Lake Hydrology Physics: Observing Shoreline Changes

[Glenstr]

TL;DR Summary

I'm trying to learn more about the physics of hydrology, ie how wind & currents affect lakeshore structure, sand deposits etc.

I live on a lake, and have for almost 3 decades now. Every year I watch shoreline changes, from year to year and shorter timespans, sometimes just days. The lake is large in surface area at 236 km2 (91 sq mi), but with an average depth of only 28' probably relatively small in volume for its size. It also freezes every year with a meter+ ice most years.

Being a northern boreal lake, it's inflow river is fed by a large area of muskeg, which release stored water slowly after spring thaw, this can mean increased flow & increasing lake level well into summer, or some years peaking as early as June, depending on previous winter's snowfall and following rain. Each spring I put in a fixed (non floating) dock in and it's a guessing game where to put it, in close so allow for a foot or more of water level increase, or out far with the chance lake levels increase more than a foot and necessitating a move later in the season (which is what I usually do)

What I find very interesting though, is how wind can affect the shore structure over a matter of weeks or even days. The ice also affects it a lot, depending on prevailing winds when it starts to melt and it's either pushed or pulled into / away from the shore, but it is the wind that has the most dynamic changes.

The shore is very rocky, with some sandy stretches, and it's the sandy stretches that appear and disappear that intrigue me. For example, this year in May (normal ice-off time) the lake was lower than usual and there was a large sandy stretch to the east of our beach area. The lake dropped to quite low levels last summer after an almost record high the year before, and the sandy stretch appeared late in the summer. This was the first time in the 3 decades I have been here that part of the shore was sandy. There was also large sand deposits where there was none before in front of my place, and I thought it might have something to do with a couple of small rock jettys we built to start the dock from.

However. by the time the lake froze last fall the sandy deposit in front of my place was gone, and this spring was still all large (6" to 18" average) rocks. Last week we had about 4 days of strong northwest wind, and now the sandy stretch to the east is completely gone & is all large rocks, the one in front of my place is back, and the shore to my west now has large sand deposits covering most of the rocks. On top of that there is now a long line shaped deposit of 1"- 3" gravel size rocks about a foot above the high water mark for about 100 meters each way.

Prevailing winds on this part of the lake are usually westerly/northwesterly, and the lakeshore is primarily rocky for about 40' from the treeline then all sandy bottom and only about 15-20' deep for almost a kilometer in front of my place.

I find these constant changes all quite fascinating, and different from the mountain lakes I grew up with, and would like to learn more about lake hydrology & how shorelines can be affected, and would like to know if and how much man made structures like small rock jettys can affect the shoreline, since it seems the changes are more pronounced since I built a small one sticking out about 10' about 6 years ago.

Since I couldn't find a suitable hydrology forum anywhere, I though perhaps the Earth Sciences forum might have some folks with expertise in this area. Cheers.

 

[Bystander]

https://books.google.com/books/about/Wind_Waves.html?id=_5ESAQAAIAAJ

 

[Glenstr]

Thanks, I need something to read at night as the days get shorter!

 

[Astronuc]

Perhaps this might be of interest - Incorporating wind sheltering and sediment heat flux into 1-D models of small boreal lakes: a case study with the Canadian Small Lake Model V2.0
https://gmd.copernicus.org/articles/12/3045/2019/

Abstract - Lake models are increasingly being incorporated into global and regional climate and numerical weather prediction systems. Lakes interact with their surroundings through flux exchange at their bottom sediments and with the atmosphere at the surface, and these linkages must be well represented in fully coupled prognostic systems in order to completely elucidate the role of lakes in the climate system. In this study schemes for the inclusion of wind sheltering and sediment heat flux simple enough to be included in any 1-D lake model are presented. Example simulations with the Canadian Small Lake Model show improvements in surface-wind-driven mixing and temperature in summer and a reduction of the bias in the change in heat content under ice compared with a published simulation based on an earlier version of the model.

Maybe one could acquire a copy of the Canadian Small Lake Model and study it. Anything that protrudes into the water and disrupts the flow along the shore would affect the flow of sediment, but I believe it would be a local effect.

 

[256bits]

Summary: I'm trying to learn more about the physics of hydrology, ie how wind & currents affect lakeshore structure, sand deposits etc.

However. by the time the lake froze last fall the sandy deposit in front of my place was gone, and this spring was still all large (6" to 18" average) rocks. Last week we had about 4 days of strong northwest wind, and now the sandy stretch to the east is completely gone & is all large rocks, the one in front of my place is back, and the shore to my west now has large sand deposits covering most of the rocks. On top of that there is now a long line shaped deposit of 1"- 3" gravel size rocks about a foot above the high water mark for about 100 meters each way.

Pacific ocean coastline will have varying coastal deposits winter /summer.
The greater wind in winter produce larger waves which deplete the shore of sand, depositing it somewhat into the sea.
During summer, the more 'gentle' waves will bring the sand back from the ocean to the shore.
It ends up being a back and forth process played out year after year.
You can google 'sand movement winter/summer pacific' to get a bunch of hits.

The sand moves down the shoreline, with the incomming waves not being parallel to the shoreline, but the bashwash does retreat perpendicular to the shoreline.

Peeble beaches are less investigated.