[Juniper LeiferParticipant]

Hi All,

Keep an eye on the physical changes around your sensors.

I sent this video out via email earlier to seek some advice about adjusting the placement of our sensors to adapt to obvious changes in the shape of the streambed.  Dave reminded me that it might be useful to share the conversation with the group as there will likely be others facing similar challenges.

As you can see in the video – my sensors are buried and there is a clear change in the shape of the streambed.  The bottom of the stream is now up to about 13cm on the staff gauge.

In addition to interfering with data collection, this reduces the accuracy of any rating curves based on an outdated mapping of the cross section.

Discuss…

(The video file is too large to be cooperative but I’m hoping this attached clip makes it through…)

 

Attachments:

1. buried-sensors-clip_1_1_1.mp4

[Juniper LeiferParticipant]

The video is too big – I am going to try to cut it down….

Update: Okay – so maybe no video…

 

[David BresslerParticipant]

Juniper,

Heather Brooks is working on a fix for this.  How large is your video file?

[Juniper LeiferParticipant]

I think I managed to finally get it attached to the original post after I had all but given up.  Someone tightened it up for me somehow.

[David BresslerParticipant]

Heather was going to make some adjustments to the site.  As we use the site more we’ll probably be able to articulate and improve these types of things.

Regarding the initial question on the filling in of the streambed around the sensors.  It looks like it’s not the type of situation where you would be able to dig out the sensors every now and again – that is, it seems like the whole stream bed in that location has filled in.  If this is correct Juniper, then I think it will be good for you and Christa Reeves (and maybe Jim Braski) to move the sensors up.  You’ll want to make sure to do it at baseflow and you’ll also want to make sure to note the sensor depth before and then after re-positioning.   The staff gauge is filled in too, so you’ll want to reposition it too,  again making sure to record staff gauge depth before and after.

To document this type of problem it would also be great if you could take underwater before and after photos of the staff gauge and the sensor bundle.  And of course normal above water photos of the station and the stream will be good.  Then you can post the photos here.

The other thing to consider here is that the channel itself may have changed enough due to all the sediment filling that it may warrant re-doing the channel cross section, i.e., re-delineating the shape of the channel.  As you know this is for purposes of modeling/predicting cross sectional wetted area to be used along with velocity measurements to calculate discharge, to then be incorporated into the rating curve (depth versus discharge).  The ability to model the wetted cross sectional area is particularly useful when the water is too high to do the measurements by hand (i.e., too high to wade in the stream and measure the wetted cross sectional area).

The before and after sensor and staff gauge measurements will then be used to adjust the rating curve for this site (via this site’s rating curve calculator spreadsheet).

 

 

[Juniper LeiferParticipant]

Yes, I agree.  The sensors are hopelessly buried and there is no way to keep them clear.  Digging it out is only a momentary fix, the free space fills in quickly.  This will require a relocation of the sensors to raise them as per your suggestion.  We will not generate good and accurate data until we can pull the sensors up.  We will definitely need to remap the cross section accordingly.

Questions:

Is this something we should aim to do now or that we should hold off until spring for?  I would love to get our data up and running asap but I’m wondering if installing or reinstalling equipment ahead of any winter freeze is a risk or a challenge.

Yesterday – the streambed seemed to be up even higher on the staff gauge – up to around 15cm.  Is there anything outside of the standard flashiness of the stream that might be sending all of this sand downstream? I imagine the shape of the channel to be an ever evolving thing – just wondering if this sudden change is consistent with anything else I should be paying attention to.

Right now – I’m at a standstill.  Do you suggest we move the sensors right away?

[David BresslerParticipant]

I think if Christa Reeves can get out there to help, both moving the sensors up and doing the cross section could be done soon.  Juniper, you and all your other people who are involved with managing the station should try to be there with Christa so that it can serve as a training in this hardware management topic area.

As mentioned before, underwater photos and regular photos of before and after will be very useful.  Also recording sensor depth and staff gauge depth before and after are extremely important.

It’s a good question about the extra sediment.  This is happening at other stations (UT to Pike Creek and Pike Creek at The Independence School in Delaware; Ridley Creek, Pickering Creek).  The sensors force us to look at the stream bed and then we notice how it’s changing.  It’s hard to say definitely what’s happening but it sure seems to me that it’s related to the excessive and extreme rains we’ve had this year.  This anecdotal and visual evidence of the amount of sediment at the sensor stations is a coarse representation of what some folks are doing with the data once the discharge/sensor depth and turb/tss rating curves are developed – i.e., quantifying the amount of sediment moving during storms.

My assumption right now is that the excessive storm flow is:

1. washing more sediment off exposed areas of the landscape into the stream
2. further eroding existing exposed banks, and
3. ripping out trees and vegetation and creating more exposed banks.

So the heavy precipitation this year and it’s apparent effects point to the increasing need to address the issues of:

1. exposed soil wherever it may be located (on land at construction sites, agricultural fields, etc. or in-stream) and
2. quick and “flashy” runoff from impervious surfaces (e.g., parking lots, roads, residential, commercial, industrial areas) which creates powerful stream flows that
   • rip out trees and vegetation exposing more loose soil to stream flow,
   • scour existing exposed stream banks adding more sediment to the stream, and
   • scour the stream bottom exposing and mobilizing more sediment

So Juniper, the question for you is what’s happening up stream and what can be done about it?

 

 

 

 

[David BresslerParticipant]

Christa, Juniper,
<div>Have you two managed to coordinate on this?  It might not be suitable right now with the weather but would be good to try to get something planned.  Moving the sensors up should presumably just be loosening the hose clamp and shifting them up (documenting before and after depths) – that is assuming there is enough room on the stake/pvc.  Same for staff gauge – loosen brackets and move it up (again documenting before and after).  When you redo the cross section you can use the same location and string the line level and measuring tape between the two right and left bank rebars.  You’ll use the attached sheet (CrossSectionDischargeForm_v7.xlsx) to record the data when mapping out the new cross section.  Method for the cross section work is located in Section “Predicting Discharge in Unwadeable Conditions” of the manual appendices: https://www.envirodiy.org/mayfly-sensor-station-manual/appendices/measuring-discharge/</div>

Attachments:

1. CrossSectionDischargeForm_v7.xlsx

[Anonymous]

Hey Juniper,

I am available to get out there with you and get your equipment moved, I am seeing similar situations play out on other systems (most recently on the Little Lehigh). It has definitely been a high precipitation year and along with that an increase in sediment. Let me know when you are available.

Thanks,

Christa

[Juniper LeiferParticipant]

Thanks Christa.  I am nearby the station and can easily get out there to meet you at some point when you are available.  Email me a few upcoming days and times that work for you and I will let you know which is best.  We should at least get out there and take a good look at what is going on so that we can assess if we want to try and make an adjustment now or if we need to hold out for warmer weather.  I’m not sure we’ll have enough room to raise the sensors on the existing equipment.   The changes seem to be ongoing – the streambed appears a bit higher at every visit.

David – the streambed is changing as it fills in with sand.  I imagine that sand like this, deep in some areas, would continue to move around the channel changing the shape with every passing storm.  Might this be an ongoing problem?

[Author]

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