What is does an areal flood warning mean exactly?
There are three main types of flood warnings issued: Flash flooding - a flood that occurs within 6 hours of excessive rainfall and that poses a threat to life and/or property. Ice jams and dam failures can also cause flash floods. River flooding - any high water flow, overflow, or inundation event which is threatening lives and property along main stem rivers. Areal flooding - any high water flow, overflow, or inundation in a defined area such as a group of counties or an area along a river or stream which threaten lives and property that is not covered by an river flood, or flash flooding. The main difference between flash floods and areal floods is that areal flooding applies to longer duration precipitation, (greater than six hours), causing slow rises on rivers and streams. http://www.crh.noaa.gov/lot/severe/wxter... http://www.erh.noaa.gov/rnk/Newsletter/S... http://www.erh.noaa.gov/rnk/Research/fla... updated
Why does a river change its course?
Change in River course occurred due to multiple factor like amount of flow of water , fluctuation in the intensity of water flow ,rate of erosion , sedimentation.Firstly, the fast flowing rivers are generally prone to silting up as they surge down the hills and spread out on the plains; thereby allowing sand and suspended matter to deposit in their slower, wider depths. Over time, the deposits create resistance, forcing the river to move to an area of lower resistance. This is why rivers change their courses.Secondly, the nature’s fury such as earthquakes, landslides and hurricanes can also change a river’s course.Thirdly, human activity and climate change are also responsible for change in river course. For example, climate change has triggered the melting of glaciers more quickly thus, the volume of water in rivers has been on the rise, resulting in greater force of flow.( In simple words, river changes its course when it overflow during flooding by cutting bunds. The overflow of river makes new channels and change its course. )
What does flow actually mean in electricity?
Firstly, I would advise you not to use the word electricity other than to refer to a topic of study or as a type of utility bill. I am pretty sure you mean “electric current”.I live in an area where the tides are large and rise /fall by up to 12 metres twice each day. There is also a small river which flows out to sea.Let’s say that a million metres^3 of water that fell as rain flows out to sea each day. As the tide rises, for about 4 hours before high water, the river flows the wrong way. This is because sea water is travelling back up the river. When the tide falls some hours later, the river flows very much faster as the sea and rain water head out to sea. This keeps repeating. In my mind I can easily separate out the water that simply flows in and then back out because of the tide, from the rain water that starts on the land and ends up out at sea.The sea water has a net flow of zero - what flows up, later flows back out. There is a net flow of rain water - we agreed that it was 1 million m^3 water per day. This net flow is not affected by the tides, although it does appear to confuse things a bit.In a metal, electrons are moving due to thermal energy. It is this movement of electrons that makes metals good thermal conductors. However, if you heat a metal, electrons do not gather at one end. So we can say that there is no net flow of electrons. As many move one way as move the other. ( This has some similarities to the tidal flow in having zero net effect).At the same time, when an electric current flows in a metal wire, the electrons slowly make their way from the negative end to the positive end. This is rather like the rainwater going down the river and ending up out at sea.The actual net movement of electrons in a wire is almost always slow. It depends on various factors but if I said it would be less than 1 cm per hour this might give you some feeling for what is going on. We call this the drift velocity.Many people think the electrons will be moving incredibly quickly - because when you operate a light switch, the light comes on almost instantly. The electrons have not travelled from the switch. They were already in the light bulb. They all start moving almost instantly (without delay) but only move slowly.I hope this is the type of thing you wanted to know.
Why does river straightening reduce flood risk?
it allows unhindered flow (faster removal of water) from the area. It doesn't actually reduce flood risk per se, but does reduce it in the area where straightening has occurred. The flood risk downstream is consequently raised because water will arrive downstream faster than before. It diverts the risk in space, but doesn't actually eliminate it. The consequences can be more severe than the problem that was being addressed by the change.
How different is the flow rate at the top of a river to the bottom?
Q: How different is the flow rate at the top of a river to the bottom?Assuming that you mean from the surface to the bottom, in a river where we are looking at laminar flow and a cross section in the direction of flow that is far from either bank and over a bottom with uniform depth and friction, then the difference is total. The water at the surface is the fastest, and as you get closer to bottom the resistance of friction (i.e. flow over rocks, gravel, mud, whatever) will slow the flow. Right at the bottom flow is effectively zero (think of small pockets of water that basically hangs up in depressions and has slow enough turnover to be considered stationary relative to the water at the surface).Impacts with bottom influence water quite far from the bottom as molecules moving in directions other than the direction of flow interact with other molecules. If the flow of the river is not laminar (i.e. a swift current and the interaction of water with friction at the boundaries as a function of flow diameter and viscosity cause turbulent flow) the velocity profile won’t be as uniform, but you will still find your slowest speeds relative to the direction of flow at the bottom.Hope that helps.
How can human activities effect water falls?
There are many, many waterfalls in the world. After all, the vast majority of our planet is covered in water. When land interrupts the flow of water across the landscape, it is here that waterfalls can form.A waterfall is usually a geological formation resulting from water, often in the form of a stream, flowing over an erosion-resistant rock formation that forms a nickpoint, or sudden break in elevation.Interestingly enough there is no standard definition of a waterfall in the modern lexicon. By this we mean there is nothing to define what makes up a waterfall, how to measure a waterfall, and even whether or not a waterfall needs to exist the entire year round.Generally, a waterfall is agreed to consist of a river or stream flowing over a cliff face or slope for a long enough distance that it creates a certain amount of agitation in the water below.Many waterfalls occur where rivers flow over hard rocks whcih overlie softer ones. The hard rocks resist eronsion, while the softer rocks are worn away. The hard lip of the waterfall often overhangs the softer rocks and slabs of hard rock sometimes break off and crash downwards. In this way, waterfalls, like southern Africa's Victoria Falls (whose African name means ' the smoke that thunders'), gradually move upstream. Other waterfalls occur along cliffs, like those bodering steep-sided valleys, or ice-worn troughs.Some waterfalls form in mountain environments in which the erosive water force is high and stream courses may be subject to a sudden catastrophic change.Waterfalls are grouped into ten broad classes based on the average volume of water present on the fall using a logarithmic scale. Humans can effect waterfalls by building dams and increasing the steepness of the slopes.Water pollution can make rock erosion chemically easier at the downfall and at the base. We can also affect the strength of currents on water fall by increasing global warming withpollution. Waterfalls are an important part in the rock cycle and the natural biosphere. It plays an important part in erosion and carrying and moving sediments. They can also wash down wastes. Waterfalls can be very dangerous for rafting and canoeing because it can catch you unexpected and may kill you.
What is the driving force for the heat transfer, electric current and fluid flow?
Heat transfer - the molecules (or atoms at a smaller level) of a substance which are on average moving faster are hotter (more heat). When these molecules come in contact with another substance with slower molecules they impact each other (either physically or through forces) and transfer some of their speed (kinetic energy) to the slower molecules. Thus the temperature decreases in the first substance and increases in the second substance. Electric current - An Electro Motive Force (EMF) created by some means (chemically, magnetically, etc.) exerts a force on charged particles (electrons, protons, ions, etc.). This force causes movement of the charged particles when there is a complete loop back to the other side of the EMF device (such as a battery). Millions of these charged particles passing a point in the conductor per a unit time is measured as an ampere (amp). However, charged particle flow is really proportional to the overall flow of energy that is for all intent purposes instantaneous through the conductor (wire). For example, electrons flow (drift) relatively slow through a wire (in the range of meters per second, can't recall exact number)...however the energy flow is speed of light (or faster depending upon whom you believe. In conclusion all you can really say at this time is that current flow is a predefined number of charge carriers passing a point per unit time (direction can be either way or even both ways depending on the circuit). Fluid flow - Fluid conforms to the shape of its container. So if we have a pipe it will "fill" all areas of the pipe. Fluid is made up a smaller parts (molecules of water for example). In a confined container if these molecules are moving faster (say you heat up the container) they are colliding with their container with more energy (average velocity) and frequency. This is measured as pressure. If you connect a water hose to this container the water will flow as long as the pressure of the water is higher then your outside air pressure. In effect the fluid will flow from the higher pressure to the lower pressure. A city water system increases the pressure by elevating the water container into the air and letting gravity pull the water down (the top of the tank is vented to atmospheric pressure to equalize). This would be an example of potential energy in a gravity field (and not pressure from heat (kinetic) as in the first example).