Assignment on: Runoff and flooding (Drainage Pattern, Stream Flow Velocity, River-stage and Discharge.)
- 1. Page | 1 Jatiya Kabi Kazi Nazrul Islam University Assignment on: Runoff and flooding (Drainage Pattern, Stream Flow Velocity, River-stage and Discharge.) Course Name: Hydrology and Hydrogeology. Course Code: ESE-2101 DATE OF SUBMISSION: August 25, 2022 SUBMITTED BY Mozakkir Azad Roll no: 20103429 Session: 2019-2020 2nd Year 1st Semester Department of Environmental Science and Engineering SUBMITTED TO DR. ASHRAF ALI SEDDIQUE Professor Department of Environmental Science and Engineering. Jatiya Kabi Kazi Nazrul Islam University Trishal, Mymensingh
- 2. Page | 2 Content Topics Page No. Introduction 03 Hydrology 04 Runoff of water 04 Flooding 05 Drainage patterns 06 Importance of Drainage Patterns 09 Stream Flow Velocity 10 Importance of stream flow 11 River Stage and Discharge 12 River Stage 12 Discharge 13 Effects of Human activities on River Stage 14 Conclusion 14 References 15
- 3. Page | 3 Introduction Water is one of our most important natural resources. Without it, there would be no life on earth. The supply of water available for our use is limited by nature. Although there is plenty of water on earth, it is not always in the right place, at the right time and of the right quality. Adding to the problem is the increasing evidence that chemical wastes improperly discarded yesterday are showing up in our water supplies today. Hydrology has evolved as a science in response to the need to understand the complex water systems of the Earth and help solve water problems. Hydrologists play a vital role in finding solutions to water problems, and interesting and challenging careers are available to those who choose to study hydrology. Water is one of our most precious natural resources. Without it, there would be no life on earth. Hydrology has evolved as a science in response to the need to understand the complex water system of the earth and help solve water problems. This hydrology primer gives you information about water on Earth and humans' involvement and use of water. The water cycle, also known as the hydrological cycle or the H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice, fresh water, saline water and atmospheric water is variable depending on a wide range of climatic variables. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, runoff, and subsurface flow. In doing so, the water goes through different phases: liquid, solid, and gas.
- 4. Page | 4 Hydrology Hydrogeology is the study of the movement of water through the subsurface geologic environment. This article reviews the basic concepts of groundwater flow through sediments and bedrock, and the key equations that are used to quantify the rates of groundwater flow. These equations are central to the formulation of numerical simulation models now routinely used to predict how a groundwater system will respond to imposed stresses, such as large-scale groundwater withdrawals or climate change. Flood flows in a channel result from the off-site flows of water from hundreds of ecosystems in its drainage basin during rapid snow melting or a summer rainstorm. Although these outflows are different from different contributing systems, and reach the channel in different times, it still is possible to gain a large amount of usable information about the flow regime in a channel if we hypothesize a rainstorm that produces a uniform depth of “excess” (or infiltrated) water over all the contributing ecosystems. It integrates the rise, peak, and decline characteristics of the flows from each of many ecosystems. Runoff is the water that is pulled by gravity across land’s surface, replenishing groundwater and surface water as it percolates into an aquifer or moves into a river, stream or watershed. The type, intensity and distribution of precipitation affects runoff, as does the slope, vegetation and topography of the land over which it travels. Climate change affects the patterns of runoff because as more precipitation falls as rain and less as snow, the snow melts faster as it is hit by rain. Furthermore, warmer temperatures change runoff patterns. Runoff of water There are three major types of runoff depending on the source: surface flow, interflow, and base flow. 1.Surface Flow: Surface water flow is simply the continuous movement of water in runoff or open channels. This flow is often quantified as discharge, defined as the rate of flow or the volume of water. that passes through a channel cross section in a specific period of time. Surface flow is water that has remained on the surface and moves as overland or channel flow
- 5. Page | 5 2. Interflow: Interflow is water that has entered the upper soil profile and then moves laterally through the soil profile and reappears as surface flow at a downstream point. The lateral flow is caused by a relatively impervious zone that prevents further downward movement. Interflow may be a significant part of total direct runoff under certain soil, geological and land use conditions. It is common in forested areas on moderate or steep slopes with permeable soils of moderate depth over bedrock. The forest and ground litter provide high infiltration for water to enter the soil, and the slope provides the energy for lateral flow. 3. Base flow: Base flow is water from a saturated ground water zone that underlies most land areas. It usually appears at a downstream location where the channel elevation is lower than the ground water table. Ground water provides the stream flow during dry periods having minor or no precipitation. Ground water may enter a channel as seepage along the lower banks of the channel. This type of flow is not normally a big contributor to flood runoff. Flooding Floods are the most frequent type of natural disaster and occur when an overflow of water submerges land that is usually dry. Floods are often caused by heavy rainfall, rapid snowmelt or a storm surge from a tropical cyclone or tsunami in coastal areas. Flooding occurs in known floodplains when prolonged rainfall over several days, intense rainfall over a short period of time, or a debris jam causes a river or stream to overflow and flood the surrounding area. Base flow is water from a saturated ground water zone that underlies most land areas. It usually appears at a downstream location where the channel elevation is lower than the ground water table. Ground water provides the stream flow during dry periods having minor or no precipitation. Ground water may enter a channel as seepage along the lower banks of the channel. This type of flow is not normally a big contributor to flood runoff. Causes of flooding Heavy Rains Overflowing Rivers.
- 6. Page | 6 Broken Dams. Urban Drainage Basins. Storm Surges and Tsunamis. Channels with Steep Sides. A Lack of Vegetation. Melting Snow and Ice. Drainage Patterns Drainage Pattern is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. The pattern created by stream erosion over time reveals characteristics of the kind of rocks and geologic structures in a landscape region drained by streams. Drainage patterns are classified on the basis of their form and texture according to slope and structure. Their shape or pattern develops in response to the local topography and subsurface geology. River segments inside a river network can be organized in five types of drainage pattern. Figure 1: Flooding
- 7. Page | 7 Depending on the slope of the land, underlying rock structure as well as the climatic conditions of the area, the streams within a drainage basin form certain patterns. These are dendritic, trellis, rectangular, and radial patterns. Types of Drainage Patterns Drainage patterns or nets are classified on the basis of their form and texture. Their shape or pattern develops in response to the local topography and subsurface geology. Drainage channels develop where surface runoff is enhanced and earth materials provide the least resistance to erosion. 1.Dendritic pattern: This pattern develops where the river channel follows the slope of the terrain. The stream with its tributaries resembles the branches of a tree, thus the name dendritic. Figure 1: Dendritic pattern 2.Trellis pattern: A river joined by its tributaries, at approximately right angles, develops a trellis pattern. A trellis drainage pattern develops where hard and soft rocks exist parallel to each other.
- 8. Page | 8 3.Rectangular pattern: A rectangular drainage pattern develops on a strongly jointed rocky terrain. Figure 2:Trellis pattern Figure 3: Rectangular pattern
- 9. Page | 9 4.Radial pattern: It develops when streams flow in different directions from a central peak or dome-like structure. Importance of Drainage Patterns Drainage pattern recognition helps to provide a qualitative description of the terrain for analysis and classification and is useful for terrain modelling and visualization and applications in environment. Much research has been done on the description of drainage patterns in geography and hydrology. Drainage Pattern is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. The pattern created by stream erosion over time reveals characteristics of the kind of rocks and geologic structures in a landscape region drained by streams. Streams can reduce the pollution that flows to downstream rivers, lakes, bays, and coastal waters. They are able to retain sediments and excess nutrients, such as nitrogen and phosphorus, and prevent these pollutants from traveling further downstream where they could cause algal blooms or dead zones. Figure 4:Radial pattern
- 10. Page | 10 Stream Flow Velocity Streamflow is the flow of water in streams and other channels, and is a major element of the water cycle. It is one component of the movement of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel. The velocity of a river is determined by many factors, including the shape of its channel, the gradient of the slope that the river moves along, the volume of water that the river carries and the amount of friction caused by rough edges within the riverbed. The velocity is determined by multiplying the average depth of the stream by the width of the stream to find the area in ft2. Divide the distance traveled by the average travel time to find the velocity of the stream in ft/sec. Figure 5; Stream Flow Velocity
- 11. Page | 11 Factors That Affect Velocity m = mass (in kilograms) g = gravitational acceleration of the earth. h = height above earth's surface (in meters) v = velocity (in meters/sec) Importance of stream flow Streamflow information is required to determine how much water is available in different locations so the citizens can make informed decisions about growth and to help assure there is an adequate water supply even during periods of drought Flow is a function of water volume and velocity. It is important because of its impact on water quality and on the living organisms and habitats in the stream. Large, swiftly flowing rivers can receive pollution discharges and be little affected, whereas small streams have less capacity to dilute and degrade wastes. Changes in stream flow are associated with shifts in salmon habitat, water temperature increases, nutrient availability, and sediment levels. These changes can impact both human uses and the life cycles of salmon and other aquatic life.
- 12. Page | 12 River Stage and Discharge Water or river level is a measure the depth of water in a river at a specific location. Scientists also refer to the measurement of the level of water in a river relative to an arbitrary point (e.g. the river bed) as ‘river stage’. River water level is also important for the health of a river as many plant and animal species need specific ranges of water level at different times of the year We also use water level to calculate how much water is flowing through a river per unit of time known as ‘discharge’. River Stage The Water Level is defined as the height, in meters above the geoid, of the reflecting surface of continental water bodies. It is observed by space radar altimeters that measure the time it takes for radar pulses to reach the ground targets, directly below the spacecraft (nadir position), and return. Hence, only water bodies located along the satellite's ground tracks can be monitored, with a quality of measurement that not only depends of the size of the water body, but also on the reflecting targets in its surroundings such as topography or vegetatio Figure 7: River Stage Figure 6;River stage
- 13. Page | 13 Discharge In hydrology, discharge is the volumetric flow rate of water that is transported through a given cross- sectional area. It includes any suspended solids (e.g. sediment), dissolved chemicals (e.g. CaCO3(aq)), or biologic material (e.g. diatoms) in addition to the water itself. Terms may vary between disciplines. For example, a fluvial hydrologist studying natural river systems may define discharge as streamflow, whereas an engineer operating a reservoir system may equate it with outflow, contrasted with inflow. As the rain starts to get heavy, the soil may be saturated, thus there is an increase in surface run off. This causes water to start flowing into the river channel, causing the level of discharge to increase, making the line go up positively. There are several factors that affect stream discharge. The velocity of the water affects it; faster water means more passes per second so more discharge. The width and depth of the river also affects it; a larger river at the same speed will have higher discharge. Figure 8:Discharge of water
- 14. Page | 14 Effects of Human activities on River Stage Humans abstract (remove) water from rivers to use in our homes, farms and industries. In areas of the UK with a chalk geology we often extract water from the ground (i.e. groundwater) for domestic water supply. Because chalk rivers depend on groundwater for their flow (> 75% of the water in a chalk river comes from the ground) then using groundwater for domestic supply can reduce the level of water in the river. This means that stretches of the river can dry up at unexpected times in the year, or for longer periods of time than might be desirable or healthy for fish. Humans also affect the speed and extent to which water levels can change in our rivers. When we create hard surfaces such as roads and pavements we alter the flow of rain water which moves over our street surface and into drainage pipes, instead of through the soil to the groundwater below. This flow of water is called ‘urban runoff’. This rapid flow of runoff means that water levels in chalk rivers with an urban catchment will respond more quickly to rainfall than might occur naturally. Also, only a little water is lost to the ground, so a greater volume of water reaches our rivers. Urban runoff may carry with it the pollutants that have been deposited on the road and pavement surfaces (e.g. metals and oils). Conclusion Hydrology is an extremely important field of study, dealing with one of the most valuable resources on Earth: water. All aspects of the Earth's available water are studied by experts from many disciplines, from geologists to engineers, to obtain the information needed to manage this vital resource. It is an important field where the people who study hydrology (which are called hydrologists) use their knowledge and expertise to combat water pollution, protect the earth’s water resources, and provide engineering hydrology – which is an engineering specialty focusing on water resources. Water cycle is another important part of it. The water cycle is an extremely important process because it enables the availability of water for all living organisms and regulates weather patterns on our planet. If water didn't naturally recycle itself, we would run out of clean water, which is essential to life. Hydrology and geology are so compactly inter related to each other.
- 15. Page | 15 References 1. www.alamy.com 2. www.researchgate.net 3. www.climate.copernicus.com 4.www.hydrology.bwdb.gov.bd 5. https://www.aiche.org/