BCE 313 Hydrology Self-Instructional Manual PDF

UNIVERSITY OF MINDANAO College of Engineering Education Civil Engineering Program Physically Distanced but Academically Engaged Self-Instructional Manual (SIM) for Self-Directed Learning (SDL) Co...

UNIVERSITY OF MINDANAO College of Engineering Education Civil Engineering Program Physically Distanced but Academically Engaged Self-Instructional Manual (SIM) for Self-Directed Learning (SDL) Course/Subject: BCE 313: HYDROLOGY SIM AUTHOR: Engr. DANIELYN F. PLAZOS Name of Teacher: Engr. MARIE FE Y. LACSADO THIS SIM/SDL MANUAL IS A DRAFT VERSION ONLY; NOT FOR REPRODUCTION AND DISTRIBUTION OUTSIDE OF ITS INTENDED USE. THIS IS INTENDED ONLY FOR THE USE OF THE STUDENTS WHO ARE OFFICIALLY ENROLLED IN THE COURSE/SUBJECT. EXPECT REVISIONS OF THE MANUAL.  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Table of Contents COURSE OUTLINE: BCE 313 - HYDROLOGY................................................................................................. 6 COURSE OUTLINE POLICY..................................................................................................................................... 6 Course Information..................................................................................................................................................... 9 BIG PICTURE IN FOCUS: ULO-1.......................................................................................................................... 9 Metalanguage................................................................................................................................................................ 9 Essential Knowledge............................................................................................................................................... 10 HYDROLOGIC CYCLE............................................................................................................................................... 10 THE IMPACT OF HYDROLOGIC CYCLE IN HUMAN LIFE.......................................................................... 11 COMPOSITION OF ATMOSPHERE...................................................................................................................... 11 NUCLEATION AND PARTICLE GROWTH........................................................................................................ 11 HOW CLOUDS ARE FORMED?............................................................................................................................. 12 WHY CLOUDS HAVE DIFFERENT COLORS?................................................................................................... 12 TYPES OF CLOUDS.................................................................................................................................................... 12 WATERSHED AND ITS PARTS............................................................................................................................. 13 INSTRUMENTS IN MEASURING PRECIPITATION....................................................................................... 14 DIMENSION OF RAIN GAUGE.............................................................................................................................. 15 SET-UP FOR RAIN GAUGE..................................................................................................................................... 15 ESTIMATING THE MISSING DATA AND ADJUSTMENT OF RECORDS................................................ 16 MEAN AREAL PRECIPITATION........................................................................................................................... 19 DEPTH-AREA-DURATION ANALYSIS............................................................................................................... 22 GRAPHICAL REPRESENTATION OF RAINFALL........................................................................................... 23 Self-Help:...................................................................................................................................................................... 24 Let’s Check................................................................................................................................................................... 25 In a Nutshell................................................................................................................................................................ 28 COURSE SCHEDULE:.................................................................................... 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BIG PICTURE IN FOCUS: ULO-2A.................................................................................................................... 29 Metalanguage............................................................................................................................................................. 29 Essential Knowledge............................................................................................................................................... 29 WATER LOSSES......................................................................................................................................................... 29 EVAPORATION........................................................................................................................................................... 29 METHOD IN ESTIMATING EVAPORATION.................................................................................................... 30 INSTRUMENTS USED IN MEASURING EVAPORATION............................................................................. 31 TRANSPIRATION...................................................................................................................................................... 31 EVAPOTRANSPIRATION........................................................................................................................................ 32 Page 2 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 FACTORS AFFECTING EVAPOTRANSPIRATION.......................................................................................... 34 PAN COEFFICIENT................................................................................................................................................... 34 MEASURES TO REDUCE LAKE EVAPORATION............................................................................................ 35 SOIL EVAPORATION................................................................................................................................................ 36 INTERCEPTION.......................................................................................................................................................... 37 DEPRESSION STORAGE.......................................................................................................................................... 38 Self-Help:...................................................................................................................................................................... 38 Let’s Check................................................................................................................................................................... 39 Let’s Analyze............................................................................................................................................................... 39 BIG PICTURE IN FOCUS: ULO-2B.................................................................................................................... 40 Metalanguage............................................................................................................................................................. 40 Essential Knowledge............................................................................................................................................... 41 RUNOFF PHENOMENON........................................................................................................................................ 41 TIME OF CONCENTRATION................................................................................................................................. 42 RUNOFF CALCULATIONS...................................................................................................................................... 45 STREAMS...................................................................................................................................................................... 49 STREAM CLASSIFICATION.................................................................................................................................... 49 FLOOD PREDICTION................................................................................................................................................ 50 Self-Help:...................................................................................................................................................................... 51 Let’s Check................................................................................................................................................................... 51 Let’s Analyze............................................................................................................................................................... 51 COURSE SCHEDULE..................................................................................... 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BIG PICTURE IN FOCUS: ULO-3A.................................................................................................................... 54 Metalanguage............................................................................................................................................................. 54 Essential Knowledge............................................................................................................................................... 54 HYDROGRAPH............................................................................................................................................................ 54 TYPES OF HYDROGRAPH...................................................................................................................................... 56 UNIT HYDROGRAPH FROM COMPLEX STORMS.......................................................................................... 61 Big Picture in Focus: ULO-3b............................................................................................................................... 66 Metalanguage............................................................................................................................................................. 66 Essential Knowledge............................................................................................................................................... 66 INFILTRATION AND PERCOLATION................................................................................................................ 66 METHODS OF DETERMINING INFILTRATION............................................................................................. 66 INFILTRATION RATE.............................................................................................................................................. 68 INFILTRATION INDICES........................................................................................................................................ 69 SUPRA RAIN TECHNIQUE..................................................................................................................................... 70 GREEN AND AMPT INFILTRATION METHOD............................................................................................... 71 Page 3 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 INTERPRETING GREEN AND AMPT GRAPH AND RESULTS................................................................... 73 PERCOLATION........................................................................................................................................................... 74 DIFFERENCE BETWEEN INFILTRATION AND PERCOLATION............................................................. 76 Self-Help:...................................................................................................................................................................... 77 LET’S ANALYZE......................................................................................................................................................... 77 IN A NUTSHELL......................................................................................................................................................... 78 BIG PICTURE IN FOCUS: ULO-3C..................................................................................................................... 79 Metalanguage............................................................................................................................................................. 79 Essential Knowledge............................................................................................................................................... 79 GROUNDWATER....................................................................................................................................................... 79 CONFINED AND UNCONFINED AQUIFERS.................................................................................................... 80 DARCY’S LAW............................................................................................................................................................. 82 HYDRAULIC OF WELLS.......................................................................................................................................... 82 SPECIFIC CAPACITY................................................................................................................................................. 84 CAVITY WELLS.......................................................................................................................................................... 84 GROUNDWATER PROBLEMS............................................................................................................................... 86 Self-Help:...................................................................................................................................................................... 87 Let’s Check................................................................................................................................................................... 87 Let’s Analyze............................................................................................................................................................... 87 BIG PICTURE IN FOCUS: ULO-3D.................................................................................................................... 88 Metalanguage............................................................................................................................................................. 88 Essential Knowledge............................................................................................................................................... 89 BASIC PROBABILITY............................................................................................................................................... 89 RETURN PERIOD....................................................................................................................................................... 91 DESIGN STORMS....................................................................................................................................................... 92 REGRESSION ANALYSIS......................................................................................................................................... 92 STANDARD ERROR OF ESTIMATE.................................................................................................................... 94 Self-Help:...................................................................................................................................................................... 95 LET’S ANALYZE......................................................................................................................................................... 96 IN A NUTSHELL......................................................................................................................................................... 97 COURSE SCHEDULE..................................................................................... 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BIG PICTURE IN FOCUS: ULO-4A.................................................................................................................... 98 Metalanguage............................................................................................................................................................. 98 Essential Knowledge............................................................................................................................................... 98 RESERVOIR ROUTING............................................................................................................................................. 98 STREAMFLOW ROUTING.................................................................................................................................... 105 Self-Help:.................................................................................................................................................................... 110 Page 4 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Let’s Check................................................................................................................................................................. 110 Let’s Analyze............................................................................................................................................................. 110 IN A NUTSHELL....................................................................................................................................................... 113 BIG PICTURE IN FOCUS: ULO-4B.................................................................................................................. 114 Metalanguage........................................................................................................................................................... 114 Essential Knowledge............................................................................................................................................. 114 SIZE OF FLOODS...................................................................................................................................................... 115 ESTIMATION OF PEAK FLOOD.......................................................................................................................... 116 METHODS OF FLOOD CONTROL...................................................................................................................... 117 FLOOD CONTROL BY RESERVOIRS................................................................................................................. 117 RETARDING BASINS.............................................................................................................................................. 118 CONSTRUCTION OF LEEVES.............................................................................................................................. 119 CHANNEL IMPROVEMENT................................................................................................................................. 119 SOIL CONSERVATION MEASURES................................................................................................................... 123 FLOOD CONTROL ECONOMICS......................................................................................................................... 125 COMBINATION OF FLOOD CONTROL MEASURES.................................................................................... 127 FLOOD FORECASTING AND WARNING......................................................................................................... 127 Self-Help:.................................................................................................................................................................... 129 LET’S CHECK............................................................................................................................................................. 129 LET’S ANALYZE....................................................................................................................................................... 129 IN A NUTSHELL....................................................................................................................................................... 130 BIG PICTURE IN FOCUS: ULO-4C................................................................................................................... 131 Metalanguage........................................................................................................................................................... 131 Essential Knowledge............................................................................................................................................. 131 ROLE IN HYDROLOGY IN WATER RESOURCES PLANNING AND MANAGEMENT...................... 132 AGENCIES THAT ARE INVOLVED IN COLLECTING HYDROLOGIC DATA........................................ 133 STATUS OF WATER RESOURCES IN THE PHILIPPINES......................................................................... 134 CLASSIFICATION OF BODIES OF WATER IN THE PHILIPPINES......................................................... 134 Self-Help:.................................................................................................................................................................... 136 LET’S CHECK............................................................................................................................................................. 136 IN A NUTSHELL....................................................................................................................................................... 136 COURSE SCHEDULE..................................................................................... Error! Bookmark not defined. Page 5 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Course Outline: BCE 313 - Hydrology Course Coordinator: Marie Fe Y. Lacsado Email: [email protected] Student Consultation: By appointment Mobile: 09228931053 Phone: (082) 296-1084 or 300-5456 loc. 133 Effectivity Date: May 2020 Mode of Delivery: Blended (On-line with face to face or virtual sessions) Time Frame: 54 hours Student Workload: Expected Self-Directed Learning Pre-requisite: BCE 221 Co-requisite: BCE 314/L Credit: 3.0 units lecture Attendance Requirements: A minimum of 95% attendance is required at all scheduled Virtual or face-to-face sessions Course Outline Policy Areas of Concern Details Contact and Non-contact Hours This 3-unit course self-instructional manual is designed for blended learning mode of instructional delivery with scheduled face to face or virtual sessions. The expected number of hours will be 108 including the face-to-face or virtual sessions. The face-to-face sessions shall include the summative assessment tasks (exams) since this course is crucial in the licensure examination for civil engineers. Assessment Task Submission Submission of assessment tasks shall be on 3rd, 5th, 7th and 9th week of the term. The assessment paper shall be attached with a cover page indicating the title of the assessment task (if the task is performance), the name of the course coordinator, date of submission and name of the student. The document should be emailed to the course coordinator. It is also expected that you already paid your tuition and other fees before the submission of the assessment task. If the assessment task is done in real time through the features in the Blackboard Learning Management System, the schedule shall be arranged ahead of time by the course coordinator.. Turnitin Submission To ensure honesty and authenticity, all assessment (if necessary) tasks are required to be submitted through Turnitin with a maximum similarity index of 30% allowed. This Page 6 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 means that if your paper goes beyond 30%, the students will either opt to redo her/his paper or explain in writing addressed to the course coordinator the reasons for the similarity. In addition, if the paper has reached more than 30% similarity index, the student may be called for a disciplinary action in accordance with the University’s OPM on Intellectual and Academic Honesty. Please note that academic dishonesty such as cheating and commissioning other students or people to complete the task for you have severe punishments (reprimand, warning, expulsion). Penalties for Late The score for an assessment item submitted after the Assignments/Assessments designated time on the due date, without an approved extension of time, will be reduced by 5% of the possible maximum score for that assessment item for each day or part day that the assessment item is late. However, if the late submission of assessment paper has a valid reason, a letter of explanation should be submitted and approved by the course coordinator. If necessary, you will also be required to present/attach evidences. Return of Assignments/ Assessment tasks will be returned to you two (2) Assessments weeks after the submission. This will be returned by email or via Blackboard portal. For group assessment tasks, the course coordinator will require some or few of the students for online or virtual sessions to ask clarificatory questions to validate the originality of the assessment task submitted and to ensure that all the group members are involved. Assignment Resubmission You should request in writing addressed to the course coordinator his/her intention to resubmit an assessment task. The resubmission is premised on the student’s failure to comply with the similarity index and other reasonable grounds such as academic literacy standards or other reasonable circumstances e.g. illness, accidents financial constraints. Re-marking of Assessment You should request in writing addressed to the Papers and Appeal program coordinator your intention to appeal or contest the score given to an assessment task. The letter should explicitly explain the reasons/points to contest the grade. The program coordinator shall communicate with the students on the approval and disapproval of the request. Page 7 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 If disapproved by the course coordinator, you can elevate your case to the program head or the dean with the original letter of request. The final decision will come from the dean of the college. Grading System All culled from BlackBoard sessions and traditional contact Course discussions/exercises – 30% 1st formative assessment – 10% 2nd formative assessment – 10% 3rd formative assessment – 10% All culled from on-campus/onsite sessions (TBA): Final exam – 40% Submission of the final grades shall follow the usual University system and procedures. Preferred Referencing Style Depends on the discipline; if uncertain or inadequate, use the general practice of the APA 6th Edition. Student Communication You are required to create a umindanao email account which is a requirement to access the BlackBoard portal. Then, the course coordinator shall enroll the students to have access to the materials and resources of the course. All communication formats: chat, submission of assessment tasks, requests etc. shall be through the portal and other university recognized platforms. You can also meet the course coordinator in person through the scheduled face to face sessions to raise your issues and concerns. For students who have not created their student email, please contact the course coordinator or program head. Contact Details of the Dean Dr. Charlito L. Cañesares Email: [email protected] Phone: (082) 296-1084 or 300-5456 loc. 133 Contact Details of the Program Engr. Showna Lee T. Sales Head Email: [email protected] Phone: (082) 296-1084 or 300-5456 loc. 133 Students with Special Needs Students with special needs shall communicate with the course coordinator about the nature of his or her special needs. Depending on the nature of the need, the course coordinator with the approval of the program coordinator may provide alternative assessment tasks or extension of the deadline of submission of assessment tasks. However, the alternative assessment tasks should still be in the service of achieving the desired course learning outcomes. Help Desk Contact Frida Santa O. Dagatan Page 8 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 [email protected] 09562082442 082-2272902 Library Contact Brigida E. Bacani [email protected] 09513766681 Course Information- see/download course syllabus in the BlackBoard LMS CC’s Voice: Hello future engineer! Welcome to this course BCE 313: Hydrology. By now, I am confident that you really wanted to become a civil engineer and that you have foreseen yourself building and exploring the world. CO: Upon completion of the course, you are expected to: CO 1: Develop a good understanding of processes which water cycle between the bodies of water, atmosphere, and land surface and of the physical meaning of hydrologic models which capture/stimulate selected hydrologic phenomena. CO 2: Make intelligent decisions on problems that involve hydrologic analysis and design with social and moral consideration. Let us begin! Big Picture Week 1-3: Unit Learning Outcomes-Unit 1 (ULO-1): At the end of the unit, you are expected to a. Describe the phases of hydrologic cycle and relation to meteorology and its impact to human life with the corresponding application. Big Picture in Focus: ULO-1. Describe the phases of hydrologic cycle and relation to meteorology and its impact to human life with the corresponding application. Metalanguage The most essential terms below are defined for you to have a better understanding of this section in the course. 1. Hydrology. The scientific study of the properties, distribution, and effects of water on the earth’s surface, in soil and underlying rocks, and in the atmosphere. 2. Hydraulics. Involving movement operated by a fluid under pressure. It deals with the application of fluid mechanics to engineering devices involving fluids, usually water or oil. Page 9 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 3. Hydrologic Cycle. Circulation or cycle that controls the distribution of Earth’s water as it evaporates from bodies of water, condenses, precipitates and returns to those bodies of water 4. Watershed. A ridge of high land dividing two areas that are drained by different river systems. The region draining into the river, river system, or other bodies of water. It is also called drainage basin. 5. Meteorology. Is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. 6. Humidity. Is the amount of water vapor in the air. Essential Knowledge We must know the different process and its role in hydrologic cycle because it is the foundation in this course and connected to the other topics like meteorology and watershed. Also, we must identify the importance or the impact of the hydrologic cycle in the daily life. HYDROLOGIC CYCLE 1. Precipitation – is any type of water that forms in the Earth’s atmosphere and then drops onto the surface of the Earth. 2. Condensation – The process by which the water vapor changes to a liquid. 3. Evaporation – Water that comes from the river, seas, etc. transfer into a gas or water vapor. 4. Runoff – Flow of water that is not absorbed into the soil. The overflow from the surface to the bodies of water like river. 5. Transpiration – Is the process by which plants and animals including human gives off water vapor through pores and evaporate it. 6. Interception - When rain falls on the earth's surface, some of it strikes vegetation, buildings, and other objects. This rain is said to be intercepted. 7. Infiltration- Rain falls into the ground infiltrates from the surface up to the root zone. 8. Percolation- From root zone, water will move down till reach to the aquifer. 9. Groundwater- is beneath most places on the land surface. This water is contained in the voids within the underlying geologic material, and the water-bearing formations are called aquifers. Figure 1: Hydrological Cycle (Source: britannica.com) Page 10 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 THE IMPACT OF HYDROLOGIC CYCLE IN HUMAN LIFE Hydrologic cycle is connected to the human life. Without water, human and other living things will vanish. Also, water is also part in the activities in daily life like irrigation, hydroelectric power plant, groundwater source, Recreational activities and source of food. That’s why, hydrologic cycle is important and has a great impact in human life. COMPOSITION OF ATMOSPHERE Atmosphere is spheroidal envelope of gas and vapor surrounding a planet, retained by gravity. The composition of the earth’s atmosphere and most of its physical properties vary with altitude. Troposphere- Is the part that we live in. The lowest zone or part of the atmosphere. It extends from the earth’s surface to an altitude of about 5 miles (8km) at the poles and 10 miles (16km) at the equator. It characterized by decreasing temperature with increasing altitude. Also, it contains most of our weather, clouds, rain, snow. Stratosphere- This extends upwards from the tropopause to about 50 km. It contains so much ozone in the atmosphere. The increase in temperature with height occurs because of absorption of ultraviolet radiation (UVR) from the sun by this ozone. Temperatures in the stratosphere are highest over the summer pole and lowest over the winter pole. Mesosphere- The region above the stratosphere is called the mesosphere. The temperature again decreases with height reaching a minimum of about -90 degrees Celsius at the mesopause. Thermosphere- lies above the mesopause and is a region in which temperature again increase with height. This temperature is caused by the absorption of energetic ultraviolet and X-Ray radiation from the sun. Exosphere- Lies above 500km from the surface. It contains mainly oxygen and hydrogen atoms, but there are so few of them that they rarely collide- they follow “ballistic” trajectories under the influence of gravity, and some of them escape right out into space. Figure 2: Parts of the Atmosphere (Source: vtaide.com) NUCLEATION AND PARTICLE GROWTH Nucleation is the first step in the formation of either a new thermodynamic phase or a new structure via self-assembly or self-organization. Nucleation is typically defined to be the process that determines how long an observer has to wait before the new phase or self- Page 11 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 organized structure appears. For example, if a volume of water is cooled (at atmospheric pressure) below 0 degrees Celsius, it will tend to freeze into ice, but volumes of water cooled only a few degrees below 0 degrees Celsius often stay completely free of ice for long periods. At these conditions, nucleation of ice is either slow or does not occur at all. Nucleation is commonly how first-order phase transitions start, and then it is the start of the process of forming a new thermodynamic phase. In contrast, new phases at continuous phase transitions start to form immediately. Particle growth is the next process after nucleation. It is the temperature in the vicinity of the evaporation source is high to obtain the reasonable vapor pressure of the evaporant. As the evaporant moves away from the source, the temperature decreases, causing supersaturation of the vaporized material leading to the homogenous nucleation in the gas phase. At high supersaturation, a large amount of small particles is formed upon rapid nucleation in the gas phase. HOW CLOUDS ARE FORMED? Clouds form when moist, warm rising air cools and expands in the atmosphere. The vapor in the air condenses to form tiny droplets in which are the basis of clouds. WHY CLOUDS HAVE DIFFERENT COLORS? The different colors of the clouds are depending on the light of the sun. The clouds having dark color because the light of the sun cannot pass throughout the clouds. You can observe that in the night, the clouds have dark color because there is no light or enough light. The white clouds like cotton we see is that the light is evenly distributed in the clouds until the bottom of it. TYPES OF CLOUDS A cloud is a visible accumulation of a minute droplets of water, ice crystals or both, suspended in the air. Though they vary in shape and size, all clouds are basically formed in the same way through the vertical of air above the condensation level. Clouds may also form in contact with the ground surface, too. Such a cloud would be known as fog, ice fog, or mist. It is divided into three types: High-Level Clouds, Mid-Level Clouds, Low-Level Clouds. High-Level Clouds are composed of cirrocumulus, cirrus and cirrostratus. It has an altitude of 5km to 13 km from the earth’s surface. Cirrus – is one of the most common types of clouds that can be seen at any time of the year. They are thin and wispy with a silky sheen appearance. Cirrocumulus – among the most gorgeous out there. These usually form at about 5 km above the surface with small white fluff patterns that spread out for miles and miles over the sky. They are sometimes called “Mackerel Skies” because they can sometimes have a grayish color which makes the clouds look a bit like fish scales. Cirrostratus- have a sheet-like appearance that can look like a curly blanket covering the sky. They are quite translucent which makes it easy for the sun or the moon to peer through. Their color varies from the light gray to white and the fibrous bands can vary widely in thickness. Purely white cirrostratus clouds signify these have stored moisture, indicating the presence of a warm frontal system. Mid-Level Clouds are composed of altocumulus, altostratus and nimbostratus. It has an altitude of 2km up to 7km from the earth’s surface. Altocumulus- form at a lower altitude so they’re largely made of water droplets though they may retain ice crystals when forming higher up. Page 12 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Altostratus- often spread over thousands of square miles and are strongly linked to light rain or snow. Though they’re not capable of yielding heavy rain it’s common for altostratus clouds to morph into nimbostratus clouds which are packed with moisture and can deliver a pounding. Nimbostratus- form as a result of the gradual accumulation of moist area over a large area as the warm and moist area higher up in the atmosphere where it condenses. Low-Level Clouds are composed of stratus, cumulus, cumulonimbus, and stratocumulus. It has an altitude of 0km up to 2km from the earth’s surface. Stratus – composed of thin layers of clouds covering a large area of the sky. This is simply mist or fog when it forms close to the ground. Cumulus – It is the most recognizable out of all types of clouds. These adorable piles of cotton form a large mass with a well-defined rounded edge, which explains the name “cumulus” which is Latin word for “heap”. Cumulonimbus – is fluffy and white like cumulus but the cloud formations are far larger. It is a vertical developing type of cloud whose base grows from one up to eight kilometers, hence it’s commonly called a tower cloud. The rain comes and goes with this cloud but when it does, it can come pouring. When you see a cumulonimbus, you know there’s a thunderstorm waiting to happen somewhere. Stratocumulus – looks like a thick white blanket of stretched out cotton. They resemble cumulus clouds except they’re far bigger. The base is well-defined and flat but the upper part of the cloud is ragged due to convection with the cloud itself. Depending on the thickness of the cloud, a stratocumulus will have light to dark gray hues. Figure 3: Types of Clouds (Source: zmescience.com) WATERSHED AND ITS PARTS Watershed are composed of many parts including surface water (estuary, bay, river, creeks, streams, and wetlands), riparian areas, uplands and groundwater. Wetlands are an area of land that is saturated with water for all or part of the year. A wetland can be a marsh, pond, or bog. Wetlands are typically surrounded by riparian vegetation. They are like giant sponges that store water collected during wet periods, reduce flooding, filter out pollutants, diseases and nutrients, and slowly release the water into groundwater and/or Page 13 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 rivers, streams, and creeks during drier periods. In addition, wetlands provide habitat for wildlife and healthy wetlands naturally attract wildlife. Riparian Vegetation are the plants that grow along or near the riverbanks, lakes, and wetlands. The roots of riparian plants stabilize stream banks, and prevent erosion and silting-in of streams and river channels. Spongy soils in riparian areas slow and store water, reducing flooding and later releasing water to aquifers and streams. Uplands are areas where there is not usually standing water and would typically be either forested or agricultural land. Groundwater is all water under the surface of the ground. It is stored in the soil and it can be found far under the ground in deep aquifers or very near the ground surface. Groundwater flows through the soils into our streams, river, estuary and wetlands. It also rises to the surface in springs. Figure 4: Watershed and its Parts (Source: howstuffworks.com) INSTRUMENTS IN MEASURING PRECIPITATION Today, scientists can measure precipitation directly using ground-based instruments such as rain gauges or indirectly using remote sensing techniques like radar systems, aircraft, and Earth observing satellites. Rain Gauges measure precipitation amounts at a given location. Oftentimes, measurements from an individual rain gauge are used to represent precipitation conditions across larger areas. However, that isn’t always the best assumption. The reality is that precipitation may fall more or less-intensely at the location of the gauge or it may miss the gauge entirely. Damage or obstructions to a gauge or the presence of strong winds can also introduce error. Ground-based weather radars emerged during World War II and have since been used to observe precipitation, mostly over land. It send out pulses of microwave energy in narrow beams that scan in a circular pattern. When the microwave pulse encounters precipitation particles in the atmosphere, the energy is scattered in all directions, sending some energy back to the radar. These measurements are used to estimate intensity, altitude, precipitation type and motion. Page 14 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Earth-observing satellites can provide frequent estimates of precipitation at a global scale. To do this, satellites carry instruments designed to observe specific atmospheric characteristics such as cloud temperatures and precipitation particles, or hydrometeors. These data are extremely useful for filling in data gaps that exist between rain gauge and ground-based radar sites and offer insights into when, where, and how much precipitation is falling worldwide. Satellite data also provide a unique vantage point. While ground-based instruments can directly measure or estimate how much precipitation falls to the ground, satellite instruments estimate the amount of electromagnetic radiation or energy that is emitted or reflected either from the top of the clouds or from the rain droplets themselves, providing a top-down view. Example of weather satellite is Diwata 1 and Himawari 8. DIMENSION OF RAIN GAUGE The 8-inch diameter gauge used in the National Weather Service is of a standardized design used throughout the world for official rainfall measurements. This standardization provides uniformity, continuity, and credibility of precipitation data worldwide. There are two basic types of the 8-inch gauge: the traditional large gauge has a capacity of 20 inches depth whereas the smaller gauge has a capacity of 7 inches. The 20-inch depth gauge is the norm throughout the National Weather Service. However, other agencies like the U.S. Forest Service often use the smaller gauge. It has also a 8 inch diameter funnel emptying into a graduated cylinder, 1.17 inches in diameter, which fits the container that is 8 inches in diameter and 20 inches depth. If the rainwater overflows the graduated inner cylinder, the lager outer container will catch it. When measurements are taken, the height of the water in the small graduated cylinder is measured, and the excess overflow in the large container is carefully poured into another graduated cylinder and measured to give the total rainfall. SET-UP FOR RAIN GAUGE 1. The gauge should be placed in an area that is protected from the strong winds but is not bothered by obstacles that could either block precipitation from reaching the gauge or cause precipitation to splash towards it. 2. The gauge should be installed 2-5 feet above the ground mounted on the side of a single post. The top of the rain gauge should extend several inches above the top of the mounting post. The mounting post should have rounded, pointed or slanted top to avoid upward splash towards the rain gauge. 3. The rain gauge should be installed at a reasonable distance away from obstacles such as buildings and trees. For example, if a tree is 40ft. tall, the gauge should be placed at least 80 ft. downwind from it. This will help to avoid potential blockage of the rain gauge. It is not always possible to find a perfect location. 4. Avoid large obstacles that could block precipitation. 5. Avoid mounting the rain gauge where sprinklers or other sources of artificial precipitation can affect the data. 6. Make sure the top of the rain gauge is level. 7. Mount the rain gauge so that the heavy rain could not splash into the gauge from any nearby surfaces. Page 15 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Figure 5: Rain Gauge (Source: Ragnurath, H.M. (2006). Hydrology: Principles, Analysis, Design. 2nd Edition) ESTIMATING THE MISSING DATA AND ADJUSTMENT OF RECORDS For frequency analysis of rainfall data, a sufficiently long record is required. It may be so happened that a particular rain-gauge is not operative for part of the month or so (since it is broken or for some other reason), when it becomes necessary to supplement the missing record by one of the following methods: 1. STATION YEAR METHOD In this method, the records of two or more stations are combined into one long record provided station records are independent and the areas in which the stations are located are climatologically the same. The missing record at a station in a particular year may be found by the ratio of averages or by graphical comparison. Example: In a certain year the total rainfall of station A is 75 cm and for the neighboring station B, there is no record. But if the record at A and B are 70 cm and 80 cm, respectively, the missing year’s rainfall at B (say, PB) can be found by simple proportion as: 2. NORMAL RATIO METHOD In this method, simply ratio and proportion process and get the average. Example: Rain-gauge station D was inoperative for part of a month during which a storm occurred. The storm rainfall recorded in the three surrounding stations A, B and C were 8.5, 6.7 and 9.0 cm, respectively. If the record for the stations are 75, 84, 70 and 90 cm, respectively, Estimate the storm rainfall at station D. 3. DOUBLE MASS ANALYSIS The trend of the rainfall records at a station may slightly change after some years due to a change in the environment (or exposure) of a station either due to coming of a new building, Page 16 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 fence, planting of trees or cutting of forest nearby, which affect the catch of the gauge due to change in the wind pattern or exposure. The consistency of records at the station in question (say, X) is tested by a double mass curve by plotting the cumulative annual (or seasonal) rainfall at station X against the concurrent cumulative values of mean annual (or seasonal) rainfall for a group of surrounding stations, for the number of years of record. From the plot, the year in which a change in regime (or environment) has occurred is indicated by the change in slope of the straight-line plot. The rainfall records of the station x are adjusted by multiplying the recorded values of rainfall by the ratio of slopes of the straight lines before and after change in environment. Example: The annual rainfall at station X and the average annual rainfall at 18 surrounding stations are given below. Check the consistency of the record at station X and determine the year in which a change in regime has occurred. State how you are going to adjust the records for the change in regime. Determine the record for the period 1952-1970 for the changed regime. YEAR ANNUAL RAINFALL STATION ANNUAL STATION AVERAGE X (cm) OF 18 STATION (cm) 1952 30.5 22.8 1953 38.9 35.0 1954 43.7 30.2 1955 32.2 27.4 1956 27.4 25.2 1957 32.0 28.2 1958 49.3 36.1 1959 28.4 18.4 1960 24.6 25.1 1961 21.8 23.6 1962 28.2 33.3 1963 17.3 23.4 1964 22.3 36.0 1965 28.4 31.2 1966 24.1 23.1 1967 26.9 23.4 1968 20.6 23.1 1969 29.5 33.2 1970 28.4 26.4 Page 17 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 It can be seen from the figure that there is a distinct change in slope in the year 1958, which indicates that a change in regime (exposure) has occurred in the year 1958. To make the Page 18 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 records prior to 1958 comparable with those after change in regime has occurred, the earlier records have to be adjusted by multiplying by the ratio of slopes m2/m1. The slope is 0.9/1.25. Cumulative rainfall 1958-1970 = 554.5 – 204.7 = 349.8 cm Cumulative rainfall 1952-1957 adjusted for changed environment = 204.7 × (0.9/1.25) = 147.6 cm Cumulative rainfall 1952-1970 (for the current environment) = 497.4 cm record adjusted for the current regime = 497.4cm/19 years = 26.2 cm. MEAN AREAL PRECIPITATION It is the rainfall at a single station. For small areas less than 50 km2, point rainfall may be taken as the average depth over the area. In large areas, there will be a network of rain-gauge stations. As the rainfall over a large area is not uniform, the average depth of rainfall over the area is determined by one of the following three methods: 1. ARITHMETIC MEAN METHOD It is obtained by simply averaging arithmetically the amounts of rainfall at the individual rain-gauge stations in the area. This method is fast and simple and yields good estimates in flat country if the gauges are uniformly distributed and the rainfall at different stations do not vary very widely from the mean. These limitations can be partially overcome if topographic influences and aerial representativity are considered in the selection of gauge sites. 2. THIESSEN POLYGON METHOD This method attempts to allow for non-uniform distribution of gauges by providing a weighting factor for each gauge. The stations are plotted on a base map and are connected by straight lines. Perpendicular bisectors are drawn to the straight lines, joining adjacent stations to form polygons, known as Thiessen polygons. Each polygon area is assumed to be influenced by the rain gauge station inside it, i.e., if P1, P2, P3,.... are the rainfalls at the individual stations, and A1, A2, A3,.... are the areas of the polygons surrounding these stations, (influence areas) respectively, the average depth of rainfall for the entire basin is given by The results obtained are usually more accurate than those obtained by simple arithmetic averaging. The gauges should be properly located over the catchment to get regular shaped polygons. However, one of the serious limitations of the Thiessen method is its non- flexibility since a new Thiessen diagram has to be constructed every time if there is a change in the rain gauge network. 3. ISOHYETAL METHOD the point rainfalls are plotted on a suitable base map and the lines of equal rainfall (isohyets) are drawn giving consideration to orographic effects and storm morphology. The Page 19 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 average rainfall between the successive isohyets taken as the average of the two isohyet values are weighted with the area between the isohyets, added up and divided by the total area which gives the average depth of rainfall over the entire basin. This method if analyzed properly gives the best results. Example: Determine the mean areal depth of rainfall over the basin by the three methods. STATION RAINFALL RECORDED A 8.8 B 7.6 C 10.8 D 9.2 E 13.8 F 10.4 G 8.5 H 10.5 I 11.2 J 9.5 K 7.8 L 5.2 M 5.6 N 6.8 O 7.4 Page 20 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Solution: Using Arithmetic Mean Method: Page 21 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Using Thiessen Polygon Method: Using Isohyetal Method DEPTH-AREA-DURATION ANALYSIS Rainfall rarely occurs uniformly over a large area; variations in intensity and total depth of fall occur from the center to the peripheries of storms. The average depths of rainfall are plotted against the areas up to the encompassing isohyets. It may be necessary in some cases to study Page 22 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 alternative isohyetal maps to establish maximum 1day, 2-day, 3 day (even up to 5-day) rainfall for various sizes of areas. If there are adequate self-recording stations, the incremental isohyetal maps can be prepared for the selected (or standard) durations of storms, i.e., 6, 12, 18, 24, 30, 42, 48 hours etc. Steps in drawing a DAD Curves: 1. Determine the day of greatest average rainfall, consecutive two days of greatest average rainfall, and like that, up to consecutive five days. 2. Plot a map of maximum 1-day rainfall and construct isohyets; similarly prepare isohyetal maps for each of 2, 3, 4 and 5-day rainfall separately. 3. The isohyetal map, say, for maximum 1-day rainfall, is divided into zones to represent the principal storm (rainfall) centers. 4. Starting with the storm center in each zone, the area enclosed by each isohyet is planimetered. 5. The area between the two isohyets multiplied by the average of the two isohyetal values gives the incremental volume of rainfall. 6. The incremental volume added with the previous accumulated volume gives the total volume of rainfall. 7. The total volume of rainfall divided by the total area up to the encompassing isohyet gives the average depth of rainfall over that area. 8. The computations are made for each zone and the zonal values are then combined for areas enclosed by the common (or extending) isohyets. 9. The highest average depths for various areas are plotted and a smooth curve is drawn. This is DAD curve for maximum 1-day rainfall. 10. Similarly, DAD curves for other standard durations (of maximum 2, 3, 4 day etc. or 6, 12, 18, 24 hours etc.) of rainfall are prepared. GRAPHICAL REPRESENTATION OF RAINFALL The variation of rainfall with respect to time may be shown graphically by 1. Hyetograph 2. Mass Curve HYETOGRAPH A hyetograph is a bar graph showing the intensity of rainfall with respect to time and is useful in determining the maximum intensities of rainfall during a particular storm as is required in land drainage and design of culverts. Page 23 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 MASS CURVE A mass curve of rainfall (or precipitation) is a plot of cumulative depth of rainfall against time. From the mass curve, the total depth of rainfall and intensity of rainfall at any instant of time can be found. The amount of rainfall for any increment of time is the difference between the ordinates at the beginning and end of the time increments, and the intensity of rainfall at any time is the slope of the mass curve (i.e., i = ∆P/∆t) at that time. A mass curve of rainfall is always a rising curve and may have some horizontal sections which indicates periods of no rainfall. The mass curve for the design storm is generally obtained by maximizing the mass curves of the severe storms in the basin. Self-Help: You can also refer to the sources below to help you further understand the lesson: Jain, S. K., Singh V. P. (2019). Engineering Hydrology: An Introduction to Processes, Analysis, and Modeling (1st Ed.) Gribbin, J.E. (2014). Introduction to Hydraulics and Hydrology with Applications for Stormwater Management. 4th Edition. Cengage Learning Page 24 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Ragnurath, H.M. (2006). Hydrology: Principles, Analysis, Design. 2nd Edition. New Age International Publishers Let’s Check Activity 1. Identify the following process of hydrologic cycle that fits in the definition. ____________1. is any type of water that forms in the Earth’s atmosphere and then drops onto the surface of the Earth. ____________2. Flow of water that is not absorbed into the soil. The overflow from the surface to the bodies of water like river. ____________3. Water that comes from the river, seas, etc. transfer into a gas or water vapor. ____________4. The process by which the water vapor changes to a liquid. __________5. is beneath most places on the land surface. This water is contained in the voids within the underlying geologic material, and the water-bearing formations are called aquifers. __________6. Is the process by which plants and animals including human gives off water vapor through pores and evaporate it. __________7. From root zone, water will move down till reach to the aquifer. __________8. Rain falls into the ground infiltrates from the surface up to the root zone. __________9. When rain falls on the earth's surface, some of it strikes vegetation, buildings, and other objects. This rain is said to be intercepted. _________10. The scientific study of the properties, distribution, and effects of water on the earth’s surface, in soil and underlying rocks, and in the atmosphere. Activity 2. In this activity, you are required to elaborate your answer to each of the questions below. 1. What is the difference between Hydrology and Hydraulics? Cite an Examples. ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ 2. How hydrologic cycle affects the daily life of human being? ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Page 25 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ 3. Explain the process on Cloud Formation. ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ 4. What are the environmental problems that affects the watershed? How can we protect it? ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ 5. What are the difference between the ground-based instruments and earth-observing satellites in measuring precipitation? ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Page 26 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 RUBRICS FOR ESSAY FOCUS CONTENT ORGANIZATION STYLE CONVENTIONS (20%) (20%) (20%) (20%) (20%) 4 Sharp, Substantial, Sophisticated Precise, Evident distinct, specific, arrangement of illustrative Control of controlling and/or content with use of grammar, point illustrative evident and/or variety of mechanics, made content subtle words and spelling, usage about a demonstrating transitions sentence and sentence single strong structures formation topic with development to create evident and consistent awareness sophisticated writer’s of task ideas voice and tone appropriate to audience 3 Apparent Sufficiently Functional Generic use Sufficient point developed arrangement of of variety control of made content with content that of words grammar, about a adequate sustains a and mechanics, single elaboration or logical order sentence spelling, usage topic with explanation with some structures and sentence sufficient evidence or that may or formation awareness transitions may not of task create writer’s voice and tone appropriate to audience 2 No Limited Confused or Limited Limited apparent content with inconsistent word control of point but inadequate arrangement of choice and grammar, evidence elaboration or content with or control of mechanics, of a explanation without sentence usage, and specific attempts at structures sentence topic transition that inhibit formation the voice and tone 1 Minimal Superficial Minimal control Minimal Minimal evidence and/or of content variety in control of of a topic minimal arrangement word grammar, content choice and mechanics, minimal spelling, usage control of and sentence sentence formation structures Page 27 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 In a Nutshell Activity 1. Take a picture of the current situation of the clouds in your area. Describe it based on the color, size, thickness, and altitude. And from that, determine the type of cloud. Paste it in an A4 size of paper and send in the blackboard. Activity 2. Find a website or a weather company that discuss or give information about the daily weather in your area. Obtain the 1week weather forecast and its corresponding 24 hour temperature. Then, create a video with a medium of English, Filipino and Cebuano presenting the data that you’ve collected like a weather forecaster. Then pass the video in Blackboard LMS. Activity 3. Delineate the watershed assigned to you. Follow the steps in delineating a watershed. RUBRICS FOR PERFORMACE TASK MAKE FOLLOWING PRESENTATION PUNCTUALITY RELEVANT THE OF ACTIVITIES (25%) OBSERVATION PROCEDURE AND (25%) (25%) SOLUTIONS (25%) 4 Student All procedure The Student consistently use were followed presentation of passed the more than one activities and activities sense to observe solutions were before and on objects and organized and time. events neat 3 Student uses Followed most Most of the Student more than one procedures. activities and passed the sense to observe solutions were activities 10 with little organized and minutes after guidance neat the deadline. 2 Student continue Followed some Some of the Student to use the sense procedures. activities and passed the of sight to solutions were activities 30 observe and can organized and minutes after use other senses neat the deadline. with some prompting 1 Student can use None of the None of the Student the sense of sight directions were activities and passed the to observe and followed solutions were activities 60 events and sort organized and minutes after these accordingly neat the deadline. Big Picture Week 4-5: Unit Learning Outcomes-Unit 2 (ULO-2): At the end of the unit, you are expected to a. Characterize the importance of evapotranspiration and interception in the hydrologic cycle. b. Discover the behavior of water through surface and subsurface runoff phenomenon. Page 28 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 Big Picture in Focus: ULO-2a. Characterize the importance of evapotranspiration and interception in the hydrologic cycle. Metalanguage The most essential terms below are defined for you to have a better understanding of this section in the course. 10. Evaporation. Water that comes from the river, seas, etc. transfer into a gas or water vapor. 7. Transpiration. The giving off of water vapor by the plants and animals. 8. Interception. Precipitation that strikes off to the buildings, vegetation and others before it comes down to the surface. Essential Knowledge We must know the importance of evapotranspiration and interception process in the hydrologic cycle. It is important to deal with it to be able to determine the movement of water cycle and maintain the water balance. WATER LOSSES There are several factors that create water losses. The following factors are: 1. Interception loss-due to surface vegetation Ex:(held by plant leaves) 2. Evaporation from water surface. 3. Evaporation from soil surface, appreciably when the ground water table is very near the soil surface. 4. Transpiration from plant leaves. 5. Evapotranspiration for consumptive use from irrigated or cropped land. 6. Infiltration into the soil at the ground surface. 7. Watershed leakage ground water movement from one basin to another or into the sea. EVAPORATION Evaporation from free water surfaces and soil are of great importance in hydro- meteorological studies. The factors affecting evaporation are air and water temperature, relative humidity, wind velocity, surface area (exposed), barometric pressure and salinity of the water, the last two having a minor effect. The rate of evaporation is a function of the differences in vapour pressure at the water surface and in the atmosphere, and the Dalton’s law of evaporation is given by: E = K (ew-ea) where K= constant, E = daily evaporation ew= saturated vapour pressure at the temperature of water ea= vapour pressure of the air (about 2m above) if we consider the wind velocity, it becomes: E = K(ew-ea)(a+bV) Where K, a, and b are constant, V= Wind velocity Higher the temperature and wind velocity, greater is the evaporation, while greater the humidity and dissolved salts, smaller is the evaporation. Page 29 of 139  College of Engineering Education 2nd Floor, B&E Building Matina Campus, Davao City Telefax: (082) 296-1084 Phone No.: (082)300-5456/300-0647 Local 133 METHOD IN ESTIMATING EVAPORATION 1. WATER BALANCE METHOD This technique relies on measuring the change in storage, all inflows, and all outflows, except evaporation, for a body of water. The measuring done; evaporation may be calculated readily: where I = inflows O = outflows ∆S = change in storage. E=I – O ± ∆S Most bodies of water have several outflow and inflow terms. The seepage term, which may have both inflow and outflow components, is virtually impossible to assess accurately independent of evaporation. Hence, the water budget technique rarely is useful. 2. ENERGY BUDGET METHOD In this approach to estimating evaporation from a free-water surface, a thermal budget for the water body must be developed. The equation for energy used in evaporation is. He = Hs + Hw – Hl – Hc – Hr Where: He = energy used for evaporation Hs