Knowing how much water Avoyelles Parish, in central Louisiana, has, how it is used and how good it is helps water managers and residents look after it. This U.S. Geological Survey fact sheet, prepared with the Louisiana Department of Transportation and Development, sums it up.
How the water is used
In 2014 the parish withdrew about 70 million gallons a day (Mgal/d): 59.27 from groundwater and 10.95 from surface water.
| Use (2014) | Groundwater | Surface water | Total (Mgal/d) |
|---|---|---|---|
| Aquaculture | 18.43 | 6.14 | 24.58 |
| Rice irrigation | 21.35 | 1.12 | 22.47 |
| General irrigation | 14.72 | 3.68 | 18.39 |
| Livestock | 0.15 | 0.00 | 0.15 |
| Public supply | 4.45 | 0.00 | 4.45 |
| Rural domestic | 0.18 | 0.00 | 0.18 |
Agriculture — aquaculture, irrigation and livestock — took 93 percent (65.59 Mgal/d). Figures are rounded, so they may not add up exactly.
Water withdrawals, 1960–2014, measured every five years to 2010 and again in 2014; they peaked in 2014. Groundwater withdrawals rose from 3.99 Mgal/d in 1960 to 59.27 in 2014.
| Source (2014) | Mgal/d |
|---|---|
| Alluvial aquifers | 47.45 |
| Terrace aquifers | 7.50 |
| Evangeline aquifer | 4.32 |
| Jasper aquifer system | 0.01 |
| Surface water | 10.95 |
The aquifers
Avoyelles Parish. Shading shows the altitude of the base of fresh groundwater; A–A′ is the section below. From the USGS fact sheet.
The main freshwater aquifers are the alluvial and terrace aquifers and the Evangeline aquifer. The Jasper aquifer system (the Carnahan Bayou and Williamson Creek aquifers) and the Jasper equivalent aquifer system may also hold fresh water, but little is drawn from them.
Where fresh groundwater — 250 milligrams per litre (mg/L) of chloride or less — ends varies across the parish:
| Area | Base of fresh groundwater |
|---|---|
| Centre | in the alluvial aquifers, from less than 100 to more than 150 feet below NGVD 29 |
| East | in the Jasper equivalent system, from less than 200 to more than 1,000 feet below |
| Northwest corner | in the Jasper system, from less than 150 to more than 400 feet below |
| Southwest | in the Evangeline aquifer, from less than 300 to more than 1,000 feet below |
An idealised west-to-east section through the parish; individual sand and clay layers are not shown.
Alluvial and terrace aquifers
The alluvial aquifers — the Mississippi River alluvial and Red River alluvial — lie under the lowlands; the terrace aquifers — the Upland and Prairie terrace — under the uplands. Both are the lower parts of river and delta deposits that grade from clay and silt at the surface to sand and gravel at the base, and the sand and gravel layers are connected, so despite their names they act as one system, 50 to 150 feet thick. A silt-and-clay layer on top, from less than 5 to 50 feet thick and missing in places, confines it; its base lies from less than 100 to more than 150 feet below NGVD 29.
- Recharge: mainly rain, plus streams and rivers, and water pushed up from deeper aquifers when their pressure is high enough.
- Flow: in the 1960s groundwater moved toward the Red River in the north and northeast, the Atchafalaya in the southeast, and Evangeline Parish in the southwest — though with withdrawals up so much, that may have changed. It leaves through streams, evapotranspiration and wells.
- Water levels: at well Av-329, north of the Red River, levels varied yearly, with a lower period from about 1980 to 2002, but were stable overall from 1968 to 2012. At Av-164, south of Marksville in the Upland terrace aquifer, they varied with the seasons and fell less than 5 feet from 1966 to 2017.
| 2017 wells | Alluvial aquifers | Terrace aquifers |
|---|---|---|
| Active wells | 468 — 334 irrigation, 119 domestic, 7 industrial, 8 public supply | 115 — 44 irrigation, 50 domestic, 3 industrial, 18 public supply |
| Depths | 15–205 feet | 39–200 feet |
| Yields | 10–7,500 gallons a minute | 6–4,000 gallons a minute |
| 2014 use (Mgal/d) | 47.45 — rice irrigation 19.64, aquaculture 13.82, general irrigation 13.24, public supply 0.59, livestock 0.08, rural domestic 0.07 | 7.50 — aquaculture 4.61, rice irrigation 1.28, public supply 0.83, general irrigation 0.74, rural domestic 0.03, livestock 0.02 |
Evangeline aquifer
Fresh water occurs in the Evangeline aquifer in the southwest and southeast of the parish (where it is also called the Evangeline equivalent aquifer system), but not in the south-centre. It subcrops in southern Avoyelles and dips and thickens to the south, its top from about NGVD 29 to less than 200 feet below.
- It is made of sand layers separated by clay: more than 500 to more than 1,000 feet thick in all, with fresh-water sands totalling from less than 200 to more than 600 feet. Most sand layers are under 50 feet thick, some 100 feet or more.
- It is recharged indirectly by rain soaking through the terrace aquifers above, and is separated from the Jasper system below by the clay of the Castor Creek confining unit.
- Water levels at well Av-406, west of Hessmer, fell from about 30 feet above NGVD 29 at the first measurement in 1979 to about 16 feet above it in 2016, partly because of seasonal variation.
- Wells (2017): 135 active — 104 domestic, 24 public supply, 5 irrigation, 2 industrial; 210 to 925 feet deep; yields 1 to 690 gallons a minute.
- Use (2014): about 4.32 Mgal/d — 3.04 public supply, 0.74 general irrigation, 0.43 rice irrigation, 0.07 rural domestic, 0.04 livestock.
Water levels in wells Av-329 (Red River alluvial), Av-164 (Upland terrace) and Av-406 (Evangeline), in feet above NGVD 29.
Groundwater quality
The state's long-term monitoring sampled 137 alluvial wells (1937–2014), 74 terrace wells (1938–87) and 64 Evangeline wells (1938–2013), compared with the EPA's secondary maximum contaminant levels (SMCLs) — guidelines for taste, colour, staining and similar effects.
| Alluvial | Terrace | Evangeline | SMCL | |
|---|---|---|---|---|
| Median hardness | 410 mg/L — very hard | 220 mg/L — very hard | 17 mg/L — soft | — |
| Median iron | 11,000 µg/L | 200 µg/L | 100 µg/L | 300 µg/L |
| Samples within the iron limit | 6% | 52% | 97% | |
| Median manganese | 600 µg/L | 125 µg/L | 30 µg/L | 50 µg/L |
| Samples within the manganese limit | 2% | 40% | 64% | |
| Median dissolved solids | 568 mg/L | 416 mg/L | 584 mg/L | 500 mg/L |
Chloride and sulfate were within the SMCLs in at least 95 percent of samples from every aquifer. Iron and manganese exceeded them in more than 90 percent of alluvial samples, and median dissolved solids exceeded the limit in the alluvial and Evangeline aquifers.
Surface water
The parish lies in three subbasins: the Atchafalaya (HUC 08080101) in the southeast, the Lower Red (HUC 08040301) in the north and the Bayou Teche (HUC 08080102) in the southwest. In 2014, 10.95 Mgal/d was drawn from smaller waters — 6.14 for aquaculture, 3.68 for general irrigation and 1.12 for rice.
- Lower Red and Atchafalaya. The Red River enters from Rapides Parish and follows the parish's northeastern and eastern borders, ending at its eastern edge, where it joins Mississippi River water to form the Atchafalaya River. The Old River Control Structure, in neighbouring Concordia Parish, sends about 30 percent of the combined flow of the Mississippi and Red rivers above it into the Atchafalaya. Upstream, the Red River at Alexandria averaged 30,770 ft³/s in 1928–82; the Atchafalaya at Simmesport averaged 218,400 ft³/s in 2009–2015, with monthly averages from 354,300 in May to 105,600 in November.
- Bayou Teche. Its streams are small by comparison: Bayou Rouge, Coco Canal, Bayou des Glaises, Bayou Boeuf and the Bayou des Glaises Diversion Channel. Data are limited, but the diversion channel at Moreauville, draining 270 square miles, averaged 426.9 ft³/s in 1943–2015, with monthly averages from 797 in February to 137 in August.
Surface-water quality
Samples from the Red River near Simmesport (1977–86) and the Atchafalaya River at Simmesport (1952–77) were within the SMCLs for chloride, sulfate, iron, dissolved solids and pH in at least 90 percent of cases.
| Red River | Atchafalaya River | |
|---|---|---|
| Median hardness | 74 mg/L — moderately hard | 110 mg/L — moderately hard |
| Median dissolved oxygen | 7.5 mg/L | 8 mg/L |
| Median pH | 7.1 | 7.6 |
| Median dissolved solids | 187 mg/L | 197 mg/L |
Five mg/L of dissolved oxygen is generally considered the minimum for a diverse community of freshwater warm-water life, including sport fish.
Sources
- White, V.E., 2020, Water resources of Avoyelles Parish, Louisiana: U.S. Geological Survey Fact Sheet 2020–3011, prepared in cooperation with the Louisiana Department of Transportation and Development. https://pubs.usgs.gov/publication/fs20203011
- The tables, figures and captions come from the fact sheet's PDF, which the web version lacks.
- Rewritten in hubnx's own words.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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