Queimar cursos d'água introduz erro

Question

<\/HEAD>Estou tentando modelar uma bacia hidrográfica com uma resolução mais fina do que a mostrada pelo NHD do meu estado. Eu entendo os processos do Hydro, mas estava me perguntando por que é aceitável queimar os cursos d'água no DEM quando isso não apenas altera a seção do curso d'água do dem em 10M, mas também suaviza as células ao redor. Parece que ao fazer isso se introduziria erro desde o início. <\/SPAN> Após modelar com e sem queimar o NHD no DEM, há claramente diferenças nas camadas de cursos d'água resultantes. Os pontos de observação coincidem mais com os resultados queimados. Isso é apenas a troca? Que o erro total é reduzido ao introduzir um erro leve no início?<\/SPAN> Obrigado<\/SPAN><\/BODY><\/HTML>

LornaMurison · Answer

If you burn the streams only in selected areas like at road crossings (like you are suggesting) or in particularly flat areas, where filling sinks eliminates the stream itself (like I may have to do) don't you then introduce sinks into the stream itself? Can that then be corrected by using fill sinks?

Thanks,

MarkBoucher · Answer

The goal of the DEM reconditioning using Spatial Analyst or Arc Hydro tools is to get the flow direction right. When I work on the stream burning step, I try to minimize the width of the burn by making the stream buffer only 2 cells wide. You may be able to make it just one cell wide, but I vaguely recall that not working well so I've stayed with 2. I work with a 10x10 dem. The walls have to be at least 2 cells wide or you will get "leakage" via the diagonal.

I also minimize where I put the streams to burn. If the rawdem is good for the flow direction, I don't put a line in it. I only put in lines at bridges and culverts. If I have a stream layer, I will buffer the road layer and use that to clip the stream layer so I only have short segments at the stream crossings. Of course I have to review the crossings to make sure the stream polyline is "correct".

So, does burning streams introduce error. Yes. Does the rawdem have errors already? Yes. If you are diligent enough you can make the rawdem better for flow direction determination and minimize the introduced error.