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25 feet!? I wouldn't call that a ditch....that's more like a canal. I'm perplex in how you can estimate the depth of a stream bed that is submerged under water. If I was in your situation I think it MAY be possible to perform a very rough estimation as it involves some assumptions. So if you know the Ordinary High Water Mark (OHWM) elevation when the "ditch" was first constructed and at it's current date you can assume the elevation change is due to silt build up. Factor in the slops of the ditch (assuming that didn't erode away) you can do some simple math to get an estimated fill quantity. Now here lies the problem. OHWMs are not typically viewable form an aerial image. In fact sometimes they are hard to find when you are in the field! Unfortunately you can't just assume where the water meets the bank is the OHWM or represents the same flow from one aerial image to another. Streams/ditches/canals typically fluctuate a good bit so you don't want to end up thinking it's sediment causing the water rise when really you were comparing a low flow day to a high flow day. I hope that makes sense. I still don't know how you can get your sediment quantity without some form of field survey.
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07-28-2017
04:38 AM
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Huh, so that's the technical term for what issues I keep fighting so hard to figure out . This will make my Google searching A LOT more useful when trying to find the solution .
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03-02-2017
12:43 PM
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Can you give an example of a floodplain map you are working with? Have you thoroughly searched for an existing GIS floodplain maps? Maybe one that have some information but not all the information you want to have. Can you tell me what area of the world/country you are trying to map the floodplains? Need a little more detail to better get a picture of what your working with and hopefully getting to pointed to a solution.
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02-17-2017
04:58 AM
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Looking at only 'hot spots' won't be very useful if your area you are looking in is fairly large as the hot spots will be mostly at intersections. If the traffic accidents are tracked with other details such as type of crash you could just look at 'lane departure' types of crashes. Or possibly remove all crash data that is within so many feet of an intersection, say 300 or 500 feet. But all of these potential solutions require access to good crash data. Which really is going to help you identify what is truly a dangerous curve. A tight curve with no crash histories I would argue is not a 'dangerous' curve. Then again 1 crash every three years isn't bad at all, and definitely not a 'hot spot'. But if every one of them is a fatal crash since the vehicle falls over a giant cliff I think everyone would agree to be a very dangerous curve. So sorting by severity of injury would help as well....assuming your crash data tracks that as well.
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01-27-2017
05:04 AM
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Are the LOS letter graded or actual numbered? I had a second idea that may prove useful. You could use dots with colors and numbers inside them too to indicate how many lanes at the intersection are at a specific LOS or lower. This would help show the extend of the issue at an intersection. The number of bad lanes to good lanes may also be useful but too difficult to fit clearly in a map. Numbered LOS would be best if you had it so you could separate the barely failing lanes from the greatly failing lanes. Essentially help prioritize the failing lanes/intersection. Indication of travel (east bound) would be very useful information to give, I'll keep that idea in the back of my head for future projects. It's unfortunate they want only static mapping. You'll have to generalize data and hide a good bit of some useful information to show the most pressing information clearly. Depending on the density of some areas multiple maps may be required. That or one very big map, lol. Glad I help you out a bit. If anything I hope I was a catalyst to helping you get to a final solution if none my ideas prove viable.
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07-22-2016
06:02 AM
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"The request was to portray historic traffic data on a map, particularly at intersection in order to view which intersection were leading to long wait times." How is the data given to you? Are they giving you the queue line lengths? Or just LOS (Level of Service) for each lane and then asking you to graphically represent it? I would assume they are giving you LOS per lane. In which case you could rate intersection via color dots for what is the worst LOS lane in that intersection. This way you could map many intersection on one map and see patterns and trends. If one lane has horrible LOS then the intersection as a whole needs individual attention which is why you could get away with just a dot and not identifying the lane in the map. If you want to get more detailed you can have a layer for every type of lane (Left Lane, Left/Thru Lane, Thru Lane 1, Thru Lane 2, etc.) and use the same dot or better a colored sign indicating LOS and travel directions. But with that method you can only show only a couple or just one intersection at a time. If you filter the LOS to show only failing lanes then you could probably get away with more intersections shown on a map. If you want to get real fancy with it you could combine both methods and have the Lane LOS information turn on once you zoom into an intersection. This method would be most useful for a Traffic Engineer to quickly access intersection issues from their desktop or in a presentation setting. If you have no LOS data and they are asking you figure out what intersection are leading to long wait times, well that's a data collecting issue. Turn counts are needed and those kinds of things aren't cheap. An indirect way of figuring out if an intersection is having LOS issues is to look at crash data. Long lines at intersections will have a lot of rear end crashes away from the intersection where drivers weren't expecting to stop so far way from an intersection. For turning LOS you'll see angle crashes. This is especially true for turning lanes that are thru lanes too. Turning traffic causes traffic to build and then thru traffic at the rear of the line will change lanes and get into a crash. These conclusions can really only be vetted by looking at the crash reports filled out by the police. A good police officer will note where the crash is relative to the intersection and sometimes write the drivers reason for their driving actions, "Driver was changing lanes due to backed up traffic." This method is really time intensive task that is usually only done when an intersection has been flag as a high crash area and then a traffic study is done on that road/intersection where every crash report is read and depicted on a map along with the rest of crashes to see patterns and trends. If you let me know what data you are given I may help you figured out a good method to convey the most pertain information and hide the rest of the information in the background.
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07-22-2016
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