Reservoirs & Lakes

[anonymous1]

I'm having trouble representing large lakes and man-made reservoirs in my model. Could anyone provide some tips on how to properly implement these?

[jrcraig]

Some recommendations for handling reservoirs and lakes:
(1) Make sure that the stage-volume, stage-area, and stage-discharge curves in the :Reservoir command cover the entire range of possible stages. In particular, if the reservoir is always running at very low flows, you will want to add some data points where the volume is non-zero but the flow is zero, i.e., for simulating when the water storage is below the outlet elevation.

(2) Check your area-volume relations - generally, it is a good rule of thumb to keep the area relatively constant. It is only used in ET calculations on the reservoir mass balance. If the Area is constant with stage, the volume increments should be roughly equal, i.e., dV=dh*A, where the stage increments dh have to be even as required by Raven. Generally, there is very little benefit to getting the A vs. h relation right, but the V vs. h and Q vs. h relationships are critical. Areas and volumes should *always* be monotonically increasing with stage.

(3) For small reservoirs, (those that are ~<5% of the total basin area, do not bother linking the reservoir to an HRU (i.e., do not fill out the :HRUID command in the :Reservoir-:EndReservoir block). The mass balance on the reservoir is then simply dS/dt=Qin-Qout, where the on-reservoir precipitation is implicitly included in the Qin, and the from-reservoir evaporation is effectively ignored.

(4) For large lakes and reservoirs, especially those with multiple upstream subbasins draining to them, it is useful to assign the entire subbasin to be a LAKE-type HRU, and link the HRU to the reservoir using the :HRUID command. For these large reservoirs, the mass balance is then calculated as dS/dt=Qin-Qout-E*A, where again precipitation on the lake is implicitly included in the Qin term.

(5) In all cases, if you are using a LAKE soil profile for the reservoir/Lake HRU, the precipitation on the lake will be assigned to the state variable indicated by the :LakeStorage command in the .rvi file (by default, SURFACE_WATER). Note that if your lake storage variable is anything other than SURFACE_WATER (e.g., a conceptual store represented as a SOIL[] state variable), the storage will have to be flushed to surface water with a :Flush command in the :HydrologicProcesses block or another process which can move water from the lake storage to surface water. Otherwise, the lake storage will only accumulate.

(6) The reservoir HRU centroid is used for estimation of precipitation and evaporation rates over the lake.

[anonymous34]

Is it possible to get reservoir outflows and volumes directly? Thanks.

[anonymous34]

Also, is it possible to have a reservoir with volume but no outflow?

[rchlumsk]

In response to the last couple of questions:

Q: Is it possible to get reservoir outflows and volumes directly?

No, currently you would need to look at the stages outputted and use the reservoir’s stage-discharge curves to estimate the Q and V. However this could be easily implemented in raven to output the flow and volume.

Q: Is it possible to get reservoir outflows and volumes directly?

Yes, all depends on the storage-rating curve that is supplied. Be careful in supplying the curves and ensure that they are physically representative. In some reservoir operations, for example during high flow, the reservoir operation may be to hold water and thus have increasing volumes without outflow.

[anonymous34]

The Raven manual mentions a 'ReservoirStages.csv' file, how does this get outputted?

[rchlumsk]

The Raven manual mentions a 'ReservoirStages.csv' file, how does this get outputted?

If there are reservoirs in Raven and there is at least one gauged one, the file will be automatically created.

[anonymous77]

Am I able to clump impermeable area with lake areas to generate direct runoff? Or should I separate my lakes out of the model and come up with an inflow using direct rain over the lake area. Can this be treated in Raven?

[rchlumsk]

Am I able to clump impermeable area with lake areas to generate direct runoff? Or should I separate my lakes out of the model and come up with an inflow using direct rain over the lake area. Can this be treated in Raven?

If you use a LAKE profile beneath the HRU (with zero layers), it will automatically generate direct runoff to the surface water network. This would be written in the .rvp file as (e.g.)

Code: Select all

:SoilProfiles
     LAKE, 0
     GLACIER, 0
     SOIL_A, 3, SAND, 0.9, SILT, 2.0, CLAY, 3.0
:EndSoilProfiles

Raven automatically does this with all soil profiles with the prefix LAKE.

[Carlosi]

Am I able to clump impermeable area with lake areas to generate direct runoff? Or should I separate my lakes out of the model and come up with an inflow using direct rain over the lake area. Can this be treated in Raven?

Thanks Robert, I didn't know it automatically did that with the prefix.