[Tagging] Spillways

John Willis johnw at mac.com
Wed Mar 22 06:49:55 UTC 2017

> On Mar 22, 2017, at 3:15 PM, Bill Ricker <bill.n1vux at gmail.com> wrote:
> ​or use surface tags to distinguish the paved from unpaved​ as we do with roads ?

This section is paved, but it is the function of the wall of dirt with asphalt on top I’m trying to map. 

someone actually took a picture out there in the winter.  https://goo.gl/maps/QfrZfUiVze22 <https://goo.gl/maps/QfrZfUiVze22> 

The old way (beyond the gate) disappears, as the top of the old levee was removed, lowering it by 3-5m. https://goo.gl/maps/bTdcVV6H9pn <https://goo.gl/maps/bTdcVV6H9pn> . This is covered by asphalt (to protect against erosion), and it is an embankment (holding back water during flooding), but it’s function is a spillway. the river to the right is the path to the sea. The entire inner reservoir (way off to the left) has concrete walls. Wether is is concrete, asphalt, or earth, it could be a dam, a spillway (with/without control gates), or an emergency spillway, if the normal one is in danger of being overtopped. in this case, the emergency spillways protect the gates to the south and the homes to the west. if you pan the photo 180 degrees (look behind “you”), you can see the gates it is protecting. 

The dam and a weir have the same job - to hold back water. a weir usually holds back water to feed into a pipe or some other use for the water, as a dam does, but is designed to be overtopped. it is often submerged, being overtopped, while doing it’s main function of routing water into a pipe or making a lake or similar.
a spillway's sole job is to get rid of excess water, for the safety or planning the use of the dam’s capacity. it is a feature of the dam (or other water control system), not the main feature itself. in this case, the spillway is a part of the levee system.

waterway=spillway + emergency=yes, + surface=* as the spillway is for emergencies seems appropriate. 

Thanks for the feedback. 


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