IMPACT OF SANDSTONE STIP-MINING ON THE BRAZOS RIVER GEOMORPHOLOGY BETWEEN LAKE POSSUM KINGDOM AND LAKE GRANDBURY, PALO PINTO AND PARKER COUNTIES, TEXAS

Within the past ten years a significant increase in the Dallas-Fort Worth metroplex demand for native stone generated a flurry of sandstone stip-mining operations along the Brazos River drainage in Palo Pinto and Parker Counties. Much of the quarrying harvests the Upper Pennsylvanian (Des Moines Series, Strawn Group) fluvial, delta plain, and delta front sandstone deposits, which cap the hills of the area topography. The sandstones are very popular with the commercial and residential building industry for their variety in color and bedding. Rapidly changing depositional environments provide colors from the marine (reducing) blue-greys to the fluvial (oxidizing) buffs and roses. Also, bedding thickness extend from thinly bedded sheet sands for flagstone to thickly bedded channel sands for building stone.

Although using native stone in construction may seem environmentally positive, a catastrophic altering of the Brazos River geomorphology from unrestricted strip-mining operations has adversely shocked and changed the river ecology. Many quarry operators neglected to install adequate storm water runoff plans or none at all for control of sediment transport into the Brazos River. Without settling ponds and other runoff abatement, stripping the sandstone from hill tops expose the underlying, unconsolidated marine shales to celeritous erosion and transport to the Brazos River drainage. Literally, the river becomes clogged with a surge of extremely fine clay particles and silts. Fluctuating water levels from managed flow by the Brazos River Authority out of Possum Kingdom Lake and local flooding layer clay and silt onto river bars. Aggressive vegetation, nourished by the potting-soil mixture of mineral-rich marine clays and the river sand, quickly covers previously clean sandbars. The river swiftly transforms into a “muddy bayou” from a “sandy mountain stream.” Sediment transport capacity diminishes and becomes overwhelmed as channels shallow and braid with vegetation-stabilized bars and clogging sediment load.