Groundwater Recharge Modeling.
This note discusses approximations of groundwater recharge into Deep Creek Lake. The water in the lake comes from the following mechanisms:
- Direct rainfall on the lake
- Direct runoff, including from stormwater management systems
- Shoreline discharge
- Lacustrine groundwater discharge
It’s the groundwater aspects that will be explored here.
From Ref. 1:
“Groundwater exfiltration into marine systems, is called submarine groundwater discharge (SGD) in the literature and defined as “any and all flow of water on continental margins from the seabed to the coastal ocean, regardless of the fluid composition or driving force”. The freshwater equivalent is called lacustrine groundwater discharge (LGD). LGD includes any and all flow of groundwater from the lakebed to the lake.” In other words: flow from springs at the bottom of the lake and other groundwater flow.
LGD affects the water and nutrient balances of the lake, because surface deposits can materialize in dissolved chemical components in groundwater that can seep deep enough to affect the LGD. The quantification of LGD is challenging and thus often, or perhaps mostly, neglected. References 2-13 address this issue, mostly for coastal areas. I shall not go in detail into the work performed by others, but the references at the end of this report form a starting point for a more exhausting modeling effort, if one so desires.
At Deep Creek Lake this is observed three types of ‘apparent’ recharges taking place:
By the sudden withdrawal of water by the turbines.
Figure 1 is an illustration of this phenomenon. One other explanation is that the generators extract water from a lake at a single location and thereby affecting the lake level gage readings. It can be postulated that an extensive drawdown at a point causes the water level to dip down locally ever so slightly, and because the total lake water mass from far away has to adjust itself to this slight dip, one could postulate that it may take some time to recover. On the other hand, one could also see that recovery would be nearly instantaneous. This requires further investigation, since a quick Google search did not reveal any literature on the subject.
Figure 1. Lake Level and Generator Operation - raw data.
Consider the data span shown in Figure 1. It’s the detailed lake level record starting June 2016, for 5 days. Also shown is when the generators are running. The data is not available directly whether one or both generators are running, but it will be assumed that both are, which is the normal mode of operation. One could go to the Youghiogheny river USGS flow gages and discern what flow rate is coming from the tail race and hence from the generators. One can observe some rise in the lake level after the generators shut down, but it’s not clear by how much because of the noise in the water level gage.
The data shown in Figure 1 is passed through a Loess filter and smoothed with the span factor indicated, with the results shown in Figure 2. One can now see clearly the recharge after shutdown. The overall downslope of the curve suggests very little rainfall during this 5-day period.
Figure 2. Lake Level and Generator Operation - smoothed data.
A recharge rate, by groundwater at the shoreline, during non-rainy periods.
This condition is readily observed in Figure 3, in the early winter time, when the lake is not yet frozen and we haven’t had a long term cold spell. The ground is still warm and hence the groundwater is warm.
This type of groundwater flow is probably quite significant during and shortly after a period of rain. It’s existence is easiest seen in early winter when the lake begins to freeze. One can see all around the lake a region of open water resulting from the inflow of warm groundwater. The photo in Figure 3 demonstrates this effect. This groundwater enters the lake probably over some unquantified depth.
Figure 3. Groundwater Discharge into the Lake at the Shoreline.
Lacustrine Groundwater Discharge - This was described earlier. This is very difficult to pin down. There is a lot of anecdotal evidence that there are a number of springs underwater that feed the lake. People talk about swimming through cold pockets of water that are present all summer. In other words this cold water is probably not inversion water. However, there are ways to identify this type of groundwater. Ref. 14 describes an approach with FO-DTS, Fibre Optic Distributed Temperature Sensing, the same technology that could be used for a river water temperature assessment/model. The buoyancy of warm groundwater during winter and early spring when lake water is colder and heavier than groundwater can be used for identification of groundwater upwelling related hotspots in surface waters. This technique is described in detail in Ref. 15 and 16.
- “From submarine to lacustrine groundwater discharge,” JÖRG LEWANDOWSKI, KARIN MEINIKMANN, FRANZISKA PÖSCHKE, GUNNAR NÜTZMANN & DONALD O. ROSENBERRY
- submarine groundwater discharge
- Phosphorus and Water, USGS
- Phosphorus in a Ground-Water Contaminant Plume Discharging to Ashumet Pond, Cape Cod, Massachusetts, 1999
- Nutrients and toxic contaminants in shallow groundwater along Lake Simcoe urban shorelines
- ESTIMATION OF NATURAL GROUND WATER RECHARGE Amitha Kommadat
- “An Analysis Of Hydrogeology, Groundwater Discharge, And Nutrient Input To Clear Lake”, Dr. William W. Simpkins, Keri B. Drenner, and Sarah Bocchi
- “Phosphorus and Groundwater: Establishing Links Between Agricultural Use and Transport to Streams”, Joseph L Domagalski and Henry Johnson
- “An Introduction to Submarine Groundwater Discharge”, USGS
- “Submarine Groundwater Discharge: An Unseen Yet Potentially Important Coastal Phenomenon”, D. Reide Corbett, William C. Burnett, and Jeffrey P. Chanton
- “Groundwater - the disregarded component in lake water and nutrient budgets. Part 1: effects of groundwater on hydrology,” Donald O. Rosenberry, Jörg Lewandowski Karin Meinikmann and Gunnar Nützmann
- “Phosphorus in groundwater discharge – A potential source for lake eutrophication,” Karin Meinikmann, Michael Hupfer, Jörg Lewandowski
- “Lacustrine groundwater discharge: Combined determination of volumes and spatial patterns,” Karin Meinikmann, Jörg Lewandowski, Gunnar Nützmann
- Upwelling of warm water in lakes due to lacustrine groundwater discharge, Marruedo Arricibita, Amaia I.; Lewandowski, Jörg; Krause, Stefan; Dämpfling, Hauke, April 2016
- Capabilities, limitations and new horizons of Fibre-Optic Distributed Temperature Sensing in ecohydrological and hydrogeological research, Stefan Krause, University of Birmingham,
- Fiber-Optic Distributed Temperature Sensing Technology Demonstration and Evaluation Project, John W. Lane, Jr., USGS, Spring 2006