Just completed upgrade to ArcGIS 10. Current ArcHydro 9.3.1 will not install. Installer looks for 9.3 products. Looked for updates at ftp site, resource center and the ArcHydro Blog - no luck. Hopefully, Dr. Maidment and his group are on the fix and will have it live soon.
From what I understand, there are no plans to forward engineer Arc Hydro, TAUDEM, HEC-GeoRAS, or HEC-GeoHMS to compatibility with 10. So those of us in the H&H service lines will be sticking with 9.3 for quite some time. This is similar to when ESRI moved from 3.2 to 8.0: note how there are still people using 3.2 because of the investment people made in developing tools to work on the AV 3.x platform. That many more people have made a much more substantial investment in developing tools that work on the 9.x platform, and I suspect that very few people will be migrating to 10 that depend on 9.3 to generate income for them. Severl pals of mine had their IT dept push 10 out like the week it came out, and have had all sorts of problems going back to 9.3 so they could finish projects.
ArcHydro is pretty much fully functional for ArcGIS 10, ver 22.214.171.124 was built Dec 22, 2010 and posted to the Water Resources ftp site, and it bundles AppFramework ver 126.96.36.199.
The embedded Help and Tutorial were updated Nov 15, 2010.
But, as has been well publicized the HEC GeoRAS and GeoHMS will not be updated in the near term for ArcGIS 10. So if your needs center on preprocessing support for HEC RAS or HMS, you'll need to stay with ArcGIS 9.3
Is there a business reason for not upgrading GEO RAS&HMS to work with 10? That affectively guarantees that the entire H&H engineering community won't be spending $$$ (as ESRI would hope) on 10. I am already running into situations where organizations are running into issues after IT blindly updates to 10, only to encounter a user revolt when none of the H&H tools will work. At the university level, we're facing demands from the population that we teach using 10, but what we teach is centered around the application of tools and extensions that are applicable to resource management and engineering, and none of these things work in 10. I'm rather confused about the business case to release a major version change, push its sale with this so-called "certification", yet not support any of the functionality that has made previous versions successful.
Simply put it is not ESRI's decision. The U.S. Army Corps of Engineering, Hydrologic Engineering Center (HEC) is not a commercial entity and their development work on all HEC related H&H software is not bound by business considerations--rather operational and configuration management tied to the needs to the Corps of Engineers.
ArcHydro and the Water Resources Application Framework development, including HEC-GeoRAS/GeoHMS is a collaborative effort on the part of U.S. Governmental, Educational and ESRI Professional services. It continues apace with the needs and requirements of each participant. ESRI has proceeded with development of an ArcGIS 10 ArcHydro extension because it does make business sense. The HEC on the other hand does not yet require an ArcGIS 10 capability at this stage of the HEC-RAS and HEC-HMS projects. The ArcGIS 9.2/9.3 compliant GeoRAS 4.3/GeoHMS 4.2 and GeoHMS 5.0 developmental versions of the software are being maintained by this effort.
ESRI is not the purveyor of HEC-GeoRAS/HEC-GeoHMS, simply a collaborative partner in its development. ESRI hosts, as a public service, access the "developmental" versions of the software. The HEC retains distribution and management of the "official" versions and provides configuration management and technical support for their internal USACE offices.
I'd note that in reality, in an academic, corporate or governmental setting it is a simple matter to maintain ArcGIS 9.x and desired HEC GeoRAS or GeoHMS functionality by retaining seats of ArcGIS 9. ESRI's licensing structure facilitates this and their track record suggests they will continue to support prior versions indefinitely.
There are other commercial purveyors of preprocessors for the HEC RAS/HMS modeling systems, Aquaveo for example, that have implemented ArcGIS 10 capable versions of their software. A route the HEC has no operational need to pursue--yet.