WATERSHED CHARACTERISTICS AND PROFILING Flashcards
Quantitatively and qualitatively expressed ___________ are basic to the understanding of and control over the various hydrologic processes in a watershed.
watershed characteristics
A good knowledge on watershed characteristics will help in:
a. predicting or estimating maximum flow,
b. minimum flow and average flow of a stream, even overland flow which are useful information in erosion control, design and
c. construction of engineering structures and planning, design and selection of watershed management strategies.
THE WATERSHED CHARACTERIZATION PROCESS:
a. geomorphological characteristics, b. soil characteristics,
c. climatic characteristics
d. run-off variables
e. vegetation
f. wildlife
g. land use
h. socio-economic features and geology.
GEOMORPHOLOGICAL CHARACTERISTICS:
- Basin Shape
- Area
- Basin length
- Slope
- The shape of a watershed mainly governs the rate at which is supplied to the mainstream as it travels along its course from the source to the mouth.
- This has significant effect on the profile and channel dimensions.
Basin Shape
The ______ of watershed can be measured by using a planimeter or any other method available.
area
The boundary of a watershed is delineated by following the ridge surrounding the watershed on a topographic map. This boundary is called a ___________.
topographic divide
This is known as axial length or the maximum ______. Generally, this is measured from the outlet of the basin to the remotest point of the drainage boundary or divide
basin length
The ______ of a watershed has important influences on infiltration, surface runoff and groundwater contribution to stream flows.
slope
SOIL CHARACTERISTICS:
- Soil texture
- Soil structure
- Permeability
- Internal soil drainage
- Erosion condition
- refers to the relative proportions of the various size groups (or separates) of individual soil grains.
Soil texture
An example of soil texture classification is as follows:
sand, loamy sand, sandy loam, loam silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay.
- refers to the aggregation of primary soil into compound particles or clusters of primary particles which are separated from adjoining aggregates by surfaces of weakness.
Soil structure
Strcture shape is described as being:
platy, prismatic, columnar, angular, blocky, subangular blocky, granular, or crumb.
- is the quality of soil that enables it to transit water or air.
Permeability
- is the quality of a soil that permits the downward flow of excess water.
Internal soil drainage
- Erosion status in the watershed is important in identifying priority areas requiring immediate attention.
- It is also a way evaluating the suitability of land uses and the effectiveness of various conservation strategies.
Erosion condition
- Meteorology data of a watershed is important because of its great influences on almost all hydrological process.
Climatic Features
The following climatic factors are usually characterized in describing a given watershed:
precipitation, air temperature, air humility, wind movements, solar radiation, evaporation, soil temperature and pressure.
- are important indicators of the impacts of various activities in the watershed.
Runoff variables
Some of the most commonly monitored runoff parameters are:
annual streamflow, peakflow, minimum flow, sedimentation, dissolved chemical constituents (such as Ca, HCO, NO, and Na); micro- organisms (e.g. fecal coliform and fecal streptococcus); and physical and chemical properties (like temperature, conductivity, pH, and salinity).
The type and structure of plant community in a watershed is necessary to the understanding of the roles vegetation plays in the physical processes of a watershed
Vegetation
One of the major concerns in watershed management is _______ conservation
wildlife
To be able to properly manage the wildlife population in the watershed, the species ________, species ______, species _________, species ______and_______ should be assessed carefully.
composition; density; distribution/occurrence; diversity and similarity
- is a major source of alternations in a watershed.
Land use
Survey of land uses could either be done in the or in the office using recently taken ___________.
aerial photographs or satellite imageries
- The human component in a watershed ecosystem is one single component which profoundly influence the sustainable or destruction of the watershed.
- Anthropogenic activities can cause disturbances on the biophysical processes within the watershed in fashion and magnitude beyond that which can be attributed to climate upheavals and other similar phenomena.
Socio-economic features
In describing the socio- economic features of a watershed, it is important to remember that there are two major groups of people which have to be considered, namely:
- the watershed occupants or onsite watershed beneficiaries, and
- the offsite watershed beneficiaries.
Phases of Watershed Management:
a. Situational Analysis
b. Objectives Identification
c. Management Planning and Plans
d. Management Plan Implementation
e. Management Plan Revision
- Collecting existing data is the first step toward comprehensive survey and planning of a watershed.
Situational Analysis
preparation of a watershed profile:
- Background information and history of the area
- Project Description
2.1. Biophysical Data
2.2. Socio-economic Data
2.3 Issues and Problems
Biophysical Data:
- Project location and area
- Accessibility
- Topography
- Geology and Soil- types
- Vegetation and land uses
- Water uses
-climate
Socio-economic Data:
- Communities/HH in the area
- Gender Description
- Source of living
-Density/ Population
- Before starting formal survey, preparatory investigation is often needed.
- The main purpose is to identify major watershed problems and collect or check preliminary information.
Objectives Identification
The usual activities in objective identification may include:
- collecting first-hand information
- using available photos, maps and other data to become familiar with watershed conditions
- interviewing local agencies, institutions, communities
Physical problems:
Steep slopes
Slide-prone soils
Erosion due to heavy rainfall
End problems:
Heavy sedimentation
Water pollution
Resource use problems:
Shifting cultivation
Deforestation
Socio-economic problems:
Poverty among watershed inhabitants
Low acceptance of innovative conservation practices
Management Planning and Plans:
- Preparatory Planning
- Work Plan/ Proper Planning
Preparatory Planning:
- Identify the topographic boundaries
- Organize multi-disciplinary planning team specialist from the different stakeholders
Work Plan/ Proper Planning:
a. Formulation of plan
b. Budgetary Allotment
c. Manpower Requirements
d. Management of Survey Plan
e. Nursery establishment Plan
f. Reforestation Plan
g. Land Uses
g. Forest Protection Plan and Implementation of Soil and Water Conservation
Management Plan Implementation:
- Nursery establishment
- Reforestation and Land uses
- Forest Protection and Implementation of Soil and Water Conservation measures
