ABE 66 Land and Water Conservation Engineering PDF

ABE 66 Land and Water Conservation Engineering Indie G. Dapin Department of Agricultural and Biosystems Engineering College of Engineering Central Mindanao University  Sustainable Water Resources and...

ABE 66 Land and Water Conservation Engineering Indie G. Dapin Department of Agricultural and Biosystems Engineering College of Engineering Central Mindanao University  Sustainable Water Resources and Management Sources of water Water resources assessment/characterization Water resources development  Sustainable Water Resources and Management ▪ involves the development and use of water resources in a way that meets current needs without compromising the ability of future generations to meet their own needs. ▪ Balances the demands of agriculture, industry, domestic use, and environmental conservation. Soil and Water Conservation Engineering 7th Edition  Principles of Sustainability ▪ Equity ▪ Efficiency ▪ Environmental Protection Soil and Water Conservation Engineering 7th Edition Question Does the amount of water on Earth increase or decrease over time?  General types of water source 1. Groundwater 2. Surface water 3. Rainwater https://www.open.edu/openlearncreate/mod/oucontent/view.php?id=79999&printable=1  Groundwater About 97% of all available fresh water is groundwater. Groundwater supplies are less seasonal than surface waters. Aquifers act as underground reservoirs whose storage capacity attenuates the variability of precipitation. Groundwater levels fluctuate, however, and can drop significantly in drought periods. Where groundwater drops below a pump intake, one might deepen the well and/or lower the pump or intake. Soil and Water Conservation Engineering 7th Edition  Groundwater can be found almost anywhere, is highly variable in terms of ease of access, quantity, and quality. The potential yield of a well depends on the characteristics of the aquifer: porosity, hydraulic conductivity of the primary matrix, fracturing, and thickness of the water-bearing strata. Groundwater quality problems: extreme hardness, dissolved salts, iron, etc. Soil and Water Conservation Engineering 7th Edition  Groundwater Terminologies unsaturated zone – (also called vadose zone) zone not completely saturated, i.e., the void spaces in the soil and rock (porous media) are not completely filled with water. saturated zone – zone below vadose zone, there voids are filled completely with water. zone of rock fracture – combined zone for unsaturated and saturated zones, where rock formations fracture in response to stresses from deformations of the earth’s crust (folding and faulting). zone of rock flowage - zone below saturated zone where the rock is under such pressure that it deforms plastically. Although water exists in the rock at such depths, it is unavailable for use. Classification of near-surface zones of the earth's crust and Soil and Water Conservation Engineering 7th Edition underground waters (all water below earth’s surface)  Groundwater Terminologies Water table – (also called a phreatic surface) is the upper surface of a saturated zone. If a hole were bored into the earth (e.g., a well), water would enter that hole to the level of the water table. At the water table, the pressure in the underground water is equal to atmospheric pressure. Capillary fringe – a zone, located just above the water table, where the porous media is virtually saturated. Its depth ranges from a few millimeters in coarse sands to 2-3 m in clays. Because water wets almost all media, the surfaces of the solids are covered by a film of water. Water in the capillary fringe is not readily extractable. It can be an important consideration in the design of drainage systems but is generally ignored in groundwater development. Classification of near-surface zones of the earth's crust and Soil and Water Conservation Engineering 7th Edition underground waters (all water below earth’s surface)  Groundwater Terminologies Perched waters – this is formed due to the ponding of water (localized saturated zone) above a restrictive layer (less permeable material like clay, an unsaturated media) (also called a phreatic surface) is the upper surface of a saturated zone. If a hole were bored into the earth (e.g., a well), water would enter that hole to the level of the water table. At the water table, the pressure in the underground water is equal to atmospheric pressure. Classification of near-surface zones of the earth's crust and Soil and Water Conservation Engineering 7th Edition underground waters (all water below earth’s surface) Types of Porous media (Void or pores spaces) (a) well sorted sand (b) poorly sorted sand; (c) well sorted sand with precipitates that reduce porosity (section view); (d) rock with fractures; (e) rock with dissolution channels. Primary porosity – void space between particles Secondary porosity – voids or void systems that are much larger than the primary particles. Soil and Water Conservation Engineering 7th Edition  Groundwater Terminologies AQUIFER – the hydrogeologic formation that is capable of storing and transmitting groundwater at sufficient quantities. A saturated stratum of relatively high permeability AQUIFUGE – a formation that can neither store nor transmit groundwater. AQUITARD – a special formation that can store groundwater but can only transmit it at slow rates. A relatively impermeable layer that restricts vertical flow. An aquifer is NOT an AQUICLUDE – a formation that contains underground lake or groundwater but is not capable of river. transmitting it as sufficient quantities. More restrictive than aquitard. Soil and Water Conservation Engineering 7th Edition  Aquifer structure in gently sloping sedimentary systems Major types of aquifer Unconfined aquifer – has no aquitard above it, so water percolating from the land surface can freely join the saturated zone. Confined aquifer – a formation that has an aquitard as its upper boundary. It acts as huge flattened pipes conducting water laterally from recharge areas to eventual discharge areas that may be many kilometers distant Soil and Water Conservation Engineering 7th Edition  Aquifer structure in gently sloping sedimentary systems Artesian wells– occurs in a well bored into confined aquifers. The water will rise above towards the hydraulic head level (potentiometric surface or piezometric surface). Flowing artesian wells– are artesian wells flowing above the land surface. This occur where a well in a discharge area taps water at a higher potential than the ground surface. The top of the well is below the potentiometric surface. Soil and Water Conservation Engineering 7th Edition  Properties of an Aquifer Hydraulic Conductivity (k) – flow rate per unit are normal to the flow direction resulting from one unit of hydraulic gradient causing the flow. Transmissivity or Transmissibility (T) – ability to transmit water throughout its entire saturated thickness (b). Expressed as 𝑇 = 𝑘𝑏. Storage coefficient or storativity –volume of water that can be stored in or released from an aquifer per unit horizontal area per unit change in hydraulic head Specific storage (Ss) –change in storage(Sc) in an aquifer per unit decline in head (b). Soil and Water Conservation Engineering 7th Edition  Properties of an Aquifer Specific yield (Sy) – volume of water release from storage in an unconfined aquifer per unit horizontal area per unit decline in water table. Specific retention (Sr) – volume of water that remains within the porous portion of the aquifer after releasing the stored volume represented by specific yield. effective porosity (n) – 𝑛 = 𝑆𝑦 + 𝑆𝑟 Soil and Water Conservation Engineering 7th Edition  Aquifer classification for based on the hydraulic conductivity for well development: 1. ≥ 10−5 m/s = good aquifer 2. 10−9 – 10−5 m/s = poor aquifer 3. < 10−9 = insufficient water, not recommended for development It consist of sand, gravel or rock saturated with water that act like a SPONGE. GOOD AQUIFERS = high permeability and porosity  Well Hydraulics Steady-state well discharge for unconfined aquifer (For a well that fully penetrates an extensive, unconfined aquifer) 𝜋𝐾 ℎ2 2 − ℎ1 2 𝑞= log 𝑒 𝑟2 Τ𝑟1 𝑞 = discharge (𝑙 3 /𝑡) 𝑘 = hydraulic conductivity (𝑙/𝑡) 𝑟2 , 𝑟1 = radial distances from the center of the well (l) ℎ2 , 𝑟1 = height of the water level at 𝑟2 , 𝑟1 above the bottom of the aquifer (l) Cross section of a well in a homogenous, unconfined aquifer Soil and Water Conservation Engineering 7th Edition  Well Hydraulics Steady-state well discharge for confined aquifer (For a well that fully penetrates an extensive, confined aquifer) 2𝜋𝐾𝑑 ℎ2 − ℎ1 𝑞= log 𝑒 𝑟2 Τ𝑟1 𝑞 = discharge (𝑙 3 /𝑡) 𝑑 = thickness of the confined aquifer (l) 𝑘 = hydraulic conductivity (𝑙/𝑡) 𝑟2 , 𝑟1 = radial distances from the center of the well (l) ℎ2 , 𝑟1 = height of the potentiometric surface at 𝑟2 , 𝑟1 above the bottom of the aquifer (l) Cross section of a well in a homogenous, confined aquifer Soil and Water Conservation Engineering 7th Edition  Well Hydraulics Radius of influence (For a well that fully penetrates an extensive, confined aquifer) 2𝜋𝐾𝑑 ℎ2 − ℎ1 𝑞= log 𝑒 𝑟2 Τ𝑟1 𝑞 = discharge (𝑙 3 /𝑡) 𝑑 = thickness of the confined aquifer (l) 𝑘 = hydraulic conductivity (𝑙/𝑡) 𝑟2 , 𝑟1 = radial distances from the center of the well (l) ℎ2 , 𝑟1 = height of the potentiometric surface at 𝑟2 , 𝑟1 above the bottom of the aquifer (l) Cross section of a well in a homogenous, confined aquifer Soil and Water Conservation Engineering 7th Edition  Well Hydraulics Approximate Characteristics of Various Natural Porous Media Soil and Water Conservation Engineering 7th Edition  Well Hydraulics Radius of influence The Siechardt formula - an empirical formula to estimate the radius of influence 𝑅 = 3000𝑆𝑊 𝐾 1Τ2 𝑅 = Radius of influence, in m 𝑆𝑊 = drawdown in the well, in m 𝑘 = hydraulic conductivity of the aquifer medium (𝑚/𝑠) Soil and Water Conservation Engineering 7th Edition  CONE OF DEPRESSION Cone of depression happens when pumping rate is greater than the groundwater recharge. Sample Problem 1. Estimate the discharge from a 0.3-m diameter well fully penetrating a confined aquifer given: aquifer thickness 26 m height of static potentiometric surface above the top of the aquifer 85 m drawdown at 20-m radius 35 m drawdown at 100-m radius 5 m aquifer medium mixed sand hydraulic conductivity = 2 × 10−5 m/s 2. Estimate the hydraulic conductivity of an unconfined aquifer from the following pump test data: depth to restrictive layer 21 m depth to static water table 4 m drawdown at 10-m radius 8 m drawdown at 50-m radius 1.2 m well discharge 6 L/s Soil and Water Conservation Engineering 7th Edition Note: Results of the equations must be evaluated critically. If the drawdown in an unconfined system approaches the thickness of the aquifer, the calculated yield is not likely to be valid. For a confined aquifer, if the drawdown is so great that the cone of depression penetrates the top of the aquifer itself, the aquifer will begin to dewater, i.e., the upper part of the aquifer near the well will become unsaturated, altering the hydraulic behavior. The well will still produce, but the flow analysis is much more complicated. Steady-state conditions in the aquifers can never found in nature, the approximation is good for relatively short-term pumping. Where a well will be pumped for extended periods, e.g., for irrigation or municipal supplies, pumping tests should be run for as much as 30 days to evaluate the capacity of a well. The equations also assume that the wells fully penetrate the aquifers. If the well is screened in only part of the aquifer, there will be a vertical component added to the flow field, requiring a more complex analysis Soil and Water Conservation Engineering 7th Edition Assignment Enumerate and discuss other major large-scale dams in the Philippines. Discuss in terms of location, date of construction (start to finish), storage capacity, purpose, make, watershed area, services provided and other details.