Without being able to go through a detail QC, this guidance document has too many technical errors and should not be published. Paid professional engineers who actually practice design in the last 10 years should review these in much more details. For the very very quick review I did, and this does not capture everything because unlike the people who have wrote this guidance document, I don't get paid to correct engineering documents provided by a government agency, here are the several errors I found. Again, someone with practicing design experience needs to re-review this document, otherwise this is going to muddy already murky waters in local agencies review.

1) Increased volumes of sheet flow section 3.305.1 and 3.305.2 incorrectly references that velocity should be checked for the 10-year storm. State code 9VAC25-870-66, ESC handbook, as well as engineering standard, and even earlier references in the guidance document specifically state that erosion is checked based on 2-yr event, NOT 10 year event. So 3.305.1.1 needs to be corrected as permissible velocities are NOT checked against the 10-year event, permissible velocities are to check for erosion which is the 2-yr event.

2-4) Three things are wrong here. A) This table of permissible velocities for sheet flow in 3.305.1.1 is said to be pulling it from Table 5-14 of the VESCH, however table 5-14 of the VESCH specifically states that these permissible velocities are for GRASS LINED CHANNELS, therefore it is incorrectly being used for sheet flow. B) The last 7 rows of the 3.305.1.1 table is NOT from Table 5-14 and is incorrectly referenced, where is the source of these last 7 rows? This goes for ALL the tables that are duplicate of this throughout the guidance document, such as also mentioned in 3.305.2, 3.302.1.C.3. C) In addition, permissible velocities in this table is limited, it’s missing more information found in the VESCH itself such as Table 5-22 for permissible velocities of unlined earthen channels of various soil types. So this is not a holistic outline of all the VESCH information and should be re-checked as I am not an expert myself. Let alone there is so many resources out there, such as VDOT Drainage Manual Appendix 7D-6, 7D-2, VDOT Drainage Manual Table 7-1, that should be acceptable as it has been practiced all over Virginia. Therefore this table should either be expansive enough to include ALL references, or caveat that more acceptable references are allowed not listed in the document.

5) The starred note below the table on 3.305.1.1 also incorrectly states high erodibility soils have k factors greater then 0.35, when in fact per VESCH it is greater then 0.36 in Appendix 6a page VI-44. 

6-7) Section 3.305.2.C to limit sheet flow stating that it is required to equate to 0.1 feet or less for the 10-year storm is grossly incorrect. A) In determining sheet flow, instructions in TR-55 Chapter 3, page 3-3 specifically states it’s for ABOUT 0.1 feet or so, NOT capped at 0.1 or less. B) In addition, TR-55 specifically bases sheet flow off the 2-year 24-hr rainfall event, NOT the 10-year event, as seen in equation 3-3 of TR 55. Velocities is continued to be calculated using the 2-yr event as further seen in Figure 3-2 example 3-1 of the TR-55 handbook. So two things are wrong here.

7) Section 3.302.1.3.A states RCP should be capped at 10 fps for velocities when the industry has accepted 18 fps to avoid abrasion. This information should be removed all together as there is no source for the 10 fps cap and should rely on manufacturer specifications or already established/accepted industry standard.

8) This guidance document is regurgitating wording and phrases pulling from other sources such as the ESC handbook, SWM handbook, state codes, National Engineer Handbook, etc etc. Instead of copy-ing and pasting the regurgitated wording and pulling tables and paragraphs from these references as people should have already read these documents, THIS guidance document should just POINT to where to find it in those documents by being a literal tour guide, hence the word guide. Instead of creating another document with repetitive wording that takes the opportunity to tweek language from its original suggestive wording to making it sound like a requirement in this text. That's not a guidance, that's simply creating new requirements. Case in point = changing sheet from flow ABOUT 0.1 feet or so in TR55, to requiring it to be CAPPED at no more then 0.1 for the incorrect year storm. I cannot go through this entire document arguing over the semantics of the language that is used. But this "guidance document" on the existing regulations that were established nearly 10 years ago is going to create more contention amongst the reviewing and design community ten years too late. Use our tax dollars appropriately and fix it. Thank you.

Thank you for your time, and apologies for any grammatical errors.