinneret is presented.
As the only
multipurpose natural freshwater Lake in Israel, Lake Kinneret management is a
national concern. Cornerstone events in the History of the lake and its
drainage basin management include: 1933-construction of a Dam on the River
Jordan outlet; 1964 -inauguration of the National Water Carrier which removed
daily about one mcm (million cubic meters; 106 m3);
1967-Operation of salty waters (about 20 annual mcm with about 40,000 ton)
removal system; 1994- Harmful Cyanobacteria (HFCB) invasion and domination
decline of the bloom forming Peridinium spp.; 1980`s trophic status shifting
from Phosphorus to Nitrogen limitation; 2010-National supply of desalinized
water for domestic demand and consequently diminished of Kinneret withdraw; A
brief consideration of the implementation of Limnological principles within
management design of combined utilization and quality protection in Lake
Kinneret is presented.
Some of the Kinneret Hydrological parameters assembled with respect to the impact of climate condition changes on the hydraulic trait of Lake Kinneret (Tables 1 and 2).
Year |
Annual Mean WL (mbsl) |
Annual Water Input (mcm/y) |
Annual Mean Lake Volume
(mcm) |
HRT (years) |
1969 |
208.87 |
1099 |
4471 |
4.1 |
1992 |
209.32 |
842 |
4302 |
5.1 |
2001 |
214.11 |
254 |
3484 |
13.7 |
2015 |
212.45 |
141 |
3822 |
27.1 |
2019 |
211.54 |
160 |
3986 |
24.9 |
Period |
Mean Lake Volume (mcm) (106 m3)) |
Annual Mean of water input
(Jordan River) (mcm/y) |
HRT (years) |
Periodical WL amplitude
(mbsl) |
1988-1991 |
4217 |
358 |
11.8 |
210.40-208.89 |
1995-2003 |
4059 |
338 |
12 |
211.06-209.72 |
2005-2010 |
3823 |
381 |
10 |
210.86-212.66 |
2014-2019 |
3660 |
235 |
15.6 |
212.84-213.36 |
Mean WL: The average between Highest and Lowest recorded WL.
MBSL: Meter
below Sea Level (Lake Kinneret is located below sea level)
MCM: million
cubic meters (106 m3)
HRT is defined as the ratio between water input
and lake volume un-affected by water level.
Recent proposals of the Kinneret hydrological
management are aimed at enhancement of water supply for irrigation in the Hula
Valley (northern to lake Kinneret), to the state of Hashemi Jordan, to Eastern
part of Israel (Arava Valley), and to the West-Bank. A recent implementation of
an annual addition of 60 - 100 mcm desalinized water to the lake create an
agro-limnological dispute: direct desalinized water into lake Kinneret and pump
lake water for agricultural demands in the Hula Valley or direct desalinized
water for irrigation not through the lake. There is a significant
hydro-limnological and financial difference between these two management options.
The evaluation of limnolgical principles is required in order to maintain a
setting between those two controversial implementations: the difference between
long-term (multiannual) and short-term (annual or seasonal) modifications within
the ecosystem structure. Taking Kinneret water salinity as an example, the
following background conditions are consider: most of the salt import into Lake
Kinneret originate from sub-lacustrine uncontrolled sources and salinity of
runoffs is lower by order of magnitude from that of the lake. Consequently,
short-term seasonal changes of salinity are decline during winter floods and
increase later. Nevertheless, in spite of seasonal concentration decline
resulted by winter floods, the total load capacity is increasing (Figure 1).
Not like salt concentration, its load inventory is not fluctuate (ups and
downs) by seasonal water balance changes and continually increase or stay high
unless reduced by pumping or through open dam release. The limnological consequence
of pumping or open dam release is control implementation of the water exchange
rate defined as shortening of the Hydraulic Residence Time (HRT). Future
perspective of long term Kinneret water quality protection is therefore include
both input of desalinized water and pumping lake water as an additional supply
to the Hula Valley and/or other consumers. Three advantages are consequently
achieved: shortening of HRT, decline of total salt load capacity, additional
water allocation to the Hula Valley and other consumers, and financial
conditions improvement. Nevertheless, an optional disadvantage is also
predicted: salinization enhancement of the Peat-Soil in the Hula Valley.
Conclusively, water managers should consider the balance between soil salinization
risks versus prevention of lake water long-term deterioration. Elimination of
the soil salinization deterioration is already carried out successfully, since
early 20th century, by farmers cultivating field and grove crops in close
vicinity to the Lake Kinneret. Since the early 20th century, vast area is
efficiently cultivated by Lake Kinneret water irrigation. Partial soil
salinization is routinely treated by freshwater flushing. This case exemplify
an optimal combined implementation of limnology, agriculture. Financial merit
and human welfare.
If the rate of
discharge is enhanced. HRT become shorter. Nevertheless, shortening of HRT
occur also by lake water release (open dam) or pumping withdraw. Since the Mid
1980`s changes of climate conditions in the Watershed of Lake Kinneret were
documented: precipitations and river discharges decline, and temperature
elevation. Relevant recent hydraulic cases in Lake Kinneret are implicit to
comparable management under alternates of droughts and floods along the history
of Lake Kinneret. During the heavy rainfall in 1969 and 1992 the Dam was open
and close respectively. Similar quantities of water input, app. 1 billion m3
flew into the lake during the winter months in 1969 and 1992. But, in 1992 HRT
was longer because the Dam was closed and lake volume increased. Moreover,
Winter salinity declined by 64 ppm (300 to 236) and 39 ppm (250 to 211) during
1969 and 1992 respectively. It is therefore concluded that seasonal salinity
concentration might be even enhanced by close dam (smaller dilution resulted by
lower decline) and longer HRT as shown for 1992 dam management case. During
1948-2020 five temporal periods of increased salinity were indicated:
1948-1968, 1988 – 1991, 1995 – 2003, 2005 -2010 and 2014 – 2019. Whilst decline
was recorded during 1964 – 1988 resulted by the salty springs removal together
with the heavy flood event. The salty springs removal, refer to annual discharge
of 20×106 m3 and total salty load of app. 40,000 tons. It
is therefore suggested that significant increase of salinity during 1948-1964
(from 275 to 396 ppm) is due to close Dam policy which resulted HRT
prolongation, WL increase and enhancement of salt concentration and load.. The
salinity elevation afterwards were probably affected mostly by water balance
resulting HRT fluctuations. Results given in Table 2 indicates the irrespective
relation of HRT prolongation to WL (i.e. Lake Volume) but positively correlated
with water balance [1-3].
Two models (abbreviated
as: A and B) of salinization process dynamics in Lake Kinneret were defined: A
model attributed salinization dynamics to geo-hydrological dynamics of the
interphase contact between underground salutes and water flows in the aquifers.
The B model rely on the major function of water balance. The A model did not
evaluate data collected before 1960 and the B model verify field data before
1960. It is suggested that B is well adapted to short-term (days and weeks)
prediction when great runoff inputs enhance decline of lake salinity, whilst
for long-term period (months and years) when water retention time is long,
additional water migration through aquifers initiate salinity elevation as
predicted by A model. According to B, reduction of runoff inputs implies
salinity increase and A indicates that increase of salinity is the result of
water yield enhancement in the aquifers (enhanced by runoffs). The original
Kinneret salinity probably ranged between 250-350. Salinity fluctuation has
probably lesser impact on the biota (flora and fauna) of Lake Kinneret. The
phytoplankton is highly vulnerable to nutrient availability changes and to a
lesser extent to salinity per se. It is not impossible that freshwater algae
might be adapted to salinity changes of ups and downs but the amplitude ranges
has not definition yet, as well as salinity decline. Kinneret salinity was
lowered from 400 ppm in 1967 to 200 ppm during the early 1980’s, and the
phytoplankton composition was fairly stable and significant change came 30
years later when Nitrogen deficiency and N/P mass ration was developed. Then,
the domination of the bloom forming Peridnium spp. diminished and Harmful
Cyanobacteria enhanced. To achieve reasonable protection of Lake Kinneret
ecosystem, an outlined target of salinity below 350 ppm is accepted. If the
usage of the Kinneret waters would be mostly directed towards agricultural
irrigation, it is probably cheaper to control salinity by the less expensive
operation of hydrological conditions than the expensive processes of salts
removal.
One Year test case that was documented by Mekorot, National water Supply Company, Laboratory and Kinneret Watershed Unite in an interim annual report: October 2018-October 2019 is given here in (Figure 1).
Figure 1: Linear regression (95% Ci and regression parameters are given) between monthly means of Chloride concentration (ppm) and Total load (tons) in Lake Kinneret during October 2018 – October 2019.
This Information
indicates the followings: during winter months (short-term) Chloride
concentration was lowered by 39 ppm whilst documentation of annual (long-term)
change represent an increase of 36,000 tons of salt lads to loads in Lake
Kinneret. This conservative load would enhance salt accumulation in the Lake
unless partly removed through pumping or Dam spilling. Nevertheless, total
annual pumping withdraw was 136.2 mcm (106 m3) which is
about three times lower than earlier removals. The annual natural evaporation
of pure water that was estimated as 254.3 mcm has no impact on the lake load.