1. INTRODUCTION
The Jordan Rift Valley (JRV) refers to the depression below the sea
level extending over the range of latitudes 30-33 N and longitudes 35-36
E, including Lake Tiberias to the north and the Dead Sea in the middle,
surrounded by Jordanian Highlands and Judaean Mountains. Due to the arid
environment as compared with the other parts of Jordan, as mentioned in
Tarawneh and Kadıoğlu (2003), the management of irrigation water is
vital in JRV (Al-Weshah 2000). However, available data of precipitation
and streamflows in JRV are limited to monthly resolution, significantly
hindering efficiency in modeling with widely used hydrological
methodologies (Rumman et al. 2009). An innovative water harvesting (WH)
system has been established for research purposes in the Lisan Peninsula
of the Dead Sea (Unami et al. 2015). The geology of the Lisan Peninsula
is detailed in Closson et al. (2007). A barren catchment area of = 1.12
km2, as shown in Figure 1, yields flash floods several
times a year, and hydraulic structures have been constructed at the
outlet to harvest them as designed in Sharifi et al. (2015). The water
current is fully collected at a gutter cutting across a 16 m wide valley
bottom and then guided to an open-air reservoir of 1,000
m3 capacity through a conveyance channel of 60 m long
(Unami and Mohawesh 2018). The conveyance channel is equipped with a
spillway to release excess backwater from the reservoir. As there is no
authorized guideline in Jordan, an arbitrary flood discharge of 1,000
L/s is used in the hydraulic design of the spillway. A solar-driven
desalination plant, having a blackish water reservoir of 300
m3 capacity in a modified greenhouse, treats the
harvested water to be used for irrigation (Unami et al. 2020), and
year-round farming is performed under optimal water management policy
(Unami et al. 2019). The available lands somewhat constrain the
capacities of the reservoirs, but the open-air reservoir is large enough
to buffer the brackish water to be sent to the desalination plant after
siltation. An observation system is operating since September 30, 2014,
so that time series data of rainfall and runoff in flash flood events
are minutely acquired (Figure 2). Due to the extremely arid environment,
water current as the runoff from the catchment is ephemeral, and the
flash flood events are clearly distinguishable from each other.
Figure 1. Photo of the gorge in the barren catchment area
Figure 2. Photo of the observation system including VAISALA WXT536
weather transmitter and SR50A acoustic distance sensor for measurement
of runoff discharge
This Scientific Briefing presents a statistical analysis of flash flood
events observed at the observation system, in order to provide basic
knowledge of hydrology in JRV to be utilized for designing WH systems.
The duration, the rainfall depth, and the runoff coefficient of each
flash flood event are standard hydrological parameters, but the most
critical parameters for designing WH systems are the spillway design
discharge and the reservoir capacity (Walsh et al. 2014). The
correlations among those parameters as random variables are firstly
analyzed in terms of the classical methods of Pearson’s correlation
(Pearson 1896) and Spearman’s rank correlation (Spearman 1910). Then,
probability distribution fitting is performed for each variable,
focusing on the lognormal distribution with three parameters (LN3) (Levy
and Kroll 1976) and the generalized extreme value distribution (GEV)
(Jenkinson 1955) in particular. Fundamentals and recent developments in
estimating the probability of extreme events from independent
observation are presented in Makkonen and Tikanmäki (2019). The results
support the design of the WH system, which has been already constructed
with arbitrary hydrological parameters, providing quantitative
information for designing and operating WH systems in the future as
well.