# Release

If a hydro power plant has unregulated inflow, inflow going directly into the power plant outside of the reservoir, the discharge and bypass variable is combined with the unregulated inflow into a new variable, release. This introduces a new constraint for unregulated inflow, UNREG.

$$ \\{i \in plants\ with\ unregulated\ inflow,\ k \in \\{0, 1, ..., timesteps - 1\\}\\}$$

$$ UNREG(i,k): dis(i,k) + byp(i,k) - rel(i,k) = UnregulatedInflow(i,k)\ :\ Mm^3 $$

The release variable is substituted into the reservoir balance. Reservoir balance without unregulated inflow:

$$ RESBAL(i,k): res(i,k) - res(i,k-1) = Inflow(i,k) - (dis(i,k) + byp(i,k))$$

Reservoir balance with unregulated inflow:

$$ RESBAL(i,k): res(i,k) - res(i,k-1) = Inflow(i,k) - rel(i,k))$$

In the case that the bypass path has a minimum bypass constraint, the minimum bypass layer is also substituted into the UNREG constraint:

$$ UNREG(i,k): dis(i,k) + byp(i,k) + byp_{min}(i,k) - rel(i,k) = UnregulatedInflow(i,k)\ :\ Mm^3 $$