ArcGIS T17: How To Calculate Curve Number From Soil Map

[@sweetmemories4448]

Excellent presentation!!!

[@hadikarimi2818]

Nicely Done, Thank you 👍

[@MdArifurRahmahn]

Thanks for watching!

[@斑马条纹男孩]

为什么我在之前的视频下载的数据没有这么多东西呢？

[@knowlege2024]

Thank you such a good tutorial, let know if we have many soil and have many land use then how curve number be given in the single line (attribute table) of the soil?

[@MdArifurRahmahn]

Thank you Salah for the query. If your file is a raster then you have to convert it to feature (i.e., shapefile), then you can see the attribute table.

[@knowlege2024]

@@MdArifurRahmahn can you share your email so that I could I share my query?

[@ravibabuv7152]

Thank you very much superb

[@MdArifurRahmahn]

Most welcome 😊

[@mohammedmakawe1427]

what videos do I need to watch to get to the starting point of this video?

[@MdArifurRahmahn]

Hi, thank you for the query. You can start with the T-01 from my playlist of ArcGIS, or you can attend my training on this software where I demonstrate in details from scratch. For more info send message to [phone] on WhatsApp.

[@mahdaouikamilia3868]

Hello, Please, how we can calculate Initial abstraction Ia? Impervious ? and storage coefficient?

[@MdArifurRahmahn]

You can follow any hydrology book to calculate these model parameters.

[@ciaradoyle2949]

What if we wanted to use more than one land cover value? You just used fair condition grass.

[@MdArifurRahmahn]

Yes, you do that as well if you have the data.

[@fuadmohamed7659]

thank you for your tutorials. its very interested videos. could you plz make video about covid-19 map using ArcGIS?

[@MdArifurRahmahn]

If you download the data it's pretty easy to map the data irrespective of the size and location of the data.

[@JamesBaleLA]

At 9:27 you take the average of B and D for B/D soils. This is incorrect. You want to choose the CN value based on whether the condition of the soils in your analysis are going to be drained or undrained. B/D soils drain well when unsaturated and drain poorly when saturated with water. You should be choosing either B or D based on the assumptions of your analysis or, if you have it available, geotechnical information on the depth of the water table. For instance, a flood study might assume undrained condition while an analysis with shorter recurrence interval and duration might reasonably assume drained conditions. You have to make a judgement call here, you wouldn't want to just average the two values. From the National engineering handbook: "Dual hydrologic soil groups-Certain wet soils are placed in group D based solely on the presence of a water table within 60 centimeters [24 inches] of the surface even though the saturated hydraulic conductivity may be favorable for water transmission. If these soils can be adequately drained, then they are assigned to dual hydrologic soil groups (A/D, B/D, and C/D) based on their saturated hydraulic conductivity and the water table depth when drained. The first letter applies to the drained condition and the second to the undrained condition. For the purpose of hydrologic soil group, adequately drained means that the seasonal high water table is kept at least 60 centimeters [24 inches] below the surface in a soil where it would be higher in a natural state."

[@MdArifurRahmahn]

Thank you James for the comments. I know what you have mentioned here. If you want to run any lumped model using HEC-HMS and if you select CN as loss method, how can you assign one single value of CN for the entire watershed or subbasin? This is why, to make it simple, i have made the engineering judgement. Moreover, if your CN is 81 for B and 86 for D, if you take average or select B or D, what makes the difference? Nothing. And if you even calibrate the model you may need to adjust the % imperiousness which should me constant, but people change it to fix their model. It's beeter to select the dominant soil for any subbasin or even for gridded model, if your model grid is different than your soil grid which is the case always, then you won't be able to restrain your soil grid. You have to adjust it.

[@MdArifurRahmahn]

Here is another one: kzbin.info/www/bejne/pYa9n56Irthmpsk

[@MdArifurRahmahn]

For global land use: kzbin.info/www/bejne/bJy4ln1sYpp-qJY

[@JamesBaleLA]

@@MdArifurRahmahn I understand what you are saying. For the sake of your example, I agree that the model wont likely be very sensitive to say CN of 81 for B and 86 for D as the range between these two values is relatively small, but the same wouldn't be true for the case of A/D if, for example, A is 49 and D is 84. The use of an average, while convenient for this example exercise, is arbitrary and may significantly affect the outcome if the same approach were applied to a more sensitive scenario. I understand that a single value needs to be assigned for the dual groups in the table. In most instances the most conservative approach would be to assume 'D' HSG characteristics for dual soil groups unless you have some reasonable justification to make the assumption that the soil condition is drained for your analysis (depth to water table, ect.). All the same, I appreciate your videos. I'm currently working on some H&H analysis and these GIS tutorials are proving to be a big help, so thank you for your help!

[@MdArifurRahmahn]

@@JamesBaleLA Year, thanks, I have not come across any watershed where I got A/D , it's always B/D. if there is any combination like A/D, then the users need to be careful while selecting the CN. I appreciate your insightful comments. It will help me to be careful in future videos. This is what I expect from people who watch the videos. Becasue I am learning and there is not limit of it. Thank you James again for watching the videos.

[@mingjianwu4277]

sir，how can i download the data of soil？

[@MdArifurRahmahn]

Thank you for the query, If you see other videos, it's there. I have demonstrated how to download the soil and other data set in the previous videos. You can check.

[@JamesBaleLA]

@@MdArifurRahmahn Can you provide a link or the title of the video showing how to download and prepare the soil and land use data prior to the start of this video? Im having trouble finding, but this seems like the exact tutorial i'm looking for. THanks!

[@MdArifurRahmahn]

@@JamesBaleLA Thank you James for the query, here is link: kzbin.info/www/bejne/fGncq6ewgLZ5rrc