Watershed Greening and Soil Characteristics

Vegetation and Watershed Management

• Detailed vegetation information is essential for selecting appropriate methods for greening watersheds.

Physiographic Characteristics

Soil

• Sandy soils absorb more runoff water, resulting in reduced flow rates.
• Clay soils have lower absorption capacities, leading to increased runoff.
• Soil properties such as depth, type, moisture, and fertility influence crop growth.

Geology

• Rock structure dictates watershed formation, affecting size, shape, drainage, and groundwater conditions.
• Geological features, like cracks in rocks, can facilitate rapid underground water flow.
• Lakes, swamps, and storage systems help manage excess rainfall.

Hydrology

• Availability and quality of surface water are crucial for successful greenery growth in watersheds.
• Hydrological factors, including rainfall intensity and duration, define water quantity in a watershed.
• Prolonged low-intensity rainfall leads to increased evaporation and percolation, minimizing runoff.

Hydrogeology

• Groundwater is vital for irrigation, drinking, and industrial needs due to its purity.
• Understanding aquifer characteristics (nature, thickness) aids in watershed planning.

Socio-Economic Characteristics

• Surveys of local populations should assess their needs, economic conditions, health, livestock, farming practices, and management participation.
• Watersheds classified by land use include:
  • Agricultural
  • Urban
  • Mountainous
  • Forest
  • Desert
  • Coastal
  • Mixed (combinations of the above)

Types of Watersheds

Agricultural Watershed

• Dominated by agricultural activities and experiences significant land-use changes.
• Increased runoff and erosion can result from compaction during barren periods.

Urban Watershed

• Characterized by buildings and infrastructure, reducing natural infiltration and increasing runoff.
• Vulnerable to flooding due to altered natural drainage patterns.

Mountainous Watershed

• Higher altitudes result in substantial snowfall and high surface runoff.
• Downstream areas are prone to flooding from snowmelt in warmer seasons.

Forest Watershed

• Natural forest cover provides significant interception and moisture retention.
• Stability classifications: fragile, unstable, moderately stable, stable, based on various biophysical and socio-economic indicators.

Watershed Classification

• Classification based on size, shape, location, groundwater exploitation, and land use.
• Two watersheds of similar size may behave differently if land use or channel types vary.

Size Classification

• Small Watersheds: < 250 km²; overland flow is dominant.
• Medium Watersheds: 250 to 2500 km²; accessible and well-balanced.
• Large Watersheds: > 2500 km²; channel phase is prominent with lower sensitivity to short-duration rainfall.

Land Use Characteristics

• Land use affects hydrological processes and runoff rates.
• Variability in climate and physiographic conditions influences land exploitation patterns.

Climatic Characteristics

• Dry conditions before rainfall increase infiltration and evapotranspiration losses.
• Intensity and duration of rainfall directly impact peak flow rates.
• Accurate peak flow assessments are critical for hydraulic structure design (e.g., dams, weirs).

Hydrographic and Drainage Characteristics

• The hydrographic network includes all watercourses influencing runoff.
• Key factors affecting the hydrographic network: geology, climate, relief, and environment.
• The classification of rivers based on stream order aids in understanding watershed dynamics.

Vegetation Cover

• Vegetative cover reduces peak flow by retarding flow and enhancing infiltration.
• Essential for protecting soil from erosion and managing runoff effectively.