Gage Location Specifications

Gage Installations - Location Specifications and Considerations for Upgrades

General Guidelines

FOR EACH LOCATION KEEP IN MIND:

Accessibility

• Ease of access to transmitter box to change batteries or remove for troubleshooting or repair.

Theft and Tampering

• This hasn’t been a significant problem, but something to keep in mind.
• Our strategy has been to label prominently and to make removal require intention

Safety

• The transmitter box must be able to be accessed safely.
• Some sites are in inherently dangerous locations especially during flooding (minimize additional potential hazards i.e. use of ladders, heavy swinging arms that don't have breaking winch, having to stand on edge of steep drop offs, etc.).

Data Reliability

• Sensor must be at same exact height in exact same position each time it is raised and lowered.

• Sensor must be perpendicular to ground.

• If on a cantilevered arm that raises and lowers, the arm must be level and static when raised.
• We must be able to accurately measure the height of the sensor over the local benchmark elevation. The height will be measured on initial install and then once or twice a year for verification.

Flood Height

• Sensors must be mounted above 60’ flood level.

• The USGS Carnation gage recorded 60’ flood was ~4.5’ higher than the Oct 22, 2019 flood.

• See Table 1. for sensor mounting height requirements.

Table 1. Sensor Height Requirements for Maximum Flood Levels

Gage Location	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, May-2020)	New Sensor Height Requirements (ft above ground)
SVPA-37 SE Fish Hatchery Road at Snoqualmie Falls Golf Course	99.06	unknown - not running during flood			11.31	>11.31
SVPA-34 W Snoqualmie River Rd SE at the “T”	81.69	80.47	84.97	-3.28	7.98	12.48
SVPA-34 Snoqualmie River at Keller Dairy	90.68	85.84	90.34	0.34	20	20
SVPA-26 W Snoqualmie River Rd NE at the Blue Heron Golf Course	74.32	73.46 (max pre-crest, sensor taken down due to flood levels approaching sensor)	77.96	-3.64	11.3	>15.8
Snoqualmie River at the Tolt Bridge	not installed	unknown	unknown	n/a	n/a	height of bridge guard rail adequate
SVPA-22 Snoqualmie River at Stossel Bridge	not installed	57.96	62.46	n/a	n/a	height of bridge guard rail adequate
SVPA-17 NE 100th St at Goose and Gander Farm	54.24	53.81	58.31	-4.07	8.19	12.69
SVPA-15 124th St East at Local Roots Farm	55.45	46.96	51.46	3.99	15.04	15.04
124th St West	not installed	estimate based on photos and 124th E	unknown	n/a	n/a	TBD
SVPA-12NE 138th St at Wild Canary Farm	47.9	45.26	49.76	-1.86	12.3	14.5

Device Consideration

Antennas

• Must be mounted directly on transmitter box and cannot be extended.

Transmitters

• Mount transmitter as high as possible to improve line of sight and RSSI.
• Must be easily accessible from the ground or using a short ladder.
• Can be mounted separate from sensor.
• Cannot become submerged during flooding.

Sensors

• Can be mounted separate from transmitter.
• Cannot be mounted higher than the range of sensor (30’ sensor: 30’, 14’ sensor: 14’)
• Come with 6’ cable - can be cut.
• Can be ordered with longer cables (15 – 200').
• Will not give accurate readings if flood waters are within 10” of the sensor face.
• Can be submerged during flooding BUT, will not give accurate readings.
• Must be mounted directly over center of ditch/concrete pad.

Sensor Cone

• Emits an ultrasonic pulse with a 15° sensing cone.
• The higher the sensor, the larger the diameter of the sensing cone at the ground/water surface.
• Be sure the sensor is extended far enough from the mounting pole to not sense it.
• 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

GAGE LOCATIONS:

1. W Snoqualmie River Rd NE at the Blue Heron Golf Course

Problems and Considerations:

• Sensor Height – mount > 15.8' above surface water in ditch.
  • Cantilever arm must be level and static.
  • Mount over center of ditch.
  • Could use tree behind existing post to get sensor up higher.
• RSSI issues – mount antenna higher for better RSSI, site is furthest away from receiver, has connection problems.
• Access issues – required height of sensor and position of ditch makes access difficult with a ladder.
  • Must be able to access transmitter on foot, or using a short ladder.

2. 124^th St East at Local Roots Farm

Problems and Considerations:

• Sensor Height – mount at same height or greater (15.04’).
  • Cantilever arm must be level and static.
  • 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.
  • Cannot reach transmitter to change batteries without taking the post down, shouldn't have to take post down to access transmitter.
  • Position of post adjacent to the ditch is awkward and unsafe when using a ladder to try and access sensor.
  • Could move the location closer to 124^th St for better vehicle access.

• Sensing Cone Issues – the cone of detection is very wide at the ground level.
  • Be sure sensor mounted out from the post by at least 24” (radius of cone at ground level).
  • Problems with flood debris getting caught on post and being detected within the cone even after flood waters recede.

3. NE 138^th 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)
  • Mount out over center of ditch.
  • Cantilever arm must be level and static.
  • 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.
  • Mount transmitter and antenna as high as possible (use existing telephone pole?)
  • Mount transmitter and sensor separately.
  • Use 30’ sensor with longer cable.

• Access issues – location is immediately adjacent to gravel road, but height poses problem.
  • 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.
  • Sensor should be mounted at minimum height requirements to minimize size of cone.
  • Vegetation will need to be cut back extensively along ditch edges.
  • 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.
  • 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.
  • This is the lowest part of the road, so it should be installed in the same location.
  • Theft worries?

• Sensing Cone Issues – the cone of detection will be wider with the new height.
• Be sure sensor mounted out from the post by at least 20.5” (radius of cone at ground level).
• Be sure road edge is not within cone.
• 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’).
  • Cantilever arm must be level and static.
  • Unsure of 60’ flood height at this location.
  • 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.
  • Mount transmitter and antenna as high as possible (use existing telephone pole?)
  • Mount transmitter and sensor separately.
  • Use 30’ sensor with longer cable.

• Access issues – location is immediately adjacent to parking lot, but height and position over ditch poses problem.
  • Transmitter is virtually inaccessible as it is now.
  • If transmitter is mounted separate from sensor, both will need to still be accessible for battery changes, maintenance.
  • 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.
  • Sensor should be mounted at minimum height requirements to minimize size of cone.
  • Vegetation (knotweed) will need to be maintained.
  • 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’).
  • Cantilever arm must be level and static.

• RSSI issues – receiver is nearby, but leaf cover may be blocking line of sight.
  • Could try to get antenna out over river further or up higher.
  • Could mount transmitter and sensor separately.

• Safety Issues – location has a steep (~10’) drop off into the river.
  • Design must take into account river safety and ease of access of transmitter.

• Access issues – location is immediately adjacent to road, but in a precarious spot at edge of bank.
  • 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.
  • Any interfering branches may need to be removed.
  • Sensor should be mounted out over the river as far as it is now or farther.

7. NE 100^th St at Goose and Gander Farm

Problems and Considerations:

• Sensor Height – mount at least 12.69’ above concrete pad.
  • Cantilever arm must be level and static.
  • 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.  
  • 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.
  • Sensor should be mounted out (> 21”) away from post (radius of cone).

8. 124^th 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