April 2018

April 15, 2018 – a beautiful, cool, sunny day. The good news: no more dead fish, as we saw last month (cause: a water main break upstream, flooding the stream with much treated – chlorinated – drinking water. Chlorine can kill fish, and it did.). The dissolved oxygen is back to normal for this time of the year, 6.7. I’m sure the fish are happy about that. The stream is also again very clear, unlike last month, when everything thing was unusual in a bad way.

The aquatic life is recovering, we saw a few gambusia (minnows), both a handful of regular size and more babies. Also saw a small turtle by the sample site. Again, no pigeons or other birds. (When pigeons roost under the bridge, their droppings can increase the e-coli bacteria.)

Overall, the stream looked healthier than last month. There is noticeably more algae, both surface and submerged. Last month most of the algae was a gray-green color. This month it’s all green, and the submerged algae is composed mostly of many long strands.

A big change is the wide gravel bar that has existed under and just downstream of the bridge for months is gone. Now the stream has a significantly wider area to flow through the trail crossing. Guess there was enough rain and water in the stream to move all that around. Looks like someone placed some flat rocks in the trail crossing area to allow people to cross with dry feet.

Stream flow and depth: The waterfall has a good flow across about 1/3-1/2 of its width. just above the bridge it was lower than we’ve seen it for a while, it was possible to cross to the other side with dry feet if you have long legs. Upstream of the waterfall and dry inlet, the “sometime island” rocks were dry. And the upstream bridge column was mostly dry, with a couple of puddles nearby.

A hydro geologist friend joined us and had some interesting observations. He noted that millions of years ago this area was at the bottom of the ocean (which I already knew) and that due to the depth of the ocean and hence the lack of light, there was very little aquatic life. As fish, etc. died their bodies would sink and decompose; he had (elsewhere in this area) found a shark’s tooth.

This area is comprised mostly of Austin Chalk, which blends into Eagle Ford formation. Upstream of the waterfall, he pointed out a horizontal strip of rock sandwiched between the lighter Austin Chalk above and below. And he also explained the effect that currents and waves can have on rocks, pointing out the wave effect in the rocks (below). Next to that he showed me a small inoceramus clam (Wikipedia link) fossil imprint.

Observations:

Air temp: 15 C (59 F)
water temp 14.5 C (58.1 F)
dissolved oxygen 6.7 (65%)
pH 7.0
nitrates 0.3
specific conductance 520
E-coli 3 ML samples: about 133 colonies, good for an urban stream

sample site from north bank

downstream view from under bridge

stream under bridge from north bank

trail crossing area

closeup of trail crossing area

trail crossing stream flow

under bridge

under bridge-3 columns in water

upstream column and low stream

stream from culvert to under bridge

stream view from above culvert

upstream view from under bridge

waterfall with much algae

waterfall closeup-algae

waterfall area

waterfall and upstream

upstream of waterfall with dry inlet

submerged algae near inlet

much submerged algae above waterfall

dry sometime island rocks

downstream view from above inlet

dark rocks area-Eagle Ford

wave in rocks from ocean currents

inoceramus clam fossil in rocks

dissolved oxygen 6-7