the exception of short levels, almost every level had a waste weir between the locks. At locks, there was often a bypass weir which fed water to the flume, allowing water to bypass the lock into the lower pound. This could be adjusted, similar to the waste weir by adding or removing boards to control the water level. Spillways and informal overflows (mule drinks) Spillways were also used, allowing the water to spill over and into the surrounding rivers. These may be positioned over the towpath or on the berm side of the canal. An "informal overflow" on American canals is a dip in the towpath which functions as a spillway, but usually lacking concrete or formal structure. The boatmen sometimes called these "mule drinks", since the mules would drink from the water flowing over the towpath. Informal overflows were often replaced by a waste weir or lined with concrete or masonry to make a more "permanent" spillway. Stop gates If the pound was many miles long, sometimes the canal would be designed with stop gates, so that if there was a break in the canal the whole pound would not lose all its water. Isolating the break would allow the company to make repairs sooner. For instance, on the 14 mile level of the Chesapeake and Ohio canal, there were stop gates put before and after Big Pool so that it (the Big Pool lake) would not have to be drained in case of breaks or repairs. Animal escape On the Erie Canal, in the three mile long rock cut above Lockport, if a mule or horse fell into the canal pound, there were some escape "holes" cut in the towpath, a depression covered over by wooden boards, so that the animal could go into the "hole" and then be rescued. This was as a result of the bank being practically vertical, making it impossible to retrieve one that fell into the canal. Ramps at the side of canals next to the towpath are quite common in England particularly where horses were known to fall in. For example there is one on the Hanwell Lock Flight of locks on the Grand Union Canal. Sand bars and obstructions Canal levels sometimes have sand bars or shallow areas where the boat will get stuck. It is common on English canals for boaters to carry a barge pole to help punt the