page_title: Chesapeake and Ohio Canal
section_title: Waste weirs, spillways, and informal overflows (mule drinks)
hierarchical_section_title: Chesapeake and Ohio Canal / Locks and engineering / Waste weirs, spillways, and informal overflows (mule drinks)
caption_attribution_description: English: Frame from Down the Old Potomac, illustrating a mule drink or informal overflow, showing boards to walk on as well as the water flowing over towpath.
context_page_description: The Chesapeake and Ohio Canal, abbreviated as the C&O Canal and occasionally called the "Grand Old Ditch," operated from 1831 until 1924 along the Potomac River from Washington, D.C., to Cumberland, Maryland. The canal's principal cargo was coal from the Allegheny Mountains.
  Construction on the 184.5-mile canal began in 1828 and ended in 1850 with the completion of a 50-mile stretch to Cumberland. Rising and falling over an elevation change of 605 feet, it required the construction of 74 canal locks, 11 aqueducts to cross major streams, more than 240 culverts to cross smaller streams, and the 3,118 ft Paw Paw Tunnel. A planned section to the Ohio River at Pittsburgh was never built.
  The canal way is now maintained as the Chesapeake and Ohio Canal National Historical Park, with a trail that follows the old towpath.
context_section_description: To regulate the level of water in the canal prism, waste weirs, informal overflows, and spillways were used.
  Waste weirs removed the surges of water from storms or excess when a lock was emptied. 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. 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). Another spillway near Foxhall road at mile 1.51, was made in 1835. The spillway and waste weir at Big Pool was built in the 1840s
  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". There are documented informal overflows at mileage 10.76, 49.70, and 58.08. These usually had a drainage ditch which was riprapped with stone to prevent erosion. Historically the towpath dropped two feet to form this overflow. 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. Many of these (e.g. the one at Pennyfield lock) were replaced by a waste weir.
caption: An informal overflow. The towpath dips, allowing water to flow over it. Note the boards in the background for people to walk on.
exif: {}