Watershed-Geography

Geographical Introduction to Merrimack River Watershed

• The River and Its Watershed
• Subwatersheds
• Tributaries
• Upper, Middle, and Lower River

The River and Its Watershed
Many Native American Indian tribes once occupied the watershed and gave the river a number of different names. The most well known Indian name is merruasquamack, which means "swift water place," and is believed to have originally applied to the portion of the river between Garvin’s Falls in Bow, NH and Pawtucket Falls in Lowell, MA. Today, the river is known as the Merrimack.
The Merrimack River, which passes through central and southern New Hampshire and northeastern Massachusetts, is a vital natural resource sustaining plants, wildlife, and humans.
The Merrimack River is formed by the confluence of the Pemigewasset River, which originates from Profile Lake at the Old Man of the Mountains in Franconia Notch, NH, and the Winnipesaukee River, which has its source in a lake of the same name.
The Merrimack mainstem is formed by the marriage of the Pemigewasset and Winnipesaukee Rivers in Franklin, NH where it flows 115 miles to its meeting with the Atlantic Ocean in Newburyport, MA.
In total, the Merrimack River stretches some 180 miles. The 75% of the watershed located in New Hampshire contains most of the state's lakes and ponds.
The Merrimack River watershed was first surveyed by Goodman Woodward in 1638 and is the fourth largest watershed in New England.
A watershed is the land area from which surface runoff and groundwater flows into a particular river, lake, stream, pond, or other body of water.
It occupies 5,010 square miles and is comprised of 203 communities ranging from rural towns such as Woodstock, NH and Newbury, MA to the industrial cities of Manchester, NH, Lowell, and Lawrence, MA.
Subwatersheds
The Merrimack basin has been divided into 17 subwatersheds. A subwatershed is an area from which groundwater and surface water drains and contributes to flow in another body of water. For example, the Piscataquog River is a subwatershed because it eventually drains into the Merrimack River.  Figure 1 shows the location of each subwatershed.

 

 

•Beaver (94.66)
• Cohas (69.97)
• Contoocook (765.66)
• Merrimack (576.63)
• Nashua (530.7)
• Pemigewasset (1,001.71)
• Piscataquog (216.38)
• Pow Wow (58.63)
• Salmon Brook (31.75)
• Shawsheen (78.09)
• Soucook (91.66)
• Souhegan (219.64)
• Spicket (77.49)
• Stony Brook (45.53)
• SuAsCo (Sudbury/Assabet/Concord - 399.62)
• Suncook (257.10)
• Winnipesaukee (484.41)

 

The subwatersheds of the Merrimack River are as follows, with their approximate square mileage presented in parenthesis (information calculated by Merrimack River Watershed Council using Geographic Information Systems data compiled by the Merrimack Valley Planning Commission for planning purposes only):

Tributaries

There are several major tributaries (e.g., streams, brooks, or rivers) to the Merrimack. These tributaries may be part of a larger subwatershed and therefore may not be listed above as its own watershed. The major tributaries are:

The following table, taken from the Merrimack River Basin description written by US Fish and Wildlife Service, provides detailed information about the major tributaries of the Merrimack.

Table 1. Major Tributaries of the Merrimack River Basin.
Tributary Name	Distance from Tributary's Confluence with Main Stem to Ocean	Drainage Area in Square Miles	Percent of Total Basin
Concord River	40	405	8
Nashua River	55	538	11
Souhegan River	63	171	3
Piscataquog River	71	202	4
Suncook River	83	157	3
Soucook River	86 <	77	2
Contoocook River	101	776	15
Winnipesaukee River	115	488	10
Pemigewasset River      Smith River      Baker River      Beebe River      Mad River      East Branch	115	1021	20

Upper, Middle, and Lower River

Another way to describe portions of the Merrimack basin is by separating the watershed into upper, middle, and lower portions. The upper watershed is the portion from Franconia Notch to Manchester, the middle watershed is the portion from Manchester to Nashua, and the lower is the portion from Nashua to where it meets the ocean in Newburyport.
Nearly 80% of the land within ¾ miles of the Upper Merrimack River is currently undeveloped and consists of forest, farm, or wetland. Due in part to its undeveloped nature, the river has a high level of water quality and the ability to support valuable wildlife and plant habitat. Maintenance of this water quality is critical to ensuring the river's future use for water supply and recreational purposes. However, much of the river from Manchester, NH downstream struggles with water quality as a direct result of development, an increase in impervious surfaces (ground cover in which water cannot pass through, such as asphalt), and combined sewer overflows (CSOs). A CSO is sewers system in which stormwater and sewage collect in the same pipe and may be discharged untreated, directly to the river during rain or snowmelt. Impervious surface directly influences the river by dramatically increasing surface runoff (the rate at which water flows across land) that degrades water quality, influences water flow (e.g., flooding and drought), and impacts ecology.

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