Watershed Inventory
Understanding the physical,
chemical and biological features and processes that affect water and its
movement is an essential first step in developing a watershed plan. A watershed inventory provides the basis for
evaluating impacts from proposed watershed management actions.
Physical features and landforms.
Watershed planners
need to understand bedrock geology
and surficial geology. The nature
of the underlying rock determines the character of the overlying soils and
influences water movement through the drainage of soils. The chemical properties
of the rock are important through processes of rock weathering, in which water flowing over the
rock is affected by the chemistry of the rock. Check the Geologic Survey of Canada for
more information.
Generally,
overlying the bedrock is a layer of softer sediments, or soils. Soil
composition determines soil chemistry, and physical properties such as drainage
characteristics and fertility. Detailed topographic maps are an excellent
source of information about the degree, shape and length of slopes (important
in controlling runoff and erosion).
Climate
Climate, including
temperature, wind force and direction, and precipitation influences water
resources and biological processes in a watershed. Information about solar
radiation, maximum and minimum air temperature, and related measurements can be
found from national weather services, libraries, universities and government
agencies. Check Environment
Canada’s Weather Office for information.
All water in a
watershed comes from precipitation. Rainfall measures tries to collect
information about the duration of a rainfall event, as well as its intensity,
or rate. Key challenges to collecting rainfall data are ensuring both a
representative sample and that sufficient area is sampled for an accurate
picture.
Wind conditions
may affect land and water processes, particularly evapotranspiration and wind erosion. Wind
conditions are highly variable, as a result of topography and structures. Wind speed and direction are generally measured
with an anemometer. Check Environment Canada’s Weather Office for information.
Soils, Infiltration, and Runoff
Soil is the porous
medium that covers bedrock. Its ability to transport water depends on the
size and condition of channels through the porous medium. These factors depend
on the size of soil particles, the degree to which individual soil particles
are aggregated into larger masses, and the arrangement of individual particles
and aggregates. Soils are classified based on permeability,
infiltration rate, and surface runoff potential.
Streamflow
Streamflow is the
rate of flow of water and is expressed in units of volume per unit time (e.g.,
m3/second). Streamflow can be calculated by determining the
cross-sectional area of the stream at the location of interest and the velocity
of that flow.
Groundwater
Groundwater is the
water that has passed through the land surfaces into underlying rocks and soils.
This region contains both saturated and unsaturated zones.
An aquifer is
defined as a saturated permeable geologic underground stratum that can transmit
significant quantities of water, and an aquitard as a less permeable layer that
may be significant to regional transport of water. Most aquifers are formed of
unconsolidated materials including stone and gravel. The top of the saturated
zone forms a “water table.” Groundwater is measured by injecting and tracking
tracer materials in the groundwater, by the use of field permeameters, or by
drilling into the aquifer and determining the pressure of the flowing water.
Groundwater is
discharged into surface waters at the land-water interface. Groundwater is
therefore a major contributor to the base flow for most surface waters. The
chemistry of water moving through an aquifer is altered by reaction with
chemicals in the soil, adsorption onto soils in the aquifer, bacterial action,
and similar processes.
Groundwater quality
is affected by water chemistry (acid-base reaction,
redox reactions, adsorption-desorption)
and local sources such as malfunctioning septic systems, leaking below ground
manure storage systems, sanitary landfill sites, land application of sewage
sludge’s and manures, and similar processes. These activities can convey bacteria,
viruses, parasites, and cysts into groundwater along with nutrients and solids.
Water Quality
Almost all water
users are affected by the quality of water. Chemistry of bedrock and surficial
geology, drainage characteristics of the soil, physical processes (e.g.,
erosion), and biological processes influence water quality. Acceptable water
quality levels are dictated by the use for the water.
Water quality
indicators may be physical, chemical or biologically. Physical indicators of
water quality include:
Chemical indicators
of water quality include:
Biological
indicators of water quality include:
·
Bacteria: faecal coliform, total coliform, or faecal streptococcus assays are
often used to indicate faecal pollution in water. Sources of bacteria and
viruses primarily involve the faeces of warm-blooded animals, e.g., sewage
treatment plant effluent, stormwater runoff, sewer overflows, and animal
wastes. All sources are effected by precipitation.
·
Parasites: Schistosoma sp. (parasitic
worms), Giaridia lamblia, and Cryptosporidium are the most common
parasites that have serious health implications for humans and other animals.
Plant and Animal Communities
Watersheds are
affected by a variety of biological processes. Therefore, an inventory should:
- Determine the number and types of plant
and animal species present in a watershed area;
- Estimate the number of individuals of
each species; and
- Investigate the interrelationship
between the species and their abiotic environment.
This information
may be found by a review of existing data or new data may be required. The
latter is time consuming and costly.
Land Use
The term land use implies use by humans, which
may change the landscape for purposes of resource extraction and processing,
housing and transportation. Changes to the land system can alter drainage
regimes, pollutant sources and yields, valued natural and built features, and
community priorities.
Assessment of land
use has three main elements:
·
An
understanding of the nature of human activities currently practised in the
watershed.
·
An estimate
of the areal extent of each activity (and perhaps its proximity to valued
watershed features).
·
The
ways in which the two previous points are likely to change in the near and far
future. The element of time is very important in understanding land use.
When compiling a
current land use inventory, check with your local and regional government
planning and zoning departments, topographic or road maps, agricultural
extension professionals, and satellite or high altitude aerial photography from
local libraries and universities.
Different land uses
alter the land in different ways. Land use may also be important in determining
applicable legislation, oversight agency, and interested non-governmental
organizations. General categories for land use include open space (rural,
non-agricultural, undeveloped land), forested/woodlot, parkland, agricultural
(rangeland and cropland), residential, commercial, and industrial. These
categories may be further sub-divided.
Social and Economic Systems
Social economic
systems are the human systems or infrastructure that overlay the natural and
built environment. These systems affect the attitudinal and economic forces and
community support that are central to the implementation of watershed
management. Social and economic systems influence a watershed by:
·
Influencing the attitudes and priorities of
watershed residents and decision-makers.
·
Affecting the value that may be placed on
individual watershed features and activities, and thus the importance they are
given in watershed planning.
·
Constraining the financial resources available
to resolve watershed issues.
Social and economic
systems can encompass commercial and industrial activity, major institutions
(such as hospitals and universities), religious systems (social significant
structures (e.g., temples) and belief systems), and residential development.
Social and economic stability or “quality of life” is also very important in a
community.
Information about
social and economic systems is often qualitative rather than quantitative.
Sources of information include census surveys (average household income, age
and sex distribution, spending patterns, and religious preference), local
Chamber of Commerce, public interest groups, service clubs, and community
leaders.
Valued Features and Activities
Values features and
activities are often unremarkable to the casual observe. They exist in each
watershed, and will be defended fiercely by local residents. An example of a
valued feature is a historical site or even a rock formation. An inventory of
valued features is best compiled with the assistance of local residents,
interest groups, historical societies, community leaders and similar
individuals.
Type of watershed
information that should be gathered when developing a watershed profile
includes:
·
species status, trends (e.g., presence of
endangered/threatened species, etc.)
·
water uses (e.g., fisheries, recreational, etc.)
·
land use (e.g., recreational areas, forestry,
urban, etc.)
·
watershed description and condition
§
drainage area
§
annual water flow
§
geomorphology
§
water temperature
§
channel morphology
§
sediment load
·
past habitat assessments
·
Chow, V., D.R. Maidment, and L.W. Mays. 1988. Applied
Hydrology. New York: McGraw-Hill.
·
Environment Canada Weather Office web-site: http://www.weatheroffice.ec.gc.ca/canada_e.html
·
Geologic Survey of Canada web-site: http://www.nrcan.gc.ca/gsc/index_e.html
·
Heathcote, I. 1998. Integrated Watershed
Management: Principles and Practices. John Wiley and Sons, Inc., ISBN
0-471-18338-5.
·
Magurran, A.E. 1988. Ecological Diversity and
its Measurement. London: Croon Helm.
·
Novotny, V., and H. Olem. 1994. Water
Quality: Prevention, Identification, and Management of Diffuse Pollution.
New York: Van Nostrand Reinhold.
·
Tchobanoglous, G., and E.D. Schroeder. 1987. Water
Quality: Characteristics, Modelling, and Modification. Reading, Mass.:
Addison-Wesley.
·
van der Leeden, F., F.L. Troise, and D.K. Todd.
1990. The Water Encyclopedia. 2d ed. Chelsea, Mich.: Lewis Publisher.
·
Viessman, W. 1990. Water management issues for the nineties. Water Resources
Bulletin 26(6): 883-891.
·
Viessman, W., Jr., and G.L. Lewis. 1996. Introduction
to Hydrology. 4th Ed. New York: Harper Collins College
Publishers.
