Sullivan Branch begins in northern Davidson Township. It flows east for a short distance before turning southeast and entering a valley. After more than a mile, it receives the tributary Ore Run and turns south-southeast. The valley of the stream is approximately deep at this point. Eventually, Sullivan Branch receives the tributary Hunts Run and turns southeast. Shortly afterwards, it merges with Big Run to form East BranchFishing Creek.
Tributaries
Tributaries of Sullivan Branch include Ore Run, Hunts Run, and Pigeon Run. The watershed of Ore Run has an area of. The watershed of Hunts Run has an area of. The watershed of Pigeon Run has an area of.
The discharge of Sullivan Branch at its headwaters is 3,276,000 gallons per day. The concentration of aluminum in Sullivan Branch at its headwaters is 0.43 milligrams per liter. The daily load of aluminum there is. The averaged acidity and alkalinity at an upstream point, both expressed in units of mg CaCO3 per litre, were found to be 7.23 and 5.03 respectively. The daily loads of these substances are and, respectively. Downstream of the tributary Ore Run, the discharge of Sullivan Branch is 11,177,000 gallons per day. The aluminum concentration at this point is 0.39 milligrams per liter and the load is per day. The acidity concentration is 6.70 milligrams per liter and the daily alkalinity load is. The alkalinity concentration is 5.33 milligrams per liter and the daily alkalinity load is. Downstream of the tributary Pigeon Run, the discharge of Sullivan Branch is 14,693,000 gallons per day. The concentrations of aluminum, acidity, and alkalinity are 0.37, 7.57, and 5.57 milligrams per liter, respectively. The daily load of aluminum is. The load of acidity is per day and the alkalinity load is per day.
The pH of Sullivan Branch at its headwaters is 3.99. Below Ore Run, the pH is 4.11 and below Pigeon Run, it is 4.19. The average temperature is at the stream's headwaters, downstream of Ore Run, and below Pigeon Run. At the headwaters of Sullivan Branch, the concentrations of dissolved oxygen and dissolved organic carbon are 10.40 and 3.322 milligrams per liter, respectively. Below Ore Run, the dissolved oxygen concentration is 9.87 milligrams per liter and the concentration of dissolved organic carbon is 3.232 milligrams per liter. Downstream of Pigeon Run, the concentrations of these substance are 10.09 and 3.190 milligrams per liter, respectively. Sullivan Branch experiences chronic acidification throughout. As of 2011 it was not clear how much the acidity was due to sulfuric acid coming from the atmosphere and how much due to organic acids derived from humic substances. A total of of streams in the watershed of Sullivan Branch are considered to be impaired. This includes parts of all three of its tributaries and its unnamed tributaries. The water quality of the stream is considered to be poor in normal conditions and very poor in high flow conditions. Its water quality is significantly degraded by its tributaries.
Geography and geology
The headwaters of Sullivan Branch are on North Mountain. A plateau separates the stream from another stream known as Heberly Run. The elevation of the stream at its mouth is between and above sea level. The elevation of the stream's source is between and above sea level. The gradient of Sullivan Branch is about equal to that of Kitchen Creek.
Watershed
The watershed of Sullivan Branch has an area of. There are at least ten waterfalls on Sullivan Branch, some of which are unnamed. The shapes of these waterfalls include bridal veil falls and wedding cake falls. The highest waterfall is the Fifth Falls, which have a height of. The lowest waterfall is the Tenth Falls, which have a height of. Several of the stream's tributaries also have waterfalls on them. Proposed methods to increase alkalinity in the Sullivan Branch watershed include high flow buffer channels, forest surface liming, in-stream limestone sand dosing, and road liming. The restoration of the stream is estimated to cost $600,000. Sullivan Branch is described as "the prettiest stream in Pennsylvania" in Scott E. Brown's book Pennsylvania Waterfalls: A Guide for Hikers and Photographers.
Biology
As a tributary of East Branch Fishing Creek, Sullivan Branch is designated as a high-quality coldwater fishery. Plants found along Sullivan Branch include red trillium, violets of various colors, and squirrel corn. Hobblebush also occurs on the stream's edges.
