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

coma pesticidas en las aguas recibidas, dependiendo
de su fuente de origen. Estos materiales, y la reduc-
cion de la productividad primaria a menudo causan el
agotamiento de1 oldgeno corriente abajo de 10s
lugares de la construction.
Al depositar materia sS,lida en suspension se
puede eliminar ciertas comunidades b6nticas al enter-
rar las plantas y animales, alterando el substrato y
obstruyendo las agallas y las estructuras colectoras
de alimentos de insectos acuaticos. Los impactos
adversos a 10s peces resultan a consecuencia de: (1)
d&o y engruesamiento de1 epitelio de las agallas,
causando dif’icultad en la respiration y en la funcidn
regulatoria de la sal; (2) reduction de la resistencia a
otras tensiones tales coma enfermedades, productos
qtimicos toxicos, reducida cantidad de otigeno
disuelto, y aumento de la temperatura, (3) reducida
disponibilidad de alimentos y deterioramiento de1
comportamiento alimenticio; (4) crecimiento en pro-
portion deprimida; y (5) reduction potential en la
capacidad reproductiva causada por el ya mencionado
bloqueo de la m;gracion, sedimentation depositada
sobre 10s nidos donde 10s peces deposi&n sus huevos,
supresion de1 comportamiento reproductor, y aumen-
to de la mortalidad de 10s huevos que son enterrados
y tambien debido a la reducida disponibilidad de
oxigeno disuelto.
Hay otros impactos potenciales relacionados con el
dique. La evaporation, el escurrimiento, la seguridad
de1 dique y esquistosomiasis son algunas de las cues-
tiones que se deberan estudiar durante la
planificacibn. Habra un aumento en la pkrdida de1
agua por causa de la mayor superficie de1 area de un
reservorio, particularmente en zonas de alta inci-
dencia solar. Tambien podra haber p&dida de1 agua
de1 reservorio por causa de1 escurrimiento en 10s
suministros de1 agua de1 suelo, dependiendo de la
cantidad de humus, arena y arcilla en el tipo de suelo
y la porosidad de 10s substratos geologicos. Tambien
es de importancia critica la seguridad de1 dique con-
tra sabotaje, destruction y aCin m&s importante,
terremotos. La disminucion de1 tlujo puede tambien
favorecer la diseminacidn de la esquistosomiasis.
Los diques obstaculizan la migracidn de peces. Las
escaleras para peces han sido desarrolladas extensa-
mente en 10s Estado Unidos y otros pa&es, especial-
mente por m&do de prueba y errores durante
muchos anos. El cost0 de una escalera para 10s peces
puede ser substantial, variando tipicamente de 8% a
12% o 15% de1 costo total de la construccibn. Hay
cases en que dicho cost0 puede ser mucho menor o
83
or most importantly, earthquake is also critical.
The decreased flow may also be favorable to the
spread of schistosomiasis.
Dams prevent fish migration. Fish ladders have
been developed extensively in the U.S. and other
countries, mainly through trial and error over the
years. Cost for a fish ladder can be substantial,
typically ranging from 8% to 12% or 15% of the
total construction cost. There are cases in which
this cost could be much lower or much higher,
depending on circumstances.
The impacts from the construction of facilities
for diversion systems, run-of-river and irrigation
systems are similar to those of dams but with
less intensity and, most importantly, no impound-
ment. A diversion system consists mainly of an
inlet structure in-stream, a diversion canal or
pipeline, usually a settling basin, a penstock, a
powerhouse with turbine/generator and outlet
works. Sedimentation from construction and ter-
restrial habitat disturbance or loss from clearing
for the powerhouse and access road or path are
the major diversion impacts. A run-of-river facility
consists of a low head dam with turbine and
generator within or close by. The dam may
impound some water but the main purpose is the
location of the generating equipment. Major
run-of-river impacts result from sedimentation
from construction and terrestrial habitat loss
from clearing. Use of turbines at sites of abrupt
changes in channel elevation of irrigation
systems with substantial flow cause the least
construction impacts, chiefly because the water
system is an artificial one devoid of life and
designed as a conduit for water to crops.
The impacts of a retrofit project are of con-
siderably less intensity than those of a new pro-
ject. There are three possible retrofit cases. The
first case is a site which has a hydropower
facility already operating and the purpose is
either to replace the existing equipment or to add
additional turbine(s) and generator(s). Replacing
equipment causes no impacts. Addition of equip-
ment requires expansion of the powerhouse, a
minimal impact.
The second case is an abandoned site. There
may be a range of impacts here. If the site is a
diversion facility, the rehabilitation of the equip-
ment, powerhouse and structure would cause
only minimal terrestrial habitat disturbance -
some sediment may find its way into a stream. If
the site is an old power dam, more significant im-
pacts may result from rehabilitation. Silt remova;