Watershed Planning Notes

Utility of Hydrologic Data in Watershed Planning

Use of Hydro-meteorological Data

  • Hydro-meteorological data includes precipitation, abstractions, and other meteorological parameters.
  • Data requirements vary based on watershed planning objectives, such as:
    • Hydrological characterization.
    • Flood management and control.
    • Irrigation and drainage.
    • Groundwater planning.
    • Water quality management.
    • Fisheries and eco-conservation.

Hydro-meteorological Data in Hydrological Characterization

  • Focuses on rainfall, river flow, and groundwater measurement and analysis.
  • Rainfall data is essential for assessing the interaction between rainfall, river, and groundwater.
  • Climate data includes precipitation, temperature, and evaporation.
  • Evaporation data is measured using evaporation pans or estimated via evapo-transpiration, often using the Penman-Monteith Equation (requires air temperature, humidity, solar radiation, wind speed, and day length).

Data Presentation and Management

  • Basic level: catalogue approach presenting statistics related to locations and areas.
  • Requires a lead agency for website maintenance, updates, content, access control, and query management.
  • Operational role: data feeds necessary at short intervals for tactical applications.
  • Evapo-transpiration (ET) estimation requires air temperature, atmospheric humidity, radiation balance, and wind speed integration over a daily period.

Hydro-meteorological Data in Flood Management and Control

  • Planning and design fall under planning and infrastructure agencies.
  • Operations (flood forecasting and warning) are managed by water management or meteorological agencies.
  • Data needed: daily and sub-daily rainfall, wind velocity, and direction.
  • Flood plain zoning identifies risk categories for planning and development.
  • Coastal flooding factors: tide, wind speed/direction, atmospheric pressure; storm surges in specific physical structures.

Hydro-meteorological Data in Irrigation and Drainage

  • Strategic level involves national planning with meteorological and water management agencies as key data providers.
  • Daily data tables include variables for potential evapo-transpiration calculation.
  • Supply sources: surface water and groundwater.
  • Requires meteorological forecasts (medium and long term) for managing supply.
  • Automatic Weather Stations (AWS) can provide enhanced information for demand scheduling and ET estimation.

Hydro-meteorological Data in Groundwater Planning

  • Important in arid and semi-arid climates.
  • Groundwater characterized by annual drawdown and recharge cycle.
  • Confined aquifers show delayed response to rainfall.
  • Groundwater recharge occurs during rainy seasons after soil moisture deficit (SMD) is replenished.
  • Groundwater flooding occurs when water levels rise above ground level due to extended high rainfall.

Hydro-meteorological Data in Water Quality Management

  • Catchment management is the responsibility of water management agencies.
  • Addresses chemical, biological, and physical characteristics.
  • Water pollution incidents depend on meteorological conditions.
  • Combined sewer overflows (CSOs) during heavy rainfall can cause untreated sewage spillage.
  • Dilution manages waste discharge with residual impurities; rainfall frequency and dry weather duration are vital.
  • Salinity and sedimentation are exacerbated during droughts.

Hydro-meteorological Data for Fisheries and Eco-Conservation

  • Fisheries depend on water quality maintenance.
  • Requirements include temperature monitoring and drought forecasting.
  • High temperatures combined with low flow can stress or kill fish stocks.
  • Conservation involves physical and biological relationships in water-bodies and wetlands.

Use of Physiographical Data

  • Includes Topographic data, Land use-land cover data and Soil data

Utility of Topographical Data

  • Involves data on physical/ natural features of the watershed, watershed boundaries, floodplains, wetlands and water bodies.
  • For hydrological characterization, the data on slope, permeability of the ground surface, roughness of the ground surface, obstructions is required.
  • For flood management and control, the data on wetlands and water bodies, channel cross sections, other natural and artificial flood mitigation structures is required.
  • For irrigation and drainage, data on optimum water table depth, canal linings, canal flow capacity, crop type, crop area are necessary.
  • For groundwater management, the data on annual changes in water table depth, crop root zone depths, wetlands and water bodies is needed.
  • For water quality management, the locations of point and non-point pollution sources, total maximum daily loads (TMDLs), spatio-temporal variations in pH, turbidity, total suspended solids, total dissolved solids, biochemical oxygen demand (BOD) etc. May be needed.
  • For fisheries and eco-conservation, the data on dissolved oxygen, spatio-temporal variations in aquatic plants and animals having eco-conservation capabilities is required.

Utility of Land Use/ Land Cover (LULC) Data

  • Data consists of data on forests, grass/ range lands, cultivated lands, orchards, wildlife reservations, recreation areas, urban/ rural areas, water bodies, eroded areas etc.
  • LULC influences interception, infiltration, surface runoff, surface storage, groundwater runoff, groundwater storage, evapo-transpiration (ET).
  • LULC influences meteorological parameters such as temperature, humidity and wind velocity, which in turn impact the estimation of ET.

Utility of Soil Data

  • Soil data can be an important factor in determining the amount of erosion and storm water runoff that occurs in the watershed of interest.
  • It can enable the estimation of water retained within the soil, analyze the slope stability or the flow of groundwater through the soil pores.