For many observers, the most beautiful of Great Swamp’s tributaries is the Primrose Brook, which has its headwaters in the Jockey Hollow section of the Morristown National Historical Park. Arising from this undisturbed birthplace, Primrose Brook flows through the least developed sub-watershed in Great Swamp. This combination of factors makes the brook relatively pristine, second in overall stream health only to the upper reaches of the Passaic River.
The Primrose Brook sub-watershed is the second smallest sub-watershed in Great Swamp; at 3,354 acres it is just 100 acres or so larger than the Loantaka Brook sub-watershed. The brook essentially has three main tributaries with numerous small, branching tributaries feeding the main stems (see map). The western-most tributary arises along the southern side of Tempe Wick Road in Mendham Township. Flowing from an area where Jockey Hollow and Morris Area Girl Scouts lands intersect, the tributary wends its way beneath Tempe Wick Road to the north side, where it meets the second tributary. This second tributary has the most protected status of any of Great Swamp’s headwaters. The main stem and a second subsidiary stem both arise in Jockey Hollow, where development has been limited to just the paved roads and hiking paths that service the park. Fully a mile of stream runs through the park before it exits and joins the western-most tributary.
After the two tributaries merge, they form the main stem of the brook and flow beneath Tempe Wick Road and then Routes 202 and 287, which effectively bisect the brook into its northern and southern halves. Below the highways, the third major tributary to the brook enters the main stem. This tributary arises on the backside of the Harding School off Lee’s Mill Road, flows west and then south into Mount Kemble Lake, a residential community that holds 24 acres of community property around the lake. Leaving the lake at Bailey’s Mill Road, this tributary joins the main branch, which then flows through lightly developed, large lot zoned and farmland areas before crossing Lee’s Hill Road and entering the Great Swamp National Wildlife Refuge.
Despite the relative lack of development in the Primrose Brook’s sub-watershed, the Stream Monitoring program nevertheless yields data about the brook that are suggestive of potential future problems. For example, Primrose Brook currently meets all six of the 2002 Ten Town’s Committee standards for baseflow, but just three of the six standards for stormflow. Stormflow concentrations of total phosphorus varied widely in the brook, but they exceeded New Jersey standards overall. In addition, stormflow concentrations of dissolved reactive phosphorus exceeded the standards, as did, in all but two cases, concentrations of total suspended solids for trout production streams in New Jersey, a disturbing finding given that one of the brook’s great strengths is as a spawning ground for young trout. Though its baseflow conditions are considered quite good, some of its stormflow concentrations meet or exceed the high concentrations seen in Great Brook during stormflow events.
For the time being, macroinvertebrate testing in the brook shows that these fluctuating loadings have not had a significant effect on the smallest life forms in the brook. Dr. Pollock has found consistently high numbers of mayfly, stonefly, and caddisfly larvae, and he notes in his 2002 report that “Primrose Brook remains overall the highest quality stream in the watershed from the macroinvertebrate standpoint.” Nevertheless, the Ten Towns Committee notes that “fluctuations between baseflow and stormflow concentrations in this watershed should be monitored closely in future studies,” presumably to spot incipient water quality- and quantity-related problems before they emerge into full-blown environmental impacts.