Small Decentralized Hydropower Program National ... - Cd3wd.com

Otros, tales coma el Modelo Sacramento y el SHE
(Sistema Hidroldgico Europeo) existen ai igual que
otros que han sido desarrollados para aplicaciones
especificas. Pero, para generar promedio mensual
todos estos modelos tienden a ser mbs detallados que
ei nivei de information normalmente disponible.
El tipo de modelo a escoger es generalmente deter-
minado por el tamaiio de la cuenca, Las cuencas
pequeiias probablemente seran I-I& adecuadas para
representation por ioe mod&s basados en gran
cantidad de detalles fkicas. A medida que el area a
cubrir aumenta usualmente hay necesidad de emplear
unidades de tiempo mas grande en las computaciones
asi que 10s coeficientes y par&metros tienden a
alejarse de o a perder su significado original.
Finalmente, existe un deseo natural de usar
modelos cuyos valores de coeficientes y parametros
puedan ser facilmente transferidos de una region de
valores conocidos a otra con datos insuficientes. Tal
sofisticacion presumida seria muy conveniente. Sin
embargo, coma lo dice Body (1980), este no el el case
todavia:
“Se han desarrollado muchos modelos que intentan
describir la forma de las relaciones que existen en
una cuenca. En algunos cases ciertos modelos
pueden pro’reer excelentes resultados para pro-
positos especificos tales coma la extrapolation de
series de tiempo. Sin embargo, es aparente que
ningun modelo ha&a ahora ha tenido exito en
proveer un esquema en el que las caractetisticas de
la cuenca puedan ser inclmdas con la confianza de
que con las series de tiempo producidas se pro-
veeran par&metros mas exactos que 10s derivados
por el metodo de regresibn.”
Medidas de1 Terreno. Como al escribir este
articulo no se ha tenido la intencidn de que se lo
utilizara coma manual de campo, no se tratara sobre
10s detalles para las medidas hidrometricas. Muchos
libros y manuales dan excelentes g-Gas sobre 10s
diferentes metodos para medir las corrientes (por
ejemplo, Buchan y Somers, 1969, o Alward, et. al,
1977). Para las de instalaciones gigantes e! procedi-
mientos para in&alar escalas hidrometricas pro-
bablemente implicara esfuerzos considerables de
parte de un equip0 de individuos tkcnicamente
entrenados para ello. Para loas instalaciones de
plantas de mini hidroenergia, el proceso, en la
mayoria de 10s cases, sera eject&ado por personas
relativamente inexpertas. Las g-Gas a que nos
referimos anteriormente serviran para instruir
satisfactoramente a e&as personas en las tkcnicas
requeridas.
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One must also determine, as quantitatively as
possible, whether the period during which the
measurements were made was wet or dry. In
general, the procedures mentioned before for cor-
relation with other areas will apply, however, this
ievel of sophistication will probably not occur
with most mini-hydro developers. In fact, it is
probably unnecessary in most instances since
the question most frequently being asked is the
availability of firm power during periods of
critical streamflow. For that estimate only a
lower limit is required - and in many cases the
amount of flow in a stream will exceed that
which the developer would wish to divert for
power. On the other hand, high flow periods may
be equally important since during those periods
the effective head for small impoundments may
prove to be so low as to be of no value in
generating electricity. This point should not be
overlooked and may be important in considering
installation designs.
What If You Have No Data?
Because the title of this section is one which
is raised regularly, in particular, by those
interested in developing mini-hydro units, it
needs careful consideration. First of all, in the
absence of any data (quantitative or qualitative),
one would be well advised not to invest any
funds whatsoever. On the other hand, it would be
a rare situation that would preclude any
investigation that could provide some guidance.
The point is, if no specific data exists at your
site, you should apply the type of techniques
described earlier. Site visitation is always
required - one should never consider a
hydrologic study complete without site verifica-
tion. Would it not be a professional waste of time
(not to mention a personal embarrassment) to
find that months of regional correlation, etc. were
valueless because the basic map erroneously
showed the stream flowing in the wrong
direction?
Furthermore, site visitations should be used to
verify office calculations. And site visitations can
provide considerable qualitative information con-
cerning the history of flow variation: flood plain
location, vegetative growth variations, material
lodged in trees from previous high flows, etc. The
best maps, in any case, may offer only educated
guesses as to the true ground contours. Trees
often grow much better (and taller) in the low
areas - and maps (even aerial photographs) will