Estimation of the infiltration/natural recharge to groundwater from rainfall is an important issue in hydrology, particularly in arid regions. This paper proposes the application of The Natural Resources Conservation Service (NRCS) mass balance model to develop infiltration (F)–rainfall (P) relationship from flash flood events. Moreover, the NRCS method is compared with the rational and the Ф-index methods to investigate the discrepancies between these methods. The methods have been applied to five gauged basins and their 19 sub-basins (representative basins with detailed measurements) in the southwestern part of Saudi Arabia with 161 storms recorded in 4 years. The F–P relationships developed in this study based on NRCS method are: F = 39% P with R2 = 0.932 for the initial abstraction factor, λ = 0.2. However, F = 77% P with R2 = 0.986 for λ = 0.01. The model at λ = 0.01 is the best to fit the data, therefore, it is recommended to use the formula at λ = 0.01. The results show that the NRCS model is appropriate for the estimation of the F–P relationships in arid regions when compared with the rational and the Ф index methods. The latter overestimates the infiltration because they do not take λ into account. There is no significant difference between F–P relationships at different time scales. This helps the prediction of infiltration rates for aquifer recharge at ungauged basins from monthly and annual rainfall data with a single formula.
Aquifer recharge from flash floods in the arid environment: A mass balance approach at the catchment scale
1. Aquifer recharge from flash floods in the arid environment:
A mass balance approach at the catchment scale
Mohamed Farran, Nassir Al-Amri and Amro Elfeki
Department of Hydrology and Water Resources Management, Faculty of Meteorology, Environment &
Arid Land Agriculture, King Abdulaziz University, P.O. Box 80208-Jeddah 21589, Saudi Arabia.
5. Problem Statement
It is very well-known that arid and semi-arid regions are lacking hydrological
measurements worldwide since the rare occurrence of rainfall events.
Moreover, there is always a limitation on the validity of rainfall-runoff models
in these regions.
In Saudi Arabia, a few research studies were undertaken for studying transmission
losses and infiltration rates from rainfall.
Therefore, any attempt to analyze the available data based on field
measurements in these regions will help the hydrological studies in the arid
region in general and the hydrological studies in SA in particular.
5
7. Objectives
7
The current study proposes two mass balance
approaches namely: the NRCS and the rational
methods to estimate the infiltration–rainfall
relationship.
Idea 1
Comparison is made between the proposed
methodologies and the literature from others.
Idea 2
come up with the best model that could be used
to describe the rainfall–infiltration relationship in
the arid region of SA.
Idea 3
The results are essential for accurate estimation
of the recharge rates for sustainable
developments of groundwater resources in SA.
Idea 4
8. Previous Studies
8
Allam and Balkhair (1987) Wadi Khat and
Wadi Jawf are subbasins of Yiba basin used
the phi (Ф) index method (93% of rainfall is
converted into recharge.)
Abdulrazzak et al. (1989) Tabalah basin using
a mass balance approach (75% of rainfall is
converted into recharge).
16. Methodology
01 The NRCS method-based mass balance approach (USDA-NRCS, 2004)
02 The rational method-based mass balance approach
03 Rainfall-Runoff Calculation
16
17. Methodology
17
The NRCS method-based mass balance approach (USDA-NRCS, 2004)
𝑭 = 𝑷 − 𝑸 − 𝑰𝒂
F is the cumulative infiltration (L),
P is the total precipitation (L),
Q is the direct runoff (L),`
Ia is the initial abstraction (L), and
𝑰𝒂 = 𝝀 𝑺
• λ is the initial abstraction ratio and
• S is the maximum retention capacity of the
basin (L),
𝑺 =
𝑷
𝝀
+
𝟏 − 𝝀 𝑸 − 𝟏 − 𝝀 𝟐𝑸𝟐 + 𝟒𝝀𝑷𝑸
𝟐 𝝀𝟐
𝑺 = 𝟓 𝑷 + 𝟐𝑸 − 𝑸 𝟒𝑸 + 𝟓𝑷
𝑪𝑵 = 𝟏𝟎𝟎
𝟐𝟓𝟒
𝑺 + 𝟐𝟓𝟒
λ = 0.2
18. Methodology (Cont)
18
The rational method-based mass balance approach
𝑸𝒑 = (𝒊 − 𝒇)𝑨 = (𝒊 − 𝒌𝒊)𝑨 = (𝟏 − 𝒌)𝒊𝑨 = 𝑪𝒊𝑨
i is the average rainfall intensity (L/T),
f is the average infiltration rate (L/T),
k is the recharge coefficient,
C is the runoff coefficient,
A is the area (L2), and
Qp is the peak discharge (L3/T).
𝑪 =
𝑸
𝑷
𝒌 = 𝟏 − 𝑪
= 𝟏 −
𝑸
𝑷
25. Conclusions
25
The NRCS mass balance model is appropriate for the
estimation of the infiltration-rainfall relationship at
catchment scale in arid regions when compared with
the rational method balance model or the Ф-index
method
Appropriate results of NRCS
The infiltration-rainfall relationships developed in this
study are: F = 39% P with R2 = 0.932 for λ =0.2,
whereas, F = 77% P with R2 = 0.986 for λ =0.01. The
NRCS mass balance model at λ = 0.01 exhibits a better
fit to the data when compared with λ = 0.2.
The infiltration-rainfall relationships
The main issue with the rational mass balance
model and Ф-index method that they do not take
the initial abstraction into account and therefore
they overestimate the infiltration rates.
Rational mass balance and Ф-index
There is no significant difference between infiltration-
rainfall relationships at different time scales. This helps
the prediction of infiltration rates for aquifer recharge at
ungauged basins from monthly and annual rainfall data
with one formula
Infiltration rates for aquifer recharge
