Forests and Water: A State of the Art Review for Colorado

• Year: 2003
• Title: Forests and Water: A State-of-the-Art Review for Colorado
• Author: Colorado State University
• Description: Colorado State University 2003
• Publications - Doc Type: Other

ently disparate results requires a basic understanding of
forest hydrology, including infiltration, interception, soil
moisture storage, and evapotranspiration. Different types
of forest disturbance and forest regrowth can affect each
of these processes in different ways, depending on the
site conditions, how a given management action is car-
ried out, and the hydrologic event of concern (e.g., annu-
al water yields, summer low flows, spring snowmelt, or
extreme rain events). Generalizations and extrapolations
can be misleading unless there is a clear linkage to, and
understanding of, the underlying processes.
There is a close relationship between forest condition,
runoff processes, and the quality of the water emanat-
ing from a forest. In general, forests grow in more
mesic areas and generate relatively little overland flow
at the hillslope scale (Dunne and Leopold, 1978). As a
result, forested areas commonly provide large amounts
of high- quality water (Dissmeyer, 2000). Poor forest
management practices can degrade the quality of this
water, while careful forest management can alter the
amount of runoff with little or no detectable effect on
water quality.
These generalizations apply to Colorado, as most of the
state's runoff emanates from forested areas at higher el-
evations, and this water is generally of very high quality.
Rapid population growth is increasing the demand for
water in urban areas, and this increased demand is illus-
trated by the rapid increases in the price of water along
the Front Range. Increasing water demands are also
emanating from industry, recreational interests, and the
desire to restore natural flow regimes to improve aquatic
habitat and support endangered species. Municipal water
suppliers are required to assess the risks to their sources
of water, and in most cases this means an assessment of
how forest conditions affect water quality. Substantial
amounts of public and private funds are being spent to
improve water quality and aquatic habitat. Given these
demands and issues, there is an increasing need for a
more rigorous understanding of how current forest con-
ditions and possible management actions can affect the
amount, timing, and quality of runoff.
Current forest conditions, water yields, and water quality
also need to be evaluated in a broader historical context,
as past changes in land use and forest composition are
directly and indirectly affecting the amount of runoff
as well as the quality of that runoff. For example, fire
suppression and low levels of forest harvest are believed
to have increased the density of forest vegetation and
reduced annual water yields in the North Platte water-
shed (Leaf, 2000; Troendle and Nankervis, 2000). The
increase in forest density can indirectly affect water
quality, as denser forests tend to be at greater risk to
high- severity wildfires. Large, high - severity wildfires
are of particular concern because they can greatly in-
crease the size of peak flows, hillslope erosion rates,
and downstream sedimentation rates (Tiedemann et al.,
1979; Robichaud et al., 2000). The effects of high- sever-
ity fires on runoff and water quality were dramatically il-
lustrated by the 1996 Buffalo Creek fire, where post -fire
flooding and erosion led to the loss of human life, severe
property damage, and greatly increased water treatment
costs (Agnew et al., 1997; Moody and Martin, 2001).
The large wildfires in 2002 focused public attention on
the changing wildfire risk due to prolonged drought and
high forest densities.
From a regulatory perspective, a detailed understanding
of the relationships between forests and water are needed
to meet the demands of several important pieces of en-
vironmental legislation. The National Environmental
Policy Act requires federal agencies to assess the likely
impact of proposed federal actions, including a larger -
scale assessment of potential cumulative impacts (CEQ,
1997). Regulations emanating from the Clean Water Act
and its amendments require a watershed approach to im-
prove water quality when water quality standards are not
being met despite the application of NPDES permits for
point sources and Best Management Practices (BMPs)
for nonpoint sources (EPA, 1991). The Endangered
Species Act (ESA) requires federal agencies to protect
endangered species and their habitat, and many of the
species of greatest concern are aquatic species that de-
pend on the water in, or emanating from, forested areas
(MacDonald, 2000). The net result is a renewed interest
and focusing of public attention on the interactions be-
tween forest management and the amount, timing, and
quality of runoff.
1.2. Objectives and Organization
The basic purpose of this report is to provide a state -of-
the -art summary on how forest management in Colorado
affects water quantity and quality, and to identify key
gaps in knowledge. This synthesis should help guide
public policy and decision - making, and help identify
future research priorities.
The preparation of this report was conducted under the
guidance of a panel of water managers and scientists.
This panel was first convened in April 2000, and the
specific objectives were defined as: