Modeling

10 Rules for Responsible Modeling
C Compute evaporation loss.
C=====================================================================
IF(METRIC.EQ.1.AND.STORE.GT.0.0) QQEV(I)=AREA*E(MONTH)/1036800.0
IF(METRIC.EQ.2.AND.STORE.GT.0.0) QQEV(I)=AREA*E(MONTH)/8.64E7
STORE1 = STORE - QQEV(I)*DS
IF(STORE1.LE.0.0) THEN
QQEV(I) = STORE/DS
STORE1 = 0.0
ENDIF
C+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
CALL INTERP(SST,SDE,JINT,STORE1,DEPTH)
C+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2700 IF(NP.LE.0) GO TO 5000
IF(IROUTE(I)) 4000,4000,3000
C=====================================================================
snip
Following development of the source code, the program is debugged and
compiled into executables and then linked into an executable (.EXE) program
that can be run on certain hardware and operating systems, often a task in itself.
When run, the program computes a solution that steps out in time, a class of
problem referred to as initial value problems. At each step there is an iteration
to solve the equations.
Summary: We have conveniently dodged the vast subject of numerical
analysis, which fits between Step 3, derivation of the fde's, and Step 4,
development of the executable program. Nevertheless the above description
describes how our models are typically built. It is a creative endeavor often
fraught with error from beginning to end, and results in very long codes
(SWMM44GU has about 50,000 lines of code including 15,000 comment lines,
while the shell PCSWMMGIS2002 alone probably runs to over 200,000 lines).
The creative art in programming models is not well appreciated by the
public, who may consider engineers to be pedestrian and unimaginative. In the
long, dry code, that initial, conceptual, brief spark of creative genius is key.
1.4 When to use a model
Models are used to supply or fill in missing data or information. As a design
tool, a WSM for example usually provides credible information about the
relative performance of alternate arrangements of storm water management
facilities. Analysis of the information provides knowledge of the various
systems. As stated earlier, if the engineering community had innate knowledge
of the long-term environmental performance of proposed large, complex, urban
drainage and pollutant removal systems (and if the engineers were infallible),
then modeling would of course be unnecessary. But urban storm water drainage
systems are sometimes both extensive, incorporating more conveyances and
devices than can be comprehended, and sometimes exceedingly complicated,