Lin S.D. Water and Wastewater Calculations Manual

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state fish contaminant monitoring program. The degree of fish con-

sumption use support attainment can be found in Table 2.11.

Overall use. After assessing individual lake uses, the overall use sup-

port of a lake can be determined. The overall use support methodology

aggregates the use support attained for each of the individual lake uses

assessed (i.e. aquatic life, recreation, swimming, drinking water supply,

and fish consumption). The aggregation is achieved by averaging indi-

vidual use attainments for a lake. For instance, individual uses meet-

ing full, full/threatened, partial/minor, partial/moderate, or nonsupport

are assigned values from five (5) to one (1), respectively. The values

assigned to each individual use are subsequently summed and averaged.

The average value is rounded down to the next whole number, which is

then applied to assign an overall lake use attainment. Full support

attainment is assigned to an average value of 5; full/threatened, 4; partial/

minor, 3; partial/moderate, 2; and nonsupport, 1.

Example: The mean TSI is determined by averaging 18 months’ SD-TSI, TP-

TSI, and CHL-TSI values at station 1-surface (deepest station) and station

2-surface (midlake station) of a central Illinois lake, for values of 54.3 and 58.9,

respectively. All Secchi disc readings were greater than 24 in. The mean of

nonvolatile suspended solids concentrations observed during 1996–97 at sta-

tions 1-surface and 2-surface are 5 and 7 mg/L, respectively. Estimated macro-

phyte impairment and other observed data are given in Table 2.12. Determine

support of designated uses in the lake based on Illinois lake-use support

assessment criteria.

solution: Solve for station 1 (Steps 1 to 5); then station 2 (Step 6) can be

solved in the same manner

Lakes and Reservoirs 165

TABLE 2.11 Assessment Criteria for Fish Consumption Use in Illinois Lakes

Degree of use support Criteria

Full No fish advisories or bans are in effect.

Partial/moderate Restricted consumption fish advisory or ban in effect for

general population or a subpopulation that could be at

potentially greater risk (pregnant women, children).

Restricted consumption is defined as limits on the number or

meals or size of meals consumed per unit time for one or

more fish species. In Illinois, this is equivalent to a Group II

advisory.

Nonsupport No consumption fish advisory or ban in effect for general

population for one or more fish species; commercial fishing

ban in effect. In Illinois, this is equivalent to a Group III

advisory.

SOURCE: Illinois EPA (1996)

Step 1. Assess aquatic life use

1. Find ALI points for TSI

Since mean TSI ⫽ 54.3, TSI points ⫽ 40 is obtained from Table 2.5,

section 1.

2. Determine macrophyte impairment (MI) point of ALI points

The estimated macrophyte impairment is 5% of the lake surface area.

From section 2 of Table 2.5, the MI point is 10.

3. Determine mean nonvolatile suspended solids (NVSS) of ALI point

The NVSS ⫽ 5 mg/L. From section 3 of Table 2.5, we read NVSS point ⫽ 0.

4. Calculate total ALI points

Total ALI points ⫽ TSI points ⫹ MI points ⫹ NVSS points

⫽ 40 ⫹ 10 ⫹ 0

⫽ 50

166 Chapter 2

Table 2.12 Use Support Assessment for Otter Lake, 1996–97

Station 1 Station 2

value ALI points* value ALI points

I. Aquatic life use

1. Mean trophic state index 54.3 40 58.9 40

2. Macrophyte impairment ⬍ 5% 10 ⬍ 5% 10

3. Mean NVSS 5 mg/L 0 7 mg/L 5

Total points: 50 55

Criteria points: ⬍ 75 ⬍ 75

Use support: Full Full

Value RUI points* Value RUI points

II. Recreation use

1. Mean trophic state index 54.3 54 58.9 59

2. Macrophyte impairment ⬍ 5% 0 ⬍ 5% 0

3. Mean NVSS 5 mg/L 5 7 mg/L 5

Total points: 59 64

Criteria points: ⬍ 60 65 ⱕ R ⱕ 75

Use support: Full Partial

Degree of Degree of

Value use support Value use support

III. Swimming use

1. Secchi depth ⬍ 24 in 0% Full 0% Full

2. Fecal coliform ⬎ 200/100 mL 0% Full 0% Full

3. Mean trophic state index 54.3 Full 58.9 Full

Use support: Full Full

IV. Drinking water supply Full Full

V. Overall use 54

Use support: Full Full/threatened

*ALI, aquatic life use impairment index; RUI, recreation use impairment index.

5. Determine the degree of aquatic life index use support

Since ALI points ⫽ 50 (i.e. ⬍ 75) of the critical value, and there are poten-

tial threats to aquatic life impairment, the degree of use support is full from

Table 2.6.

Step 2. Assess recreation use

1. Determine the mean TSI of RUI point

Since mean TSI value is ⫽ 54.3, then RUI points for TSI ⫽ 54, from

section 1 of Table 2.7.

2. Determine macrophyte impairment of RUI point

Since ⬍ 5% of the lake’s surface area is covered by weeds, from section 2

of Table 2.7, the RUI point for MI ⫽ 0.

3. Determine sediment impairment

The mean NVSS is 5 mg/L. From section 3 of Table 2.7, for sediment

impairment (NVSS), RUI ⫽ 5.

4. Compute total RUI points

Total RUI points ⫽ TSI value ⫹ MI points ⫹ NVSS points

⫽ 54 ⫹ 0 ⫹ 5

⫽ 59

5. Determine the degree of recreation use support

Total RUI points ⬍ 60, therefore the degree of recreation use is considered

as Full from Table 2.8.

Step 3. Assess swimming use

1. Based on Secchi disc transparency

Since no Secchi depth is less than 24 in, from Table 2.9, the degree of use

support is classified as Full.

2. Fecal coliform criteria

No fecal coliform density is determined

3. Based on trophic state index

Mean TSI ⫽ 54.3. From Table 2.9, it can be classified as Full.

4. Determine swimming use support

Based on the above use analysis, it is assessed as Full for swimming use

support.

Step 4. Assess drinking water supply use

There was no drinking water supply closure or advisories during the

1996–97 study period. Also no chemicals were applied to the lake. It is con-

sidered as Full use support for drinking water supply.

Lakes and Reservoirs 167

Step 5. Assess overall use for station 1

On the basis of overall use criteria, the assigned score values for each indi-

vidual use are as follows:

Aquatic life use 5

Recreation use 5

Swimming use 5

Drinking water use 5

Total 20

The average value is 5. Then the overall use for station 1 is attained as Full

(Table 2.12).

Step 6. Assess for station 2

Most assessments are as for station 1 except the following:

1. Recreation use:

From Table 2.12, we obtain RUI points ⫽ 64 which is in the critical range

60 ⱕ; RUI ⬍ 75; therefore, the degree of research on use is considered as

partial/minor from Table 2.8.

2. The assigned scores for overall use are

Aquatic life use 5

Recreation use 3

Swimming use 5

Drinking water supply 5

Total 18

The average is 4.5, which is rounded down to the next whole number, 4. Then,

the overall use for station 2 is attained as full/threatened.

5.11 Lake budgets (ﬂuxes)

Calculation of lake budgets (fluxes) usually includes the hydrologic

budget, nutrients (nitrogen and phosphorus) budgets, and the sediment

budget. These data should be generated in Phases I, II, and III studies.

Hydrologic budget. A lake’s hydrologic budget is normally quantified on

the basis of the height of water spread over the entire lake surface area

entering or leaving the lake in a year period. The hydrologic budget of

a lake is determined by the general formula:

Storage change ⫽ inflows ⫺ outflows (2.18)

⌬S ⫽ P ⫹ I ⫹ U ⫺ E ⫺ O ⫺ R (2.18a)

(Equations. (2.18) and (2.18a) are essentially the same.)

168 Chapter 2

In general, inflow to the lake includes direct precipitation (P ), watershed

surface runoff (I ), subsurface groundwater inflow through lake bottom

(U ), and pumped input, if any. Outflows include lake surface evaporation

(E), discharge through surface outlet (O), outflow through lake bottom

(groundwater recharge, R), and pumped outflow for water supply use, if any.

The storage term is positive if the water level increases in the period

and negative if it decreases. The unit of the storage can be, simply, in

(or mm) or acre ⭈ ft (or ha ⭈ cm). The hydrologic budget is used to com-

pute nutrient budgets and the sediment budget and in selecting and

designing pollution control and lake restoration alternatives.

Example: Table 2.13 illustrates the hydrologic analysis from Vienna

Correctional Center Lake, a water supply lake (Bogner et al., 1997). Date

needed for evaluating various parameters (Eq. (2.8)) to develop a hydrologic

budget for the lake were collected for a 1-year period (October 1995 to

September 1996). Table 2.13 presents monthly and annual results of this

monitoring. Data sources and methods are explained as below:

solution:

Step 1. Determine lake storage change

Lake storage change was determined on the basis of direct measurement

of the lake level during the study period. Lake-level data were collected by

Lakes and Reservoirs 169

TABLE 2.13 Summary of Hydrologic Analysis for Vienna Correction Center Lake,

October 1995–September 1996

Ground- Water

Direct water Monthly supply

Storage preci- inflow Surface evapo- Spillway with-

change pitation outflow (⫺) inflow ration discharge drawal

Date (acre⭈ ft) (acre⭈ ft) (acre⭈ ft) (acre ⭈ ft) (acre ⭈ ft) (acre⭈ ft) (acre⭈ ft)

1995

October ⫺56 9 7 3 14 0 61

November ⫺14 16 ⫺13 40 7 0 49

December ⫺13 14 ⫺231 4 052

1996

January 40 19 18 63 4 0 55

February ⫺1142419 6 051

March 153 27 36 154 12 0 52

April 74 34 31 221 20 142 50

May ⫺8 33 24 262 28 244 55

June ⫺37 21 ⫺376 30 4259

July ⫺55 30 ⫺611 33 058

August ⫺76 3 4 4 29 0 59

September ⫺36 34 ⫺18 27 21 0 58

Annual ⫺39 244 102 911 208 428 658

automatic water-level recorder at 15-min intervals and recorded at 6-h inter-

vals or less. On the basis of water-level record frequency, changes in storage

were estimated by multiplying the periodic change in lake storage from the

water-level recorder by the lake surface area (A) to determine net inflow or

outflow volume.

Step 2. Compute direct precipitation

Direct precipitation was obtained from the precipitation record at the

University of Illinois’ Dixon Spring Experiment Station. The volume of direct

precipitation input to the lake was determined by multiplying the precipita-

tion depth by A.

Step 3. Compute spillway discharge Q

The general spillway rating equation was used as below:

Q ⫽ 3.1 LH

1.5

⫽ 3.1(120)(H

1.5

)

Where L ⫽ spillway length, ft

H ⫽ the height or water level exceeding the spillway

Step 4. Estimate evaporation

Evaporation was estimated using average monthly values for Carbondale in

Lake Evaporation in Illinois (Robert and Stall, 1967). Monthly evaporation

rates were reduced to daily rates by computing an average daily value for each

month. The daily lake surface evaporation volume was determined for the

study period by multiplying the daily average evaporation depth by A.

Step 5. Obtain water supply withdraw rate

The daily water supply withdraw rates were taken directly from the monthly

reports of the water treatment plant.

Step 6. Estimate groundwater inflow and surface inflow

Groundwater inflow and surface water inflow could not be estimated from

direct measurements and instead were determined on the basis of a series of

sorting steps:

a. If the daily spillway discharge was zero and no rainfall occurred during

the preceding 3 days, all inflow was attributed to seepage from the ground-

water system.

b. If there was precipitation during the preceding 3-day period, or if there

was discharge over the spillway, the groundwater input was not deter-

mined in Step 6a. In this case, a moving average was used for the ground-

water parameter based on the Step 6a values determined for the

preceding 5-day and following 10-day periods.

c. If the daily balance indicated an outflow from the lake, it was attributed

to seepage into the groundwater inflow/outflow to the lake; the surface

water inflow to the lake was determined to be any remaining inflow

volume needed to achieve a daily balance.

170 Chapter 2

Step 7. Summary

Table 2.14 summarizes the hydrologic budget for the 1-year monitoring period.

The inflows and outflows listed in Table 2.14 are accurate within the limits

of the analysis. During the study period, 18.9, 70.4, 7.8, and 2.9% of the inflow

volume to the lake were, respectively, direct precipitation on the lake surface,

watershed surface runoff, groundwater inflow, and decrease in storage.

Outflow volume was 50.9% water supply withdrawal, 33.0% spillway over-

flow, and 16.1% evaporation.

Nutrient and sediment budgets.

Although nitrogen and phosphorus are

not the only nutrients required for algal growth, they are generally con-

sidered to be the two main nutrients involved in lake eutrophication.

Despite the controversy over the role of carbon as a limiting nutrient,

the vast majority of researchers regard phosphorus as the most fre-

quently limiting nutrient in lakes.

Several factors have complicated attempts to quantify the relationship

between lake trophic status and measured concentrations of nutrients

in lake waters. For example, measured inorganic nutrient concentra-

tions do not denote nutrient availability but merely represent what is

left over by the lake production process. A certain fraction of the nutri-

ents (particularly phosphorus) becomes refractory while passing through

successive biological cycles. In addition, numerous morphometric and

chemical factors affect the availability of nutrients in lakes. Factors

such as mean depth, basin shape, and detention time affect the amount

of nutrients a lake can absorb without creating nuisance conditions.

Nutrient budget calculations represent the first step in quantifying the

Lakes and Reservoirs 171

TABLE 2.14 Annual Summary of the Hydrologic Budget for Vienna Correction Center

Lake, October 1995–Septmber 1996

Inflow volume Outflow volume Inflow Outflow

Source (acre ⭈ ft) (acre ⭈ ft) (%) (%)

Storage change 37.1 2.9

Direct 243.8 18.9

precipitation

Surface inflow 910.2 70.4

Groundwater 100.6 7.8

inflow

Spillway 426.9 33.0

discharge

Evaporation 207.8 16.1

Water supply 656.9 50.9

withdrawal

Totals 1291.7 1291.7 100.0 100.0

Note: Blank spaces—not applicable; 1 acre ⭈ ft ⫽ 1233 m

dependence of lake water quality on the nutrient supply. It is often

essential to quantify nutrients from various sources for effective man-

agement and eutrophication control.

A potential source of nitrogen and phosphorus for lakes is watershed

drainage, which can include agricultural runoff, urban runoff, swamp

and forest runoff, domestic and industrial waste discharges, septic tank

discharges from lakeshore developments, precipitation on the lake sur-

face, dry fallout (i.e. leaves, dust, seeds, and pollen), groundwater

influxes, nitrogen fixation, sediment recycling, and aquatic bird and

animal wastes. Potential sink can include outlet losses, fish catches,

aquatic plant removal, denitrification, groundwater recharge, and sed-

iment losses.

The sources of nutrients considered for a lake are tributary inputs

from both gaged and ungaged streams, direct precipitation on the lake

surface, and internal nutrient recycling from bottom sediments under

anaerobic conditions. The discharge of nutrients from the lake through

spillway is the only readily quantifiable sink.

The flow weighted-average method of computing nutrient transport

by the tributary are generally used in estimating the suspended sedi-

ments, phosphorus, and nitrogen loads delivered by a tributary during

normal flow conditions. Each individual measurement of nitrogen and

phosphorus concentrations in a tributary sample is used with the mean

flow values for the period represented by that sample to compute the

nutrient transport for the given period. The total amount of any specific

nutrient transported by the tributary is given by the expression

(Kothandaraman and Evans, 1983; Lin and Raman, 1997):

(2.19a)

(2.19b)

where T ⫽ total amount of nutrient (nitrogen or phosphorus) or TSS,

lb or kg

⫽ average daily flow in cfs for the period represented by the

ith sample

⫽ concentration of nutrient, mg/L

⫽ number of days in the period represented by the ith

sample

A similar algorithm with appropriate constant (0.0255) can be used for

determining the sediment and nutrient transport during storm events.

For each storm event, n

is the interval of time represented by the ith

sample and q

is the instantaneous flow in cfs for the period represented

T kg 5 2.446

⌺

T lb 5 5.394

⌺

172 Chapter 2

by the ith sample. The summation is carried out for all the samples col-

lected in a tributary during each storm event. An automatic sampler can

be used to take stormwater samples.

The level of nutrient or sediment input is expressed either as a con-

centration (mg/L) of pollutant or as mass loading per unit of land area

per unit time (kg/ha ⭈ yr). There is no single correct way to express the

quantity of nutrient input to a lake. To analyze nutrient inputs to a lake,

the appropriate averaging time is usually 1 year, since the approximate

hydraulic residence time in a lake is of this order of magnitude and the

concentration value is a long-term average.

5.12 Soil loss rate

Specific soil loss rate from the watershed (for agricultural land, large

construction sites, and other land uses of open land) due to rainfall can

be estimated through the universal soil loss equation or USLE

(Wischmeier and Smith, 1965):

A ⫽ R ⫻ LS ⫻ K ⫻ C ⫻ P (2.20)

where A ⫽ average soil loss rate, tons/(acre ⭈ yr)

R ⫽ rainfall factor

L ⫽ slope length, ft

S ⫽ slope steepness, %

LS ⫽ length-slope factor or topographic factor (not L times S)

K ⫽ soil erodibility

C ⫽ cropping and management factor

P ⫽ conservation practice factor

The slope steepness, slope length, cropping factors, and erodibility of

each soil type cropping factor can be determined for various land uses

in consultation with the local (county) USDA Soil and Water Conservation

Service.

The R ⫻ P factor value is assigned as 135 for Illinois agricultural crop-

land and 180 for other land uses. Wischmeier and Smith (1965) and

Wischmeier et al. (1971) are useful references. The value of P is one for

some CRP (Conservation Reserve Program) implementations after 1985.

Based on the soil information compiled in the watershed or sub-

watersheds (for example, Table 2.15), the soil loss rates can be computed.

The soil loss for each soil type for each subwatershed is obtained by mul-

tiplying the rate and soil acreage. The total soil loss for the watershed

is the sum of soil loss in all subwatersheds expressed as tons per year.

Excluding the lake surface area, the mean soil erosion rate for the water-

shed is estimated in terms of tons/(acre ⭈ yr).

Lakes and Reservoirs 173

The USLE accounts for a series of factors that are the most signifi-

cant influences on the erosion of soil by precipitation. The USLE is a cal-

culation of in-field soil losses and does not account for deposition from

the field to the stream or lake. Redeposition within the field or drainage

system is accounted for by a sediment delivery ratio that defines the pro-

portion of the upstream soil losses that actually pass through the stream

then to the lake.

The RUSLE (Revised Universal Soil Loss Equation) is an updated ver-

sion of the USLE and was adopted recently by the USDA and many

states. The original USLE has been retained in RUSLE; however it has

been put into a computer program to facilitate calculations, the tech-

nology for factor evaluation has been altered, and new data has been

introduced to evaluate each factor under more specific conditions. There

are three tables for LS value determinations.

For the following example, taking the sum of annual loss for each soil

type, the total annual soil loss in the Nashville City Reservoir water-

shed (984.3 acres) is 2.953 tons (Table 2.16). This analysis shows that

the average annual soil loss in the watershed is 3.5 tons/(acre ⭈ yr).

Example: Estimate the watershed soil loss rate for the Nashville City

Reservoir watershed in Washington County, Illinois (southern). Use USLE

instead of RUSLE, since new factors are not yet available.

174 Chapter 2

TABLE 2.15 Soil Classiﬁcations in the Nashville City Reservoir Watershed

Soil type Soil name Slope Area (acres)

2 Cisne silt loam – 38.0

3A Hoyleton silt loam 0–2 14.9

3B Hoyleton silt loam 2–5 11.9

5C2 Blair silt loam, eroded 5–10 36.1

5C3 Blair silt loam, severely eroded 5–10 31.0

5D3 Blair silt loam, severely eroded 10–15 9.8

8D2 Hickory silt loam 10–15 6.2

12 Wynoose silt loam – 186.0

13A Bluford silt loam 0–2 208.4

13B Bluford silt loam 2–5 73.7

13B2 Bluford silt loam, eroded 2–5 17.5

14B Ava silt loam 2–5 14.2

48 Ebbert silt loam – 7.5

912A Dartstadt-Hoyleton complex 0–2 61.4

912B2 Dartstadt-Hoyleton complex, eroded 2–5 164.7

991 Huey-Cisne complex – 32.6

1334 Birds silt loam – 10.9

3415 Orian silt loam, wet – 17.5

Water 42.0

Total 984.3

Note: – means flat, using 0.5% for calculation

SOURCES: USDA, 1998; J. Quinn, personal communication, 2000