June 2010 monitoring

It is definitely summer! Although it’s forecast to be in the mid 90s today, we were able to monitor early enough that it was only 27 C / 80 F (though it  felt warmer). The water temp was 26.

It’s amazing how much the water has receded since the 3.3″ fell 10 days ago – it’s back to the usual mild stream with only a couple of indications that it had recently been a raging torrent. Two changes in particular we noted were that the south bank adjacent to the bridge (between the bridge and sample site) was eroded – see the February photo for a comparison. And there is now a big tree in the middle of the stream just beyond the sample site (photo).

It felt a bit strange, knowing that we were working in the area which 10 days earlier was covered by rushing water.  As we worked the pigeons  nesting under the bridge cooed encouragement.

Upstream from the bridge the waterfall was back to its placid flow – a couple of birds were cooling their toes in it. And above that the stream was again low and slow.  There were several fairly large schools of minnows swimming around.  The underwater algae is growing though still just in clumps. Looking back at May’s photos, it has spread – there are more clumps and they are a bit longer, but not yet long enough to flow downstream.

Measurements…I found last year’s data sheet, and it’s interesting to see how the two sets compare. Last year this time we were in a stage 3 or 4 drought (4 is the worst possible stage).

• Air/water temps were close – now 27/26 (C), last year 30/26.
• The specific conductance is 660 now, last year it was 560.
• pH is 7.0 for both years. This year it was barely 7.0, maybe closer to 6.9 (see the photo).
• The biggest difference is in the dissolved oxygen. This year it is 4.3 – lower than last month but not surprising given the warmer water. Last year it was only 2.2 at the same water temperature. Last year the flow was low compared to this year’s normal, so that may also have an influence, along with the lack of rain.
• The e-coli was much higher than we’ve ever seen it, but that’s probably to be expected for this urban stream, given the flood with a huge amount of runoff from streets and yards (many of which probably have pet waste). The fine folks at LCRA can comment more on that.

It will be interesting to see how the algae and other measurements change over the summer.

view of the sample site from the north bank

view from the north bank of the sample site and the bridge

view of the crossing rocks, sample site & downstream

view from bank of stream between crossing rocks & under bridge

downstream view of crossing rocks and site from bridge

new big tree in stream beyond sample site since last week’s flood

south bank by bridge after flood shows signs of erosion

the water under the bridge is back to its low “normal” level

view upstream from the sewer inflow area

the dissolved oxygen is lower so the color is a lighter gold than during the cooler months

pH is barely 7-0 – lower than usual

looking downstream to bridge

an orange traffic cone, carried by the floodwaters, found a resting place just before the sewer pipe entrance to the creek.

stream adjacent to the upstream side of the bridge

vegetation under bridge again is nowhere near the water

view just upstream of bridge

the waterfall and downstream

birds enjoying the quiet waterfall

looking upstream above the waterfall

still an impressive flow from the sewer above the bridge.

further upstream the water is its normal level

many small fish are upstream of bridge

upstream of bridge, underwater algae is growing

low enough water upstream that some rocks are exposed