A reservoir can be placed upstream of the treatment area to modulate and/or treat inflows from the basin.

This algorithm is an alternative to modeling the reservoir as a separate DMSTA case & feeding output to STA directly.

A reservoir may be beneficial if STA treatment efficiency is found to deteriorate at high flow rates or if bypass frequency is high.

Output from the reservoir simulation is contained on the "Reservoir" & "GraphsReservoir" sheets.

The reservoir parameters is specified by the following:

F_PEAK

ratio of maximum to mean inflow to downstream treatment area (regulation objective)

V_RMAX

maximum storage reservoir volume (hm3)

T_RES

hydraulic residence time of reservoir (days)

K2_RES

second-order phosphorus decay rate in reservoir (1/yr / ppb)

If T_RES > 0

All basin flow is routed through reservoir

Reservoir outflow to STA is proportional to reservoir storage volume ( Qout = V / T_RES), subject to constraints:

Q_OUT <= Q_PEAK

treatment capacity

constraint ignored if input Q_PEAK = F_PEAK x Q_BASIN

Vres = V_RMAX

reservoir is full

constraint ignored if input V_RMAX = 0

If T_RES = 0

Reservoir is used for peak flow control only (low & average flows go directly to STA)

Reservoir accepts basin flows exceeding Q_PEAK until it is full.

Outflow equals specified maximum inflow to STA (Q_{PEAK =}F_PEAK x Q_BASIN) - basin flow

i.e., the reservoir empties as quickly as possible after the event without violating the peak inflow constraint.

If the reservoir is full:

The STA peak inflow constraint is ignored.

All basin flow is routed directly to STA (where it may be bypassed)

Continues until storage is available in reservoir

If input parameters F_PEAK = 0 & T_RES = 0, no reservoir is simulated.

Since the reservoir water-balance model does not consider rainfall & et, the peak storage volumes are probably under-estimated.

Note that the specified 'Maximum Inflow' to the treatment area (Row 29 of parameters input sheet) triggers bypass around the

treatment area, but does not influence the reservoir simulation. See "DMSTA Hydraulics, Bypass, & Seepage Computations"

The phosphorus mass-balance is tracked, so that outflow load = inflow load on the average unless specified K2_RES> 0.

Phosphorus retention is modeled as a second order reaction (proportional to volume & square of p concentration)

The phosphorus retention model has not been tested regionally (data needed).

Typical rate coef K2_RES ~ 0.1 - 0.2

1/yr/ppb

Effect of extended dryout periods on model performance unknown.

The phosphorus retention model was originally developed using data from Corps of Engineer reservoirs.

It is appropriate for systems in which phosphorus removal is controlled by sedimentation & phytoplankton.

The reservoir P uptake model has not been tested against data from Florida reservoirs.

References:

06/08/02