Water Level Fluctuation Patterns
The lake water levels fluctuated by yearly amplitude (WLamp ± SD) of
2.25 ± 2.00 m from 1956 to 2020. Consequently, a LOWESS plot showed that
the lake water level annual amplitude fluctuated during the period 1956
to 1975 and then decreased steadily up to its lowest level in 1989 (
amplitude = 0.1 m), with a subsequent increase to peak amplitude in 2008
(9.4, m) before a decreasing fluctuation between 2008 and 2021 (Figure
3). Linear regression analysis showed a non-significant (p =
0.12) negative relationship between yearly amplitude and time while the
waveform Sine 3 parameter modeled as Wlamp =2.328*sin
(2*ℼ*year/43.45+6.28) unlikely revealed a significant result () even
though p < 0.05 but r² = -0.64 indicating a poor fit
than a horizontal line. The trends in water level fluctuations as
measured by DLTM (Figure 4) were poorly explained by linear regression
model (p = 0.1229, r2 = 0.059). However, the
waveform Sine (3 parameter) model: DLTM = 1.376*sin (2*ℼ*year/(42.98 +
6.28)) was highly significant although with a weak fit (P <
0.0001, r² = 0.21), and indicated peak rise in water levels after every
⁓20 years (Figure 4).
The depth frequency plot (Figure 5a) showed that for 25% of the years
(1956-2021), the average depth of the lake was about 2 m while, for 20%
of the years, the average depth was 3 m. For less than 10% of the
years, the mean depth of the lake reached 4 m. Additionally only for
less than 5% of the years, the lake means depth ranged between 10-14 m
during the period from 1956-2021. The lake depth-area relationship
showed significant dependence (R2 = 0.74) of the lake
depth on its area (A, km2) modeled as: depth =
0.179e0.019A; Figure 5b. Thus, in current conditions,
a 1m increase in lake depth leads to a ~90 km2 increase in lake area with likely influence on
the riparian communities through overflows.