Hydrology Notes PDF

# Hydrology ## Chapter 1: Introduction to Hydrology as a Science - Hydro means Water. - Logy means Science. - Hydrology means "The science of water." ## Hydrology - Deals with the occurrence, circulation and distribution of water of the earth and earth's atmosphere. ## Importance of Hydrology in C...

# Hydrology ## Chapter 1: Introduction to Hydrology as a Science - Hydro means Water. - Logy means Science. - Hydrology means "The science of water." ## Hydrology - Deals with the occurrence, circulation and distribution of water of the earth and earth's atmosphere. ## Importance of Hydrology in Civil Engineering - **Hydrologists** (people who study Hydrology) apply their expertise to address water pollution, protect water resources, and contribute to engineering solutions. - Hydrologists focus on securing water supplies, designing irrigation systems, controlling flooding and erosion, and preventing water pollution, using scientific knowledge and mathematical methods. - Civil engineers rely on the data and expertise provided by hydrologists to design, construct, and manage dams and reservoirs. ## Water Cycle The water cycle is a continuous process where water moves around Earth through key stages. It includes three main processes: 1. **Evaporation:** Liquid water from rivers, lakes, and oceans turns into water vapor and rises into the atmosphere. 2. **Condensation:** Water vapor cools, forming clouds, fog, and mist. 3. **Precipitation:** Water in liquid or solid form (rain, snow, or hail) falls to Earth. Additionally, water flows and interacts with the environment through: - **Plant Uptake:** Plants absorb water from the soil. - **Transpiration:** Water evaporates from plant leaves. - **Runoff:** Water flows over the Earth's surface into rivers and lakes. - **Infiltration and Groundwater Flow:** Water seeps into the soil and moves through underground layers. ## Hydrological Cycle 1. **Evaporation** - Water evaporates from surface sources like rivers, lakes, and oceans, from soil, and through plant transpiration, converting liquid water into vapor. 2. **Condensation** - It is the process by which vapor is converted into solid form (Clouds) 3. **Precipitation** - Is any liquid or frozen water that forms in the atmosphere and falls back to the Earth. 4. **Infiltration** - After water reaches the ground it infiltrates into the ground. # Chapter 2: Precipitation ## Precipitation - It is the release of water from the atmosphere to reach the surface of the earth. ## Orographic Precipitation - It is an air mass being forced to rise over an obstruction like mountain range. ## Aggregation - The process when an ice particle grows by collision. ## Dry Air - It is all the gases in air except water vapor. ## Cold Clouds - This type of cloud occurs at high altitudes where temperature is less than -40°C, and are comprised exclusively of ice particles. ## Warm Clouds - A type of cloud that occur at lower altitudes where the temperature is greater than 0°C and are made up only cloud droplets. ## Hail - This type of precipitation starts as ice particles in the highest part of very large storm clouds. ## Dew - It is a type of precipitation were the water vapor condenses into liquid water. ## Static and Dynamic - the two influences on precipitation ## India - the earliest written reference to measuring rainfall dates from the 4th century BC. # Chapter 3: Evaporation ## Summer - a kind of weather that limits the water availability in evaporation process. ## hPa - Hectopascal ## Vapor Pressure Deficit - The difference between saturation and actual evaporation ## Evaporation Pans - The most common method for the measurement of evaporation. - It is a large pan of water with a measuring instrument that allows you to record how much water is lost over a time period. ## Thornthwaite - It is an accurate method for determining the evaporation rate at least 1 month or 30 days. ## Stomatal Resistance - Sometimes referred to as CANOPY RESISTANCE ## Actual Evaporation - It can be equal to Potential Evaporation (PE) under wet conditions but will be lower when water availability is limited. ## Transpiration - It is the release of water vapor from plant surfaces, primarily through stomata during photosynthesis. ## Mass Balance Estimation - This method requires accurate measurement of precipitation, runoff, and change in storage. ## Simplifications to Penman - This adaptation of the Penman equation is important for regional scale evapotranspiration assessment using satellite remote sensing. # Chapter 4: Interception and Surface Storage ## Interception - process where plants, leaves, and other vegetative surfaces catch and temporarily hold precipitation before it reaches the ground ## Throughfall - It can be held in the canopy until it is displaced by wind or drip off leaves, eventually falling to the ground ## Stemflow - it can rundown the stems of leaves and branches towards the trunk, and into the ground at the base of the trunk. ## Direct Throughfall - LAI the ratio of leaf area to ground surface area. The lesser the LAI, the higher the chance of a Direct Througfall. ## Rainfall Characteristics - Extensive rainfall or light showers. ## Interception Gain - refers to the idea that forests and their canopies can capture and retain additional moisture from sources like fog or low-lying clouds, which isn't counted as traditional rainfall but still contributes to the overall water budget in a region, having the occurrence of interception gain. ## Above-Canopy Precipitation - the rain, snow, or any other kind of water that falls from the sky and lands on the top of a forest or plant canopy ## Depression Storage - refers to small low points in undulating terrain that can store precipitation that otherwise would become runoff. The precipitation stored in these depressions is then either removed through infiltration into the ground or by evaporation ## Core Sampler - the simplest method of measuring of snow depth ## Satellite Remote Sensing - Main Method of estimation snow cover ## Microwave Data - Offers a far better method of detecting snow cover ## Ice - Is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. ## Snowmelt - It is the phase change of snowpack into liquid water ## Snow - Snow is precipitation that forms when water vapor freezes ## Snow pillow - A sealed plastic pillow normally filled with some form of anti-freeze and connected to a pressure transducer. ## Interception Estimation - The process of quantifying how much rainfall is stored and evaporated by above-ground structures, such as vegetation and surface litter ## Interception Loss - While water sits on the canopy, prior to indirect throughfall or stemflow, evaporation can occur. When this evaporation occurs, this is when interception loss happens ## Leaf Area Index - The ratio of leaf area to the ground surface ## Interception Measurement - The most common method of assessing the amount of canopy interception loss is to measure the precipitation above and below a canopy and assume the difference is from interception ## Water in Storage - It is actually a part of dynamic system consisting of an inflow, outflow and a movement of water between the two. # Chapter 5: Groundwater ## Groundwater - Water stored in the tiny pore spaces of soil, rock, sand, and gravel. ## Pressure Head - It means that groundwater can flow uphill rather than just downwards because of the elevation difference. It follows that if we are to understand the ability of groundwater to move, we need to consider both the pressure head and the elevation head. ## Elevation Head - This difference in height means gravity is working in your favour. ## Components of Bernoulli's Equation - Elevation Head, Pressure Head, Velocity Head ## Hydraulic Gradient - Being the difference in elevation between two points, divided by the distance between them. In other words, and applied in a groundwater context, the slope of the lines of hydraulic head. ## Darcy's Law - This factor is now known as the hydraulic conductivity, sometimes also referred to as the coefficient of permeability. ## Aquifer - A geological formation that can transmit and store significant amounts of water. ## Confined Aquifer - A confined aquifer is under pressure and surrounded by impermeable layers ## Unconfined Aquifer - an unconfined aquifer is open to atmospheric pressure. ## Aquitard - It transmits water at a slow rate, insufficient for significant water extraction. ## Aquifuge - Type of geological formations acts as a total barrier to groundwater flow. ## Recharge - process ensures the sustainability of an aquifer by replenishing groundwater levels ## Piezometer in Groundwater Management - To monitor groundwater pressure and flow direction. ## Effective Porosity - Sum of specific yield and specific retention ## Capillary Forces - It pertains to the types of forces which prevents some of the water [articles from being extracted. ## Transmissivity - The product of saturated hydraulic conductivity and thickness of aquifer. ## Storativity - the amount of water which can be removed from a unit volume of confined aquifer per unit decline in water level. ## Sand - type of aquifer is considered most useful due to its balanced specific yield and specific retention ## Saturated and Unsaturated Zones - following zones does groundwater primarily exist in ## Porosity - commonly used a symbol "n" ## Factors that influences porosity - The shape and size of the particles in soil or rock.