Hydrology and Environmental Engineering Notes

Importance of Engineering Hydrology

  • Focuses on crucial topics including rainfall, groundwater, water supply, and flood management.

  • Significant impact on populations living in flood or drought-prone areas.

  • Projections indicate that by 2025, two-thirds of the global population may face water stress.

  • Pollution of groundwater and water resources poses serious risks to human health.

Hydrological Cycle

  • Water Budget Equation:

    • P = Q + AET + G + riangle S + riangle G

    • Where:

      • P = precipitation (inflow)

      • Q = river flow (outflow)

      • AET = actual evapotranspiration

      • G = groundwater discharge

      • riangle S = change in soil moisture storage

      • riangle G = change in groundwater level

  • Water Table Analysis:

    • If the study period's beginning and end have constant water table height, riangle G = 0 and riangle S = 0.

Global Rainfall Data

  • Annual Average Rainfall

    • UK rainfall varies significantly (from <600 mm to >3000 mm).

    • Visual representation of intensity thresholds in millimeters highlights regional variation and average metrics across the globe and specific areas like the UK, based on data from 1981-2010.

Human Interventions in the Hydrological Cycle

  • Activities include:

    • Cloud seeding

    • Irrigation practices

    • Urbanization and its effects

    • Deforestation and its impact on soil and moisture retention

    • Issues like soil erosion and desertification

    • Consequence of acid rain and ozone layer depletion.

Sustainable Development Goals (SDGs)

  • Identify interconnected SDGs impacted by construction and civil engineering:

    • Clean water and sanitation, climate action, sustainable cities, and responsible consumption and production.

Climate Change and Water Needs

  • Drivers of Sustainability

    • Factors influencing climate change include:

    • Rising global temperatures leading to increased extreme weather events.

    • Diminished basic city services, infrastructure, and human health impacts.

    • Higher energy and water demands in multiple sectors influenced by climate dynamics.

Global Warming and Its Effects

  • Causes of Global Warming:

    • Increase in greenhouse gases like CO2 and CH4 are primarily due to human activities.

    • Effects of climate change manifest globally and locally through variations in temperature and precipitation.

Precipitation Characteristics

  • Analysis of Intense Rainfall Events:

    • IDF (Intensity-Duration-Frequency) curves represent the varying return periods or frequencies of storm occurrences.

  • Rainfall Hyetograph:

    • A graphical representation of rainfall intensity over time to assess total precipitation.

Evaporation Dynamics

  • Definitions:

    • Potential Evapotranspiration (PET) represents max water loss assuming ample water supply.

    • Actual Evapotranspiration (AET) is the actual loss that takes into account limitations in moisture.

Infiltration and Percolation Processes

  • Distinguish between infiltration (initial penetration of water into the ground) and percolation (vertical movement through soil layers).

  • Methods of measurement include utilizing double ring infiltrometers.

Surface Runoff Dynamics

  • The natural movement of water over land driven by gravity.

  • Hydrographs record water levels or discharge over time and indicate flood characteristics.

Factors Affecting Surface Runoff

  • Key contributors include climate conditions, antecedent moisture, land cover, slope, and soil characteristics.

  • For example, vegetation increases infiltration but reduces immediate runoff, while saturated soils enhance runoff rates.