Gage Location Specifications
Flood Sensor/Transmitter Installation Upgrades
| Sensor
Either 14’ or 30’ range |
| Sensor Cable (6’)
Can order longer cables if needed |
| Transmitter Box |
| Mounting Bracket
Sensor and transmitter can be removed from this and mounted separately |
Figure 1. Senix Sensor and Transmitter with Mounting Bracket
The following listed sensor/transmitter installations need to be revamped keeping in mind:
· Accessibility
o Ease of access to transmitter box to change batteries or remove for troubleshooting or repair.
· Theft and Tampering
o This hasn’t been a significant problem, but something to keep in mind.
· Data Reliability
o Sensor must be at same exact height in exact same position each time it is raised and lowered.
o Sensor must be perpendicular to ground.
o If on a cantilevered arm that raises and lowers, the arm must be level and static when raised.
· Flood Height
o Sensors must be mounted above 60’ flood level.
o The USGS Carnation gage recorded 60’ flood was ~4.5’ higher than the Oct 22, 2019 flood.
o See Table 1. for sensor mounting height requirements.
Table 1. Sensor Height Requirements for Maximum Flood Levels
| Site | Current Sensor Height (ft ASL) | Oct 22nd Flood Crest (ft ASL) | Estimated 60' Flood Crest (ft ASL) | Distance of 60' Flood from Sensor (ft) | Current Sensor Height (ft above ground) | New Sensor Height Requirements (ft above ground) |
| Sno Falls Golf Course | 99.06 | unk | 11.31 | >11.31 | ||
| The "T" | 81.69 | 80.47 | 84.97 | -3.28 | 7.98 | 12.48 |
| Keller Dairy | 90.68 | 85.84 | 90.34 | 0.34 | 20 | 20 |
| Blue Heron Golf Course | 74.32 | 73.46 | 77.96 | -3.64 | 11.3 | 15.8 |
| Tolt Bridge | Not installed | unknown | unknown | Bridge Guard Rail Adequate | ||
| Stossel Bridge | Not installed | 57.96 | 62.46 | Bridge Guard Rail Adequate | ||
| Goose and Gander | 54.24 | 53.81 | 58.31 | -4.07 | 8.19 | 12.69 |
| 124th East at Local Roots | 55.45 | 46.96 | 51.46 | 3.99 | 15.04 | 15.04 |
| 124th West | Not installed | TBD | ||||
| Wild Canary Farm | 47.9 | 45.26 | 49.76 | -1.86 | 12.3 | 14.5 |
· Antennas
o Must be mounted directly on transmitter box and cannot be extended.
· Transmitters
o Mount transmitter as high as possible to improve line of sight and RSSI.
o Must be easily accessible from the ground or using a short ladder.
o Can be mounted separate from sensor.
o Cannot become submerged during flooding.
· Sensors
o Can be mounted separate from transmitter.
o Cannot be mounted higher than the range of sensor (30’ sensor: 30’, 14’ sensor: 14’)
o Come with 6’ cable - can be cut.
o Can be ordered with longer cables (15 – 200 ft).
o Will not give accurate readings if flood waters are within 10” of the sensor face.
o Can be submerged during flooding BUT, will not give accurate readings.
o Must be mounted directly over center of ditch/concrete pad.
· Sensor Cone
o Emits an ultrasonic pulse with a 15° sensing cone.
o The higher the sensor, the larger the diameter of the sensing cone at the ground/water surface.
o Be sure the sensor is extended far enough from the mounting pole to not sense it.
o See Table 2. For cone diameters
Table 2. Ultrasonic Cone Diameters at Varying Heights
| Distance from Sensor (ft) | Diameter of Cone (in) | Diameter of Cone (ft) |
| 1 | 3.15 | 0.26 |
| 2 | 6.32 | 0.53 |
| 3 | 9.47 | 0.79 |
| 4 | 12.64 | 1.05 |
| 5 | 15.79 | 1.32 |
| 6 | 18.96 | 1.58 |
| 7 | 22.11 | 1.84 |
| 8 | 25.27 | 2.11 |
| 9 | 28.43 | 2.37 |
| 10 | 31.59 | 2.63 |
| 11 | 34.75 | 2.90 |
| 12 | 37.91 | 3.16 |
| 13 | 41.07 | 3.42 |
| 14 | 44.23 | 3.69 |
| 15 | 47.39 | 3.95 |
| 16 | 50.55 | 4.21 |
| 17 | 53.71 | 4.48 |
| 18 | 56.87 | 4.74 |
| 19 | 60.02 | 5.00 |
| 20 | 63.18 | 5.27 |
| 21 | 66.34 | 5.53 |
| 22 | 69.50 | 5.79 |
| 23 | 72.66 | 6.06 |
| 24 | 75.82 | 6.32 |
| 25 | 78.98 | 6.58 |
| 26 | 82.14 | 6.84 |
| 27 | 85.30 | 7.11 |
| 28 | 88.46 | 7.37 |
| 29 | 91.62 | 7.63 |
| 30 | 94.78 | 7.90 |
1. W Snoqualmie River Rd NE at the Blue Heron Golf Course
Problems and Considerations:
· Sensor Height – mount > 15.8 ft above surface water in ditch, and directly over center.
· RSSI issues – mount antenna higher for better RSSI, furthest away from receiver, has connection problems.
· Access issues – required height of sensor and position of ditch makes access difficult with a ladder.
· Could use tree behind existing post to get sensor up higher.
2. 124th St East at Local Roots Farm
Problems and Considerations:
· Sensor Height – mount at same height or greater (15.04’).
o Cantilever arm must be level and static.
o Mount out over center of ditch if possible.
· RSSI issues – must be kept at same height for best RSSI.
· Access issues – field adjacent to ditch is often saturated, access to site by foot.
o Cannot reach transmitter to change batteries without taking the post down, because of its position in the ditch.
o Could move the location closer to 124th St for better vehicle access.
· Sensing Cone Issues – the cone of detection is very wide at the ground level.
o Be sure sensor mounted out from the post by at least 24” (radius of cone at ground level).
3. NE 138th St at Wild Canary Farm
Problems and Considerations:
· Sensor Height – mount at least 14.5’ above bottom of ditch (must be > 2’ higher than current)
o Mount out over center of ditch.
o Cantilever arm must be level and static.
o Sensor should be moved from NNW to more of a NW orientation to be directly over the ditch to get the best possible readings.
· RSSI issues – poor RSSI since this location is farthest from receiver and is in a topographic hole.
o Mount transmitter and antenna as high as possible (use existing telephone pole?)
o Mount transmitter and sensor separately.
o Use 30’ sensor with longer cable.
· Access issues – location is immediately adjacent to gravel road, but height poses problem.
o If transmitter is mounted separate from sensor, both will need to still be accessible for battery changes, maintenance.
· Sensing Cone Issues – the cone of detection is very wide at the ground level.
o Sensor should be mounted at minimum height requirements to minimize size of cone.
o Vegetation will need to be cut back extensively along ditch edges.
o Sensing cone least 44.23” (diameter of cone at ground level).
4. W Snoqualmie River Rd SE at the “T”
Problems and Considerations:
· Sensor Height – mount at 12.48’ above bottom of ditch.
o Currently the only site using a 14’ sensor – do not mount higher than 14’.
· Access issues – location is immediately adjacent to road but will be raised up higher.
o This is the lowest part of the road, so it should be installed in the same location.
o Theft worries?
· Sensing Cone Issues – the cone of detection will be wider with the new height.
o Be sure sensor mounted out from the post by at least 20.5” (radius of cone at ground level).
o Be sure road edge is not within cone.
o May need to install post back from ditch
5. SE Fish Hatchery Road at Snoqualmie Falls Golf Course
Problems and Considerations:
· Sensor Height – mount at current height or higher (> 11.31’).
o Cantilever arm must be level and static.
o Unsure of 60’ flood height at this location.
o Currently sensing concrete wall, mount out over edge of concrete pad for best readings.
· RSSI issues – Removed indoor receiver from this location. poor RSSI since this location is far from receiver.
o Mount transmitter and antenna as high as possible (use existing telephone pole?)
o Mount transmitter and sensor separately.
o Use 30’ sensor with longer cable.
· Access issues – location is immediately adjacent to parking lot, but height and position over ditch poses problem.
o Transmitter is virtually inaccessible as it is now.
o If transmitter is mounted separate from sensor, both will need to still be accessible for battery changes, maintenance.
o Ladder will not fit in concrete pad below sensor – spread too wide.
· Sensing Cone Issues – the cone of detection is very wide at the ground level.
o Sensor should be mounted at minimum height requirements to minimize size of cone.
o Vegetation (knotweed) will need to be maintained.
o Sensing cone least 37.91” (diameter of cone at ground level).
6. Snoqualmie River at Keller Dairy
Problems and Considerations:
· Sensor Height – mount at current height (20’).
o Cantilever arm must be level and static.
· RSSI issues – receiver is nearby, but leaf cover may be blocking line of sight.
o Could try to get antenna out over river further or up higher.
o Could mount transmitter and sensor separately.
· Safety Issues – location has a steep (~10’) drop off into the river.
o Design must take into account river safety and ease of access of transmitter.
o SVPA owns harness and rope if needed for access.
· Access issues – location is immediately adjacent to road, but in a precarious spot at edge of bank.
o If transmitter is mounted separate from sensor, both will need to still be accessible for battery changes, maintenance.
· Sensing Cone Issues – the cone of detection is very wide at water surface.
o Any interfering branches may need to be removed.
o Sensor should be mounted out over the river as far as it is now or farther.
7. NE 100th St at Goose and Gander Farm
Problems and Considerations:
· Sensor Height – mount at least 12.69’ above concrete pad.
o Cantilever arm must be level and static.
o This site could use a 14’ sensor if it is repaired.
· Access issues – location is immediately adjacent to farm access road, but may not be useable to access.
o Will need ladder or some way to access transmitter for battery changes, maintenance.
· Sensing Cone Issues – the cone of detection will be wider since the sensor will be higher than is currently.
o Sensor should be mounted out (> 21”) away from post (radius of cone).
8. 124th St West – Location TBD (47.709092, -122.002502)
Considerations:
· Needs to be constructed in the KC right of way, over the ditch.
· Find the low spot in the road using survey data for better placement.
· Height TBD based on estimated flood height here.
· Will need a design that is easy to access without a ladder since there is no parking to bring a ladder and it’s right next to a busy street.
BRIDGE INSTALLS
9. Stossel Bridge
10. Tolt Bridge
