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カーブナンバーラスターの作成

John_Herrera

カーブナンバー（CN）ラスターの作成方法を調査しています。都市部の流出深さを計算しています。Arc Hydro Toolsチームには、地形前処理ワークフローのケーススタディに似たフォローできるワークフローがありますか？ケーススタディのワークフローは非常にわかりやすいです。CN作成に関するいくつかのビデオを確認しましたが、それぞれ少し異なるワークフローがありました。<\/P>

さらに、NLCD土地被覆によるカーブナンバー（CN）の照合表はありますか？インターネット上のさまざまなサンプルを調査していると、わずかに異なる数値が見られます。使用する予定だった表のスクリーンショットを添付しました。ご助言とご指導をよろしくお願いいたします！<\/P>

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Water Resources

Arc Hydro

Accepted answers

DeanDjokic

John,

The Pct* fields indicate percentage (0-100) of specific soil type * in the polygon you are representing. Ideally, the sum of all the Pct* fields per polygon will add up to 100. Tool help has explanation on how the numbers are used. What numbers to actually put in will greatly depend on you location - this goes both for the CN as well as Pct* numbers. It might also depend on the type of modeling you are doing (e.g. if you are modeling hydrologic system response to year 2050 conditions you might use different numbers than if the modeling is for today conditions - in addition to different land use polygon extents). There are some "generic" numbers in the literature and online resources (search "hydrologic soil group") that you can use as a starting point, but you really need to be careful in using them as typically they are not correct for your specific geography. Living Atlas has some good resources if you want to use "global" datasets.

Dean

DeanDjokic

John,

No need - the terrain is used only as a reference for extent, snap raster, and cell size.

Dean

DeanDjokic

John,

Arc Hydro has a tool called "Generate CN Raster" (in the H&H Modeling -> Utility toolset). It takes three inputs - DEM (used for rasterization of the final CN raster product), land use/soil polygon feature class, and CN lookup table that identifies CN value for combination of LU/soil type. Help for the tool has description of the fields that need to be in FC and table for the tool to work. Please review, and see if that works for you.

As far as the CN per NLCD values goes, you have to be very careful. CN values are LOCAL, so the same land use/soil combination can (and should) have different values for different geographic locations - similar, but different. That is why you will see different numbers depending on the literature you are using as a reference. In the US, local NRCS offices maintain such local information (and some other agencies might use their own - e.g. in a hydrology manual for a county). That was one of the drivers in our tool design - we wanted to provide you with the option to specify your own table and through it control the assignment of CN values.

Dean

All comments

John_Herrera

Thank you! I see the Arc Hydro Docs documentation via esrips.github.io. I completely overlooked this resource. Fantastic! Tool Documentation section...🙏 Thanks again for your time! I greatly appreciate it!

John

DeanDjokic

John,

Dean

John_Herrera

The Generate CN Raster tool requires (5) attribute fields that must be populated: LandUse, PctA, PctB, PctC, PctD. Can you please advise what values to populate these fields with? LandUse, I suspect land classification code. I'm not sure about the Pct fields.

John_Herrera

Thank you, Dean! I greatly appreciate your time!

John

DeanDjokic

John,

No need - the terrain is used only as a reference for extent, snap raster, and cell size.

Dean

John_Herrera

Hello, Dean!

Thank you for your advice! Do I have to run terrain pre-processing on the DEM prior to using it in the Generate CN Raster tool?

John

DeanDjokic

John,

Dean

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