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

loqueo de las especies migratorias, particularmente
de 10s peces. Los impactos terrestres mas substan-
ciales son la perdida de las viviendas de animales pe-
quenos en 10s campos y la selva por causa de la
inundation y la construction de caminos y la casa de
mgquinas. La esquistosomiasis es un problema de
salud pdblica siempre que se creen depositos de agua
estancada.
Hasta cierto punto es posible mitigar estos impac-
tos, particularmente 10s relacionados con la corriente.
La sediment&on puede ser parcialmente controlada
mediante la ereccidn de barreras riparias y mediante
el uso de cuidadosas prgcticas en la construction. La
migration de peces aguas arriba puede ser asistida
mediante la construction de una escalera para peces,
una serie de escalones con propiedades fkicas
adecuadas para que 10s peces 10s puedan utilizar.
Qperacibn
De las tres configuraciones principales, de conten-
cion, corriente de1 tie, y desviacion, la que tiene mas
significativos impactos de operation son las asociadas
con la contention.
Ecologia Acuhtica. El uso de1 agua puede ser
indirectamente afectado por el agua almacenada,
particularmente para energia de punta. El acopio de
agua puede producir flujos de pulsation, i.e., periodos
de flujo por debajo de lo normal cuando se acumula
el agua y petiodos de alto flujo cuando se produce
energia. Aunque la operation aprovechando la cor-
riente de1 rio por desviacion serian m&s comunes
para las pequenas facilidades de baja caida, algunas
facilidadcs acopiaran el agua, y 10s flujos de pulsation
pueden afectar el uso de la corriente y todo sistema
viviente agua abajo.
El tipo y severidad de estos impactos dependeran
de !as condiciones pre-existentes, cambios en el punto
de retorno de1 agua y otros factores especificos de1
lugar. La salida de1 agua de las turbinas tipicamente
produce considerable turbulencia en el 5rea de salida
de1 agua. Esto a menudo requiere la construction o
renovation de una camara de establizacion inmediata-
mente debajo de la salida. Las c&maras de
estabilizacion van forradas de concrete o rotas para
absorber la energia turbulenta de las aguas de
retorno. La turbulencia por debajo de las salidas de
la turbina puede derrumbar y corroer la base,
especialmente debajo de las camaras de estabiliza-
cion. Esto puede introducir sedimentos en suspension
y alterar el ambiente agua abajo coma se menciono
anteriormente. Los efectos son m&s pronunciados
debajo de 10s diques mayores y con operacidn de
almacenaje.
87
Below small/low-head dams both of the im-
pacts discussed above are less likely to occur.
During flood flows, dams are often opened to
allow maximum discharge. Often, flood waters
flow over the dam crest, the tailwater rises, and
power generation becomes impossible. At worst,
low-head dams may slightly diminish the inten-
sity of flood flows. In reservoirs where water is
stored, power generation will cause variation in
downstream flow, but flow variations and conse-
quent ecological impact should be smaller than
for larger impoundments. Many low-head hydro
plants will have run-of-river operation and negli-
gible impact due to variation in flow.
Deep water discharge may have lower, more
constant temperature, lower dissolved oxygen,
higher concentrations of plant nutrients, other
dissolved solids, and dissolved gases including
hydrogen sulfide. Each of these factors can af-
fect downstream organisms and the various com-
binations of factors can produce many different
ecological patterns below impoundments. Low
dissolved oxygen concentrations can severely
reduce populations of fish and benthos, espe-
cially the exclusively riverine species. Thermal
constancy can cause lower diversity of benthos.
If dissolved oxygen is not limiting, tailwater
areas can be extremely productive. Often,
however, low dissolved oxygen and high concen-
trations of plant nutrients combine to produce a
zone of low biological diversity and marginal-to-
poor water quality. Hydrogen sulfide forms only
under completely anaerobic conditions, but it is
toxic to fish at rather low concentrations.
The problems of hypolimnetic release should
be less common and less severe at low-head
impoundments than at high-head impoundments.
Stratification can be more easily disrupted in a
shallow reservoir. The problems with deep-
release discharge can often be prevented or
mitigated. If problems are anticipated, discha.rge
outlets can be designed to allow selective with-
drawal, although this is often expensive.
Operation of turbines, particularly at dams, can
cause adverse impacts to organisms passing
through the turbines, especially fish which are
migrating downstream. The problems likely to be
encountered at small/low-head facilities are
substantially less severe than problems of large
hydro plants. Passage through turbines exposes
organisms to abnormal pressure, turbulence, and
mechanical forces. Organisms can be exposed to
abrasion, mechanical injury by wicket gates and