I strongly concur with and had the same comments as:
Additional point to the Section A.5.4 about limiting 10% deviation of drainage area. This should be rephrased to be a suggestion/recommendation, because local agencies take the terminology as "should" as equivalent to "shall." If should by DEQ definitions is meant to be recommendation/goal to strive for, please define that somewhere because local agencies will not grant waivers or variances for anything listed in the SWM Hanbook as a requirements, because to them the Handbook/Specs are equivalent to laws.
If "should" really does mean "shall" and is a strict requirement, I understand it is ideal to maintain predevelopment divides, but its not feasible to set a restrictive percent deviation when detention at every single outfall is not feasible due to the downstream receiving conditions. Especially in very rural situation where downstream properties don't have an defined receiving channel to discharge a detention system to because the watershed is rural and does not concentrate, it sheet flows or shallowly runs off onto neighbor properties. Those situations a downstream property can already be affected by flooding and erosion due to the rural nature and having large amounts of sheet flow area that doesnt have a concentrated outfall. So they don't have the ability to install a detention system to maintain predevelopment flows because of a lack of a defined channel to discharge to. The solution in those situation are to send drainage area to another watershed that does have a defined receiving channel, which is inevitably always more than a 10% deviation of the drainage area because impervious area generated more than 10% runoff than predevelopment conditions of forests and lawns. This happens on every one of my byright rural subdivisions where I am just installing a few house on multiple multi acre lot that predevelopment wise sheet flows to an adjacent property that would be problematic to have increased volumes of sheet flow. So I install storm sewer and send the lots drainage area to another outfall where there is a detention facility that can be constructed. That outfall is compliant with regulations so it shouldnt matter if any watersheds change by 10%. It should be phrased as recommendation to strive for as said previously.
Any other comment not listed in this list made by others I agree with as well.