Controlling Internal Phosphorus Loading

in Barr Lake and Milton Reservoir

Ken Wagner

Middle

Fo

rk

South Fork

Tarryall Creek

South Platt e North Fork

Bear Creek

Clear Creek

Big

Dry

Cre

ek

Ch

err

y C

ree

k

South

Pla

tte R

iver

Denver

Ü0 10 20 305

Miles

J:\Water\ProjectFiles\P120\12309_BMW\GIS\Whole_Watershed\Whole_Watershed.mxd

Map of Barr-Milton Watershedin North-Central Colorado

Datashed

Whole_Watershed

The full Barr-

Milton watershed

Pretty clearly,

watershed

processes are

important to

water quality in

the two

reservoirs.

Beebe C

an

al

Third CreekSecond Creek

First Creek

Pla

tte V

alle

y Canal

Fulton D

itch

Sou

th P

latte R

iver

Sand Creek

Cherry CreekBear Creek

BarrLake

MiltonReservoir

Ü0 10 205

Miles

J:\Water\ProjectFiles\P120\12309_BMW\GIS\Whole_Watershed\Datashed.mxd

Map of Barr-Milton Datashedin North-Central Colorado

Reaches

Datashed

The immediate Barr-

Milton watershed

Here we get a sense

for the off-line

nature of these

reservoirs; the

watershed remains

important, but the

routing and timing

of inflows has a

major impact

Sediment sampling stations in Barr-Milton

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4.00

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Oxy

gen

De

man

d (

g/m

2/d

ay)

Date

Oxygen demand in Barr Lake

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0.50

1.00

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4.00

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Oxy

gen

De

man

d (

g/m

2/d

ay)

Date

Oxygen demand in Milton Reservoir

Oxygen demand in Barr-Milton

Sediment organic content in Barr-Milton

Fe-P concentration in Barr-Milton

Potential Internal Loading

Based on the Fe-P concentrations in areas

potentially exposed to anoxia and probable

release of organic P through decomposition,

the internal P load to Barr or Milton is <5% of

current external loading and would be <25%

of the load if the TMDL was met through

external load control.

Potential Internal Load Controls

• Dredging – Sets waterbody back in time,

improves multiple aspects of reservoirs, but

very expensive ($20 M for Barr, $36 M for

Milton)

• Phosphorus Inactivation – Can bind P in

sediment (done once per decade or 2) or in

water column (annual maintenance treatment)

• Oxygenation – Relieves demand, limits Fe-P

availability, but may release more organic P

• Artificial Circulation – Mixes water column,

oxygenates, homogenizes, tends to shift algae

• Hybrid Circulation and Inactivation System

Hybrid Circulation and Inactivation System

Circulation:

• Provides oxygenation and CO2 equilibration – will

lower pH even without any algal effect

• Will lower internal load, but may make nutrients more

available

• Will not reduce algae biomass in shallow system, but

may shift algae away from buoyant cyanobacteria

Inactivation:

• Counters P availability, reduces overall fertility

• Coagulant properties settle many solids as well

Combination can manage in-reservoir water quality in

support or in place of more expensive watershed

controls

Recommendation

If watershed management continues and a

phosphorus inactivation system is built on

the canal leading to Barr Lake, no action may

be needed.

If more immediate improvement is desired,

installation of a combination circulation and P

inactivation system in each waterbody would

be the least expensive way to meet water

quality goals and can substitute for more

expensive watershed management needs.

Questions?

I think I’m

gonna need

another

one…