Report
of Recharge Experiment
Introduction
A number of years ago, Professor Ken Rushton developed an
algorithm. It is now being used to develop a spreadsheet involving the soil
moisture accounting data to estimate the runoff (RO), actual evaporation (AE)
and soil moisture deficits (SMD). In the method, recharge can be obtained by
the data of RO, AE and SMD.
Experiment
In this experiment, Daily rainfall(P) and potential
evaporation(PE) are the meteorological inputs which are public data. There
might be a situation that PE data is given by month. The PE data can be assumed
to follow a linear relationship to make it possible to calculate. After the raw
P and PE data are received, they can be used after a mathematical adjustment.
As the first step, Runoff (RO) can be estimated from
precipitation on the daily P and SMD from the previous day. Here come the
different RO equations when the value of P is in different intervals. When the
value of P is greater than 10, RO is determined not only by the value of P but
also by the value of SMD. The clear equations following different conditions
are as below,
if P<5mm, then there is no runoff
if 5<P<10 then RO=0.2(P-5)
if 10<P<20 then,
*if SMD<10 then RO=0.2P
*if 10<SMD<30 RO=0.1P
*if 30<SMD<60 RO=0.05P
*if 60<SMD RO=0
if 20<P then,
*if SMD<10 RO=0.3P
*if 10<SMD<30 RO=0.2P
*if 30<SMD<60 RO=0.1P
*if 60<SMD RO =0.05P
As the second step, it is necessary to estimate actual
change (AS). There are the relationships between AS and the potential change
(PS). The numerical relationship is also determined by SMD with root constant
(C) and wilting point (D).
if PS>0 and C<SMD<D then AS=0.1PS
if PS>0 and D<SMD then AS=0
Others, AS=PS
The PS can be calculated by the equation as PS=PE+RO-P
As the third step, when the AS is obtained, the soil
moisture deficit shall be updated as below,
SMDnew=SMDold+ AS
As it is known, the recharge (R) is the amount reduction.
The absolute value of R is equal to the absolute value of SMDnew. Hence,
-SMDnew is the amount of recharge.
There are two equations to describe the relationships among
R, SMDnew, SMDold and AS.
SMDnew=max ( 0, SMDold+AS)
R=SMDnew-SMDold-AS
The final step is to use the equation AE=AS+P-RO to
calculate the actual evapotranspiration (AE).
After all the calculating and estimating in the spreadsheet,
the check shall be down as below,
When, P=RO+AE+R+ difference of SMD, it is a correct
estimator.
Otherwise, it failed.
Results
The final estimators are as below,
RO(mm)
|
P
|
1032.80
|
||
87.10
|
Runoff
|
111.82
|
10.8%
|
|
AE
|
428.11
|
41.5%
|
||
C
|
76 mm
|
Recharge
|
492.865
|
47.7%
|
D
|
12 mm
|
D_SMD
|
0.000
|
|
Balance
|
0.00
|
Conclusion
The experiment shows that the spreadsheet developed based on
the algorithm of Professor Ken Rushton is functional. The recharge is possible
calculated by the public data of daily rainfall and potential evaporation.
PS: The idea of artificial recharge of aquifers. Here attaches a link,
