Summary
Highlights
The video introduces the various hydrological components, including evapotranspiration, evaporation, infiltration, groundwater, interflow, interception, depression storage, precipitation, and runoff.
It clarifies that precipitation is any form of water falling from the atmosphere, while rainfall is a specific type of precipitation. Other forms include sleet, freezing rain, and snow. Surface runoff, the movement of water from the ground to a waterway, is affected by precipitation, infiltration, imperviousness, and land slope. Steeper slopes increase runoff, and urbanization's imperviousness also contributes. Surface runoff quantity is crucial for storm water management to prevent flooding and it also carries pollutants, causing water quality problems.
Surface runoff is measured using rainfall-runoff models, categorized into conceptual, metric, and physics-based models. Examples of conceptual models include ANN, TOPMODEL, HEC-HMS, SWAT, fuzzy, and tank models. Physics-based models include the GSSHA model. The I-HAT class model combines conceptual and physics-based approaches.
Evapotranspiration combines evaporation and transpiration. Evaporation is the transformation of liquid or solid water into a gaseous state, occurring on open water, soil, and vegetation. Transpiration is the release of water vapor from plant leaves through stomata. Evapotranspiration rates are influenced by temperature, wind, vapor pressure, plant characteristics, and soil moisture.
While evaporation plays a minor role in precipitation, evapotranspiration is vital for hydrologic budgets of catchments, lakes, and reservoirs. Evaporation can be measured using the Hargreaves method with a Class A pan, tracking daily water depth reduction. Evapotranspiration is commonly calculated using the Penman-Monteith method, which can be integrated with radiation-based or temperature-based analyses. Radiation-based methods generally show better performance with lower error rates and higher correlation.
Infiltration is the passage of water through the soil interface. Its rate is affected by rainfall duration, soil porosity, permeability, antecedent soil moisture, and vegetation. It's a critical process in urban stormwater management, and urbanization often reduces infiltration, increasing runoff volume and discharge. Approximately 4% of global land precipitation infiltrates the ground.
Groundwater flow is water moving towards a water body within the ground, a continuous process independent of the hydrological cycle. Groundwater can exist as confined aquifers or below the interflow layer, maintaining the base flow in some rivers. Urbanization can decrease groundwater flow due to increased imperviousness. Interflow, or subsurface flow, is water moving laterally beneath the land surface but above the groundwater table, continuing until it enters a waterway, water body, or is evapotranspired. Factors affecting interflow are similar to surface runoff. Interflow is rarely analyzed separately and is often lumped with surface runoff into 'direct runoff'.
Interception is influenced by precipitation type and amount, vegetation, and wind. It's generally not a significant process in urban stormwater management. Depression storage refers to precipitation detained, stored, and evaporated from depressions on the land surface. It's a small amount of water that doesn't run off or infiltrate, affected by surface type, slope, and evaporation factors. Due to its small magnitude, it is also not typically important in urban stormwater investigations.