Crater Lake, Oregon -589 m deep and possibly the clearest lake in the world, Transparency up to 90 m.Thermocline very deep for its size No rooted plants. Mud doesn’t accumulate on the bottom till > 90 m depth

Some of the most spectacular tectonic lakes are formed in volcanic craters.

Why is this lake so different from most lakes?

Physical features of lakes that determine habitat characteristics

•inflow from the watershed/Catchment

•Water residence time

•Morphometry, Mean depth and volume

•Thermal stratification and physical mixing

•wind./currents/wave action

•Sediment deposition

•Light extinction

Assume runoff coefficient of 0.15 m

Drainage area=7.9 km2

Lake area=0.9 km2

How much waterwould you expect flows into this lake /yr?

How much water flows into lake Beauvais lake in a year from its watershed?

Evaporation from lake surface exceeds precipitation by0.085 mm/yr

How much water flows out of the lake?

Assume runoff coefficient of 0.15 m

Drainage area=7.9 km2

Lakearea=0.9 km2

How much water would you expect flows into this lake /yr?

P─ E on lake surface= ─ 0.085 m/yr

Qi = r * DA = 0.15 m/yr * 7 x 106 m2 = 1.05 x 106m3/yr

What is the net evaporation in a year?(P-E)*A = ─ 0.085 m * lake area = ─ 0.085m/yr * 9 x 105 m2 = -7.65 x 104 m3/yr

How much water flows out of the lake in a year?

Qo = Qi + (P-E)*A = 1.05 x 106m3/yr + (─ 7.65 x 104 m3/yr) = 9.75 x 105 m3/yr

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Mean depth= 4.3 m

Lake Volume = 3.8 x 106 m3

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Mean depth= 4.3 m

Lake Volume = 3.8 x 106 m3

Water residence time=Mean renewal rate=

How much of the water flowing into this lake from its watershed could you allocate for irrigation before the lake would gradually begin to disappear?

Answer Over 92%

Lake management—the water inflow budgetor what happens when you over allocate?

The Aral Sea in the former Soviet Union—mismanaging the river water inflow

Allocation to desert irrigation > inflow minus evaporationFig. 5.19

. Effects Ecosystem collapse, loss of biodiversity, worsening of water-salt balance in the agricultural areas, pollution of rivers and drinking water, changing of the regional climate – all these are new environmental developments in Central Asia.

Calculating volume and mean depth

Mean depth = Volume/surface area

The hypsographic curve

Area under the curve = volume

Fig. 7.1 in text

•The thermocline occurs deeper in large lakes because wind energy is transmitted to greater depths

•Wind energy increases with fetch

•In small lakes convection also plays a role in determining thermocline depth

•In deep lakes only the surface layers are well mixed and quite warm, whereas the deeper parts remain cold.

Lakes partition themselves into temperature zonesThermal stratification in lakes

Fig. 11.8 in text