Geohydrology

1. Note graph comparing elevation and mean annual precipitation (ppt) at selected towns in Vermont.

2. Arithmetic average ppt is calculated to be 42.15” per year. I highlighted the values in Excel, then had the average calculated.

3. The towns of those listed that I considered to be within the Winooski River Basin are Burlington, Huntington Center, Montpelier, Mansfield and Waterbury. The annual average of ppt in those 5 towns is 46.48” per year.

4. Total volume of ppt annually falling on the Winooski River Basin:

Annual ppt = 46.48 inches/yr

(1 inch = 2.54 x 10^-5 kilometers)

Annual ppt = 46.48 inches/yr x (2.54 x 10^-5 kilometers) = 118.06 x 10^-5 km/yr

Annual ppt = 1.1806 x 10^-3 km/yr

Area of basin = 1,044 square miles

(1 square mile = 2.58 square kilometers)

Area of basin = 1,044 square miles x 2.589 = 2,703.9 square kilometers

Area of basin = 2.704 x 10³ square kilometers

Volume of ppt = annual ppt x area

= (1.1806 x 10^-3 kilometers/yr) x (2.704 x 10³ square kilometers)

Volume of ppt = 3.198 cubic kilometers/yr

5. Total run off volume per average year at Winooski River drainage area

Mean Annual discharge = 2050.66 cubic feet/sec = 2.051 x 10³ cfs.

1 cubic foot = 2.831 x 10^-11 cubic kilometers.

Mean Annual discharge = 2.051 x 10³ cfs x 2.831 x 10^-11 cubic km/cfs

Mean Annual discharge = 5.806 x 10^-8 cubic km/sec

1 year = 3.154 x 10⁷ seconds

Total discharge per year = (5.806 x 10^-8 cubic km/sec) x (3.154 x 10⁷ secs/year)

Total discharge per year = 18.31 x 10^-1 cubic kilometers/year

Mean annual volume of ppt = 3.198 cubic kilometers

Mean annual discharge = 1.831 cubic kilometers

Mean annual runoff = 3.198 cubic kilometers - 1.831 cubic kilometers

Mean annual runoff = 1.367 cubic kilometers

% volume of ppt that is runoff = 1.367/3.198 = 42.74%

6. Mean annual concentration of suspended load in tons/sq km:

%Mean (5 data points) annual suspended load = 127.4 mg/L

1 L = 1 x 10^-12 cu km

%Mean annual suspended load = 127.4 mg/1 x 10^-12 cu km = 127.4 x ¹² mg/cu km

1 metric ton = 1 Mg = 10⁹ mg

127.4 x 10 ¹² mg = 10⁹ mg 127.4 x 10 ¹² mg = # tons x 10⁹

# of tons 1 ton

# tons = 127.4 x 10 ¹² mg/10⁹ mg per ton = 127.4 x 10³ tons/cu km

%Mean annual suspended load concentration = 127.4 x 10³ tons/cu km

%Mean annual suspended load concentration x total discharge = total suspended load

discharged = 127.4 x 10³ tons/cu km x 1.832 cu km = 233.39 x 10³ ton

%Mean annual suspended load discharged = 233.39 x 10³ ton

Tons of suspended load per square kilometer = 233.39 x 10³ ton/ 2.704 x 10³ sq km

= 86.32 tons/sq km

%Tons of suspended load per square kilometer = 86.32 tons/sq km

Mean annual concentration of dissolved load in tons/sq km:

%Mean (8 data points) annual dissolved load = 82 mg/L

1 L = 1 x 10^-12 cu km

%Mean annual dissolved load = 82/10^-12 = 82 x 10¹² mg

1 metric ton = 1 Mg = 10⁹ mg

82 x 10¹² mg = 10⁹ X x 10⁹ = (82 x 10¹²⁾ x 1

X ton

%Mean annual TDS load concentration = 82 x 10³ tons/cu km

%Mean annual TDS load concentration x total discharge = total TDS load

discharged = 82 x 10³ tons/cu km x 1.832 cu km = 150.2 x 10³ tons

%Mean annual TDS load discharged = 150.2 x 10³ tons

Tons of dissolved load per square kilometer = 150.2 x 10³ tons /2.704 x 10³ sq km

= 55.54 tons/sq km

%Tons of dissolved load per square kilometer = 55.54 tons/sq km

Of the 3.198 cu km of precipitation falling in the Winooski River Basin, 1.83 cu km, or 57%, reached the river system, whereas the rest infiltrated into the ground, evaporated into the atmosphere, or was taken up by vegetation and metabolized or transpired into the atmosphere.

The flux of suspended (86.32 tons/sq km) and dissolved load (55.54 ton/ sq km) were similar. The suspended load data had an outlier in 1979, which skewed the average up. It is notable that in 1979, the concentration of suspended solids was 347 mg/L, but the TDS was only 97 mg/L. For 1979, the mean Winooski River discharge is 1,578 cfs and the 4/16/79 discharge value is 4,380 cfs. It is likely that the figures given above for suspended and dissolved load occurred during a significant spring melt, when discharge was relatively high. High discharge would mobilize more of the suspended solids., thus giving the higher value.

The Cuba data set shows a much larger concentration of TDS than does the Winooski River (Figure 2). The reason for this, as provided in the paper, is the increased weathering of the bedrock underlying the Cuban rivers. These rocks are carbonates and evaporites formed along passive margins, ophiolite sequences, and volcanic island arc rocks. Basaltic rocks are easily chemically weathered. This is different from the Winooski River basin, which is underlain by carbonates to the west and schists and phyllites to the east. The latter two lithologies are more resistant to chemical weathering.