HYDROLOGY • • HYDROLOGIC LOSSES • • • • Collectively, that part of the rainfall that does not show up as a runoff. Also called abstractions. Infiltration, Evaporation, Transpiration, Interception. Occurs when water flows over the surface of the land. It happens when the ground is saturated, impermeable, or the rainfall rate exceeds the soil's infiltration capacity. Water moves across the land, entering streams, rivers, or lakes. THROUGHFLOW • • • Refers to the lateral movement of water within the soil. Occurs when infiltrated water moves through the unsaturated zone of the soil and flows downslope toward a water body. Water travels underground but near the surface, often feeding streams and rivers gradually. INTERCEPTION • • Is that portion of the rainfall that is intercepted by trees, plants, obstacles, and vegetation before it can reach the ground. Rainfall that drops through the vegetation is called throughfall. It is subsequently lost to the atmosphere through evaporation and transpiration. INFILTRATION INFILTRATION RATE • • • • • Plays a crucial role in hydrology and should be a key consideration in water resource management. Replenishes soil moisture, recharges aquifers and ultimately supports stream flows during dry periods. The process by which the water enters the soil from the ground surface, usually fast at the beginning and slow at later stages. Takes place at uppermost stratum of soil and movement is vertical. • • Refers to the infiltration per unit time; expressed in volume per unit area per unit time, or depth per unit time. Example: An infiltration rate of 5L per square meter per hour (It means that for every square meter of land, 5 liters of water is absorbed by the soil every hour). Example: An infiltration rate of 2cm per hour (Every hour, water is moving 2 cm deeper into the soil). CUMULATIVE INFILTRATION PERCOLATION • • • • When water enters the ground surface and travels through the soil to finally join the ground water reserves. Happens at a deeper depth when water move vertically to join water table. In between unsaturated zone and saturated zone of the soil. Usually, slow compared to infiltration. • • Refers to the summation of the depth of water absorbed by a soil in a specified elapsed time in reference to the time of initial water application. For example, if water was applied at the start of a rainstorm, and after 1 hour, the soil has absorbed 3 cm of water, and after 2 hours, it has absorbed a total of 6cm, the cumulative infiltration at the 2-hour mark would be 6cm. SEEPAGE IMPORTANCE OF INFILTRATION • • • • • • • • the process of seeping by which a liquid leek through a porous substance. Thus, water seepage occurs through a porous soil. Movement of water is not restricted to vertical direction only as in above two cases. Slowest among the three. When water enters the ground surface at the upstream side of a retaining structure like a dam and comes out at the downstream side. SURFACE RUNOFF Water conservation Reduced soil erosion by runoff Water reservoir design SOIL HORIZONS/LAYERS 1. 2. 3. 4. 5. Humus (O Horizon) - organic layer of soil made mostly of litter and decomposed organic matter A Horizon - where seeds germinate and plant roots grow B Horizon - contains clay and mineral deposits C Horizon - plant roots do not penetrate in this layer, very little organic material is found Bedrock - unweathered rocks • • Loam – best soil type Clay – worst soil type SOIL STRUCTURE FACTORS AFFECTING INFILTRATION INFILTRATION RATES • 1. WATER (fluid) Intensity of rainfall - if rain falls too heavily, it may exceed the infiltration rate, leading to runoff. ↑ Flow rate • Viscosity - refers to a fluid's resistance to flow, essentially measuring how thick or thin it is. ↑ Viscosity • • • • ↓ Infiltration Turbidity - a measure of how cloudy or murky water is due to the presence of suspended particles. Water carrying fine sediments can clog soil pores, reducing infiltration rates. ↑ Turbidity • • • ↓ Infiltration ↓ Infiltration 2. SOIL (medium) Soil texture, soil structure; The larger the pore size, the greater is the infiltration rate; Surface sealing or puddling of soil - formation of a thin compact layer on the surface as a result of severe breakdown of soil structure caused by the beating action of raindrops and flow of water over the surface Porosity: High porosity promotes infiltration as more spaces are available for water to fill. Porosity - porosity, moisture holding capacity, permeability Structure - the more stable the soil aggregates are, the higher is the soil capability to store and transmit water. SOIL CLASSIFICATION • USDA Soil Classification (United State Department of Agriculture) defines twelve major soil texture classifications based on factors like their physical properties, climate and biological activity. • • • • • 3. VEGETATION AND CULTURAL PRACTICES Vegetal cover protects the soil against raindrop energy and improves soil structure through production of organic matter and root penetration. Reduces surface sealing. Tillage practices loosen up the upper soil layer thereby increases the rate of surface entry and increases porosity of the plowed layer. 4. ANTECEDENT MOISTURE CONDITION Refers to the soil's moisture level before rainfall or irrigation. High antecedent moisture condition causes reduction in pore space and rate of water movement. o Dry Soil: Dry soil can initially absorb water faster because of available pore space. o • • • • • Wet Soil: Water infiltration slows when the soil is already saturated because there's little or no pore space left for water to enter. 5. TOPOGRAPHY Influences the characteristics of surface runoff and interflow. Slope speeds up overland flow and, hence, the depth and time of distribution of direct runoff and infiltration. 6. USE OF SOIL ADDITIVES Use of organic matter (compost)- improves soil structure and porosity, enhancing infiltration. Chemicals (Polymers and soil stabilizers) that improve the soil structure hence increase infiltration. Use of mulches - a layer of material spread on top of soil to protect it and improve the soil's health. Reduces evaporation and prevents soil compaction, indirectly aiding infiltration.