HEALTH AND SANITATION
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A summary of the comparison between the four models
is presented in Table 5.3, according to:
• Temporal scale — refers to the time step of the input
data and used in the model [sub-hourly (+/-), hourly
(+/-), daily (+/-), monthly (+/-), annually, flexible]. Rank
[1-3]: models with flexible time step that include the
daily time step receive the highest rank 3; models
working at the daily time step get 2; and models with
time steps higher than the daily time step get 1.
• Length of rainfall input data — refers to the length
of the rainfall time series used to run the model
[1 year; 10 years; > 10 years]. Rank [1-3]: 3 for
models with long time series (> 10 years), 2 for
models with time series longer than 5 years but
shorter or equal to 10 years, and 3 for models with
short time series (1 year).
• Length of water demand input data — refers to the
volume of water extracted from the tank [flexible,
time series, fixed value]. Rank [1-3]: 3 for models
with flexible demand (both fixed and time series),
2 for time series of water demand, and 1 for fixed
water demand.
• Process modelled — refers to all processes that
are modelled (reliability, optimum tank size). Rank
[1-6]: (1-3 for each process); 6 if both processes
are modelled, 4 if only one process is modelled,
and 1 if none of the processes are modelled.
• Cost — refers to the price of the model in rands
and the cost of the required system to run it. Rank
[1-3]: 3 for public domain models with free or cheap
platform, 2 for public domain models running on
expensive platforms, 1 for models which cost money.
• Data requirements — refers to the input data
(beside the roof area, the rainfall time series and
the water demand) that the model requires in order
to run. Rank [1-3]: 1-high, 2-medium, 3-low.
• Expertise — refers to the scientific skills required
to use the model adequately [low, medium, high]:
3-low, 2-medium, 1-high.
• Technical support — support available for setting
up the model, calibration and use. Rank: [1-3]:
3-if full support is available, 2-if limited support is
available, 1-if there is no support.
• Documentation — refers to the available
documents of a model, such as reference manuals,
user guides, web pages [good, medium, bad]. Rank
[1-3]: 3-good, 2-medium, 1-bad.
• Ease of use — refers to the user friendliness of the
computer-based model, taking into consideration
graphical user interface (GUI), input-output (I/O)
operations, and visualisation options [easy, medium,
and difficult]: 3-easy, 2-medium, 1-difficult.
• Operating system — refers to the operating system
required for the effective use of the model [Linux,
UNIX, MAC, Windows CE, 95, 98, 2000, XP, 7, 8].
Rank [1-3]: 3 for Windows-based applications since
Windows 7, 2 for DOS applications and windows
operating systems before Windows 7, and 1 for
Table 5.3: Comparison of selected RWH models,
following evaluation criteria developed after
•
•
•
•
other operating systems.
Validation — indication of whether or not the model
results can be validated against observed data.
Rank [1-3]: 3-validated, 1–not validated.
Advantages and disadvantages — summarises the
merits and demerits of a given model. Rank: [-].
References — lists the key reference(s) to the
model in the literature. Rank: [-].
The total score gives the sum of all ranked criteria.
MODELLING USING THE SHORTLISTED RWH
MODELS
The roof, SamSamWater rainwater harvesting tool, yield
reliability analysis, and the raincycle model were used to
Figure 5.1: Modelling results of the roof, YRA, SamSam, and
raincycle in Cape Town, Durban, Pretoria, and Stellenbosch.
Continued on page 35 >>
www.plumbingafrica.co.za
February 2019 Volume 24 I Number 12