Reddit reviews Open-Channel Hydraulics

Good for you for trying to learn. I'll shotgun some information at you here and maybe that'll give you some good leads to get going. I'll be honest, this is a bit of a pulling a thread on a sweater situation. A great many of the design methods used for design of detention ponds, weirs, inlet/outlet control structures, and pipes in general are pretty simple, but the basic assumptions behind them require much more knowledge to ensure safe and competent design. But regardless, it's not rocket science, and any good engineer will help you out when they see the potential for you to help them out more.

Mannings Equation. This is the basis for all gravity flow calculations. Learn it, love it.

Open Channel Hydraulics by Ven Te Chow is the bible for open channel hydraulics. It's 50 years old, but it's by far the easiest text to actually read and understand. It may be tough to directly connect the science to your work at first, but this is where it all comes from.
http://www.amazon.com/Open-Channel-Hydraulics-Ven-Te-Chow/dp/1932846182/ref=tmm_pap_title_0

Both the FWHA and TXDOT have some good design manuals and research paper type stuff that you can learn a lot of direct design methods.
http://www.fhwa.dot.gov/engineering/hydraulics/highwaydrain/index.cfm
http://onlinemanuals.txdot.gov/txdotmanuals/hyd/index.htm

On the hydrology side, the NWS has done a lot of research on rainfall patterns. They have a ton of information, but here's a link to the seminal TP40 paper that many current IDF curves are derived from.
http://www.nws.noaa.gov/oh/hdsc/PF_documents/TechnicalPaper_No40.pdf

One last thing. I've used Civil 3D every day since it came out, and I still haven't successfully used the Storm & Sanitary add-on. I admit it does look cool, but I could never customize them enough for each City's calculation requirements, and ultimately they weren't worth the trouble for me. You need software for water system modeling and flood modeling, but basic storm and sanitary design is spreadsheet stuff.

Good luck!

Water Resources Engineering - Larry W. Mays or Applied Hydrology - Te Chow for engineering hydrology. They are somewhat outdated in not including some new methods (like ML methods) but both solid for the fundamentals. There is also a PDF copy of the latter floating around if you do a google search.

Chow's Open-Channel Hydraulics book is also great (for channel and hydraulic structures design, non-pressurized), but mind numbing to go through. Also, Fluid Mechanics - Frank White for general fluid mechanics overview.

Finally, although I've not personally read/used it, HEC-22 is a design manual for urban drainage systems and Advanced Water Distribution Modeling and Management for modeling/design of water distribution systems.