Good! So it means total length of stream (e.g. 100 meters) divided by total area of a basin, watershed or just an area (e.g. 1000 sqM). Which makes the DD = 0.1M per sqM. The whole idea of DD is to help us understand how well water is drained in a particular area, as long as the formula is applied, different methods of presenting the data can be used
hii, Thanks a lot. It really helped me. I want to ask that after reclassifying the DD, we get DD_wetdry. In that map, the patches of dry areas are far more than the wet areas. So, if you could tell me, what is the basis of the formation of the dry and wet areas ?
hi sir, thanks for the DD calculation video i have some question. 1) stream network which u arrived is digitized manually or from DEM? 2) Is there is possibility to get DD map from a shape file of stream network created with the help of digitization of toposheet.
Thank you Pipas for your comment. 1) Yes the stream network layer was derived from a DEM 2) Yes you can use a stream layer derived from digitalizing a toposheet, but keep in mind the scale of your toposheet so as to understand your results properly.
Hello Sir I have watched your DD tutorial The focal stat gives sum of lengths which is meters. So how can it be drainage density and also based on what the type and settings of the neighborhood is defined?
Hi good tutorial. I have a question. what if the drainage channels are separate lines connecting to each other but separately drawn. I have also another shape file of lines joined together. which one should I use? combined lines or separate ones?
Sir, i want to make drainage density map using fishnet tool and isoline. Now how i can calculate length of rivers of every polygon of a fishnet? How can i make isolines?
hi sir i wanna do dissertation on "improving settlement and urban mobility for congested city" what data should i have or need to collect and what are the tools to be required?
Hello Hamis, there are several waya to approach this and I would suggest you inveat your time in reading some journals on the internet. However, I assume you will be needing these basic datasets(landuse, road geometry, gps point location of congestion areas, digital elevation model). Since you are hoping to improve mobility then after identifying extent of congestion you might want to use the 'cost distance' tool and others to suggest new roads in where needed. I hope this gives a headway.
hi one more question again? drainage density is m/sq.m ie 1/m or per meter right say 0.06 per meter. The focal stat gives sum of lengths which is meters. So how can it be drainage density. One the same line if we have show effect of accumulation large number of channel into a stream of higher order or area as compared to say dry area with less streams, how we can combine this data. DO u know some tool or terminology like flow accumulation map. Plz do reply
Sk Patil OK Sk Patil...your questions are not very clear to me but I hope my answers addresses them. 1. The whole idea of drainage density is to understand the accumulation of stream/river network within your study area either per sq/m or sq/km depending on what unit of measurement you use. 2. So basically the higher the density figures you get from focal statistics, the more drainages there are in that area. 3. With regards to the channels being separate or joined, the idea is to have segmented areas which you are calculating the density for (so you need a boundary shapefile of areas in your study area). 4. It is also very very important to know at what scale/resolution your drainage channel layer is collected in otherwise you will not know what you are really doing. 5. Depending on what scale the data is in, there will be different channels showing up at different scales as some are smaller while others are larger rivers. 6.And off course the flow accumulation tool is what i have used to derive the stream layer in this video. Hope I have at least answered your questions? Best wishes.
Usman Buhari Hi thanks for the reply A) i have diliniated channels from Cartosat 1 DEM for which the spatial resolution is 2.5m in the horizontal plane with accuracy of 8m in horizonatl direction. resampled at 30 m res. So the channels I have got must be at 30 m pixel resolution , Isn,t it? So how can u enlighten me with respect to point 4. B)Also I have dilienated manually , the channes from toposheet having scale of 1:25000, So what resoultion will be another set of drainage channels. Now which set can I use A or B?
Sk Patil If you have the Cartosat DEM, then i would recommend that you use it as you can make several drainage maps by thresholding your flow accumulation using different values to suit your needs. Point 4: I am just saying you need to know the thresholds used to get the drainage channels because only then will you know the amout of drainages you are getting the density for....(e.g the drainages you see in 1:25000 map is more than what you will see in a 1:50000 map). So I recommend you use set A.
Sir can you tell me how do i take out the drainage densities for different rocktypes in a certain area containing granite limestone shale etc, i have shapefile of drainage but i dont have the stream length so how do i calculate that one also.
Hello Vijay, the drainage density analysis is carried out mainly based on the streams/drainages which is this case derived from a digital elevation model. If you have a shapefile showing the boundaries of these rocktypes you can determine the drainage density for each rocktype by using the "Zonal Statistics" tool to calculate the sum of drainage density within the roctypes zones (limestone, granite....) Hope this helps.
sir do i have to clip that part from the polygons which i need to feed in input value raster and what about feature zone data in the initial of dialogue box of zonal statistics.
Hi Vijay, the input value raster should be your drainage density may while the feature zone data should be the rocktypes shapefile showing their boundaries.
Hi Upender, the stream network shapefile is just a polyline feature representing all the small and major river channels in the study area. I converted it to a shapefile so that I can easily do some calculations like (stream length and drainage density) which is in the attribute table.
