Editing Chesapeake and Ohio Canal (section)

===Waste weirs, spillways, and informal overflows (mule drinks)===
{{multiple image
   | width     = 150
   | image1    = Waste_Weir_Closed_on_C_and_O_Canal.jpg
   | alt1      = Waste Weir
   | caption1  = A waste weir, looking from above.
   | image2    = Spillway_on_C_and_O_Canal.jpg
   | alt2      = A spillway
   | caption2  = A spillway
  }}
To regulate the level of water in the canal prism, waste weirs, informal overflows, and spillways were used.

'''[[Waste weir]]s''' removed the surges of water from storms or excess when a lock was emptied.<ref name="Kytle p.67">[[#Kytle|Kytle]] p.67</ref> Boards could be removed or added to adjust the amount of water in the level. If one had to empty the whole level for winter, repairs, or emergencies, waste weirs often had paddle valves (similar to those found in locks) at the bottom which could be opened to let the water out.

Waste weirs come in several styles. Originally they were made of concrete masonry with boards on top making a bridge with mules to pass over. A possible example of an old-style waste weir (abandoned) is at 39.49 miles, above Lock 26 (Wood's Lock). Most of these old waste weirs were replaced with concrete structures in 1906.<ref>[[#hahn-towpath|Hahn, Towpath Guide]] p. 75</ref> Another used to be at Pennyfield lock in 1909–1911.

'''Spillways''' are made of concrete, and can be on either side, but if on the towpath side, have a bridge so people (and mules) can cross without getting the feet wet. High water simply flows over the spillway and out of the canal. The longest spillway, near Chain Bridge, is 354 feet long, was made in 1830 (but has been worked on since).<ref>{{cite web |url=http://www.hscl.cr.nps.gov/insidenps/report.asp?STATE=&PARK=&STRUCTURE=&SORT=2&RECORDNO=221 |title=List of Classified Structures |publisher=Hscl.cr.nps.gov |access-date=2016-08-11 |archive-url=https://web.archive.org/web/20161213115444/http://www.hscl.cr.nps.gov/insidenps/report.asp?STATE=&PARK=&STRUCTURE=&SORT=2&RECORDNO=221 |archive-date=2016-12-13 |url-status=dead }}</ref> Another spillway near Foxhall road<ref>{{cite web |url=http://www.hscl.cr.nps.gov/insidenps/report.asp?STATE=&PARK=&STRUCTURE=&SORT=2&RECORDNO=113 |title=List of Classified Structures |publisher=Hscl.cr.nps.gov |date=1979-08-09 |access-date=2016-08-11 |archive-url=https://web.archive.org/web/20161213044907/http://www.hscl.cr.nps.gov/insidenps/report.asp?STATE=&PARK=&STRUCTURE=&SORT=2&RECORDNO=113 |archive-date=2016-12-13 |url-status=dead }}</ref> at mile 1.51, was made in 1835. The spillway and waste weir at Big Pool was built in the 1840s<ref>{{cite web |url=http://www.hscl.cr.nps.gov/insidenps/report.asp?STATE=&PARK=CHOH&STRUCTURE=&SORT=&RECORDNO=724 |archive-url=https://archive.today/20130615065941/http://www.hscl.cr.nps.gov/insidenps/report.asp?STATE=&PARK=CHOH&STRUCTURE=&SORT=&RECORDNO=724 |url-status=dead |archive-date=2013-06-15 |title=List of Classified Structures |publisher=Hscl.cr.nps.gov |date=1979-08-09 |access-date=2016-08-11 }}</ref>

[[image:Informal_Overflow_or_Mule_Drink_on_Chesapeake_and_Ohio_Canal.jpg|thumb|right|200px|An informal overflow. The towpath dips, allowing water to flow over it. Note the boards in the background for people to walk on.]]
An '''informal overflow''' or '''mule drink''' was a dip in the towpath allowing water to flow over, similar to a spillway, but without the bridge or the concrete construction (hence, were more informal). The canalers called these "mule drinks".<ref>[[#Kytle|Kytle]] p. 271</ref> There are documented informal overflows at mileage 10.76, 49.70, and 58.08.<ref>[[#hahn-towpath|Hahn, Towpath Guide]] p. 36, 86, 96</ref> These usually had a drainage ditch which was riprapped with stone to prevent erosion. Historically the towpath dropped two feet to form this overflow.<ref name="Hahn p. 96">[[#hahn-towpath|Hahn, Towpath Guide]] p. 96</ref> Due to silting, construction, etc. many of these overflows are now difficult to find. Hahn states that clues to finding these overflows include: a gully without a culvert, a sudden lowering of the towpath, or the signs of riprap on the towpath or the gully itself.<ref>[[#hahn-towpath|Hahn, Towpath Guide]] p. 86</ref> Many of these (e.g. the one at Pennyfield lock) were replaced by a waste weir.<ref>[http://www.canaltrust.org/quarters/pdf/Pennyfield_Lock_CLI.pdf p. 93] {{webarchive|url=https://web.archive.org/web/20130618224116/http://www.canaltrust.org/quarters/pdf/Pennyfield_Lock_CLI.pdf |date=2013-06-18 }}</ref>