Instream Flow
Ensuring that New Hampshire’s 19 designated rivers have enough water for both people and aquatic life.
The Instream Flow Program ensures that rivers continue to flow in spite of the uses and stresses that people put on them. Under natural conditions, rivers flow freely with source waters coming from precipitation via lakes, ponds, wetlands, small streams and groundwater. Under human influences, however, river dynamics can change drastically. People frequently withdraw large amounts of water for drinking and irrigation directly from rivers, as well as from the sources that supply the rivers, particularly lakes and groundwater. Land use changes can result in faster runoff and changes to the stream structure. Many rivers have dams that restrict the amount and timing of water flowing downstream. In addition, the loss of wetlands to land development reduces the amount of water that would normally augment rivers during dry periods. These changes in stream flow can impair river habitat. The Instream Flow Program operates within the New Hampshire Rivers Management and Protection Program statute, Section 9-c (RSA 483:9-c) and in accordance with Administrative Rule Env-Wq 1900.
The program determines the seasonal flows necessary to support both natural aquatic habitats and human uses and then works with water users and dam owners to ensure that their water needs are met while maintaining the protected flows during periods of unusually low flow, even during droughts. The program annually performs a wide range of field activities to collect the environmental data necessary to develop protected instream flow values and evaluate the success of instream flow management; the program’s 2023 Work Plan summarizes those field activities.
Currently, two rivers, the Lamprey and Souhegan Rivers, are actively managed under the Instream Flow Program. In addition, protected instream flows have been established for the Cold River and are being developed for the Ashuelot and Warner Rivers.
Protected Instream Flow Studies & Plans In Progress
The protected instream flow study of the Ashuelot River is underway, the study of the Warner River has been completed, and the draft Protected Instream Flow Study Report for the Cold River has been published and the criteria have been established as water quality criteria. Protected instream flows are criteria that define a stream flow pattern and maintain water for instream public uses and aquatic wildlife, and meet water quality standards. A public hearing on the draft protected instream flows for each river will be scheduled when its draft Protected Instream Flow Study Report is published. NHDES is also working with water users and dam owners along these rivers to determine water use needs and current practices to develop Water Management Plans that balance human needs with the needs of aquatic life identified by each protected instream flow study. A public hearing on each draft Water Management Plan will be scheduled when they are completed.
Real-Time Data
Related Content
- Ashuelot River Study
- Cold River Study
- Isinglass River Study
- Pemigewasset River Study
- Warner River Study
Ashuelot River Study
The protected instream flow study of the Ashuelot River began in 2021. The draft protected instream flows are estimated to be ready for public review and release late in 2023 and the draft Water Management Plan for the Ashuelot River will be developed thereafter.
Real Time Water Data
Cold River Study
The protected instream flow study of the Cold River began in 2019. The final Protected Instream Flow Study Report – Cold River is now available. On January 25, 2022, NHDES’ Commissioner established the protected instream flow values included in the final report as water quality standards, in accordance with Administrative Rule Env-Wq 1904. The draft Water Management Plan for the Cold River is being prepared, with public review and release planned for 2023. Informational sessions are planned for Spring and Summer 2023 to present the plan to all interested individuals. Please watch this space for notifications.
Current Cold River Instream Flow Conditions
Real Time Water Data
Isinglass River Study
The protected instream flow study of the Isinglass River will begin in Spring 2023. The draft Protected Instream Flow Study Report -- Isinglass River is anticipated to be ready for public review in 2025 and the draft Water Management Plan for the Isinglass River will be developed thereafter.
Real Time Water Data
Pemigewasset River Study
The protected instream flow study of the Pemigewasset River will begin in Summer 2023. The draft Protected Instream Flow Study Report- Pemigewasset River is estimated to be ready for public review in 2026. After that, the draft Water Management Plan for the Pemigewasset River will be developed.
Real Time Water Data
Warner River Study
The protected instream flow study of the Warner River began in 2020 and the draft Warner River PISF Study Report is available for public review. An Informational Session about the draft PISF Study Report was held on Tuesday, January 24, at the Warner Town Hall. A public hearing to receive public comments on the draft PISF Study Report will be held on Thursday, February 23, at 7 PM at the Warner Town Hall.
Real Time Water Data
Protected Instream Flow Values Established – Flow Management Underway
The instream flow pilot study was completed in 2015 on the Lamprey and Souhegan rivers. The Report of the Instream Flow Pilot Program summarizes how the protected instream flows and water management plans were developed for each river, and makes recommendations for applying instream flow management on other New Hampshire rivers designated under the Rivers Management and Protection Program.
Lamprey River Protected Instream Flow
The lower Lamprey River, designated in 1990, was the subject of a Protected Instream Flow Study between 2005 and 2009. The upper Lamprey River and five tributaries were added to the Lamprey River designation in 2011, following the protected instream flow study. Protected instream flow criteria for the lower Lamprey River were accepted in 2013. The Lamprey River Water Management Plan was completed in 2013, and applies to only the lower Lamprey River. NHDES began collecting streamflow data from five designated tributaries (Little, North, North Branch, Pawtuckaway, and Piscassic Rivers) in the watershed in June 2022, to support a future Protected Instream Flow Study of these designated rivers, as well as the designated upper Lamprey River. Following the Study, the Lamprey River Water Management Plan will be updated to include the entire designated Lamprey River and its designated tributaries.
Current Lamprey River Instream Flow Conditions
Real Time Water Data
Souhegan River Protected Instream Flow
The upper and lower reaches of the Souhegan River, designated in 2000 were the subject of a Protected Instream Flow Study between 2005 and 2008. Protected instream flow criteria for the upper and lower reaches of the Souhegan River were accepted in 2008, and slightly modified in 2013. The Souhegan River Water Management Plan was completed in 2013.
Current Upper Souhegan River Instream Flow Conditions
Current Lower Souhegan River Instream Flow Conditions
Real Time Water Data
Future River Studies
Prioritization Ranking
In January 2023, following a series of meetings and public hearings, NHDES determined the Isinglass and Pemigewasset Rivers are the next designated rivers on which to conduct a protected instream flow studies. The 2022 Priority List is available for review. Please contact us if you have questions or comments regarding priority rivers for instream flow protection.
Real-time Streamflow Studies
In order to obtain streamflow data to support future management of the designated Ammonoosuc, Contoocook, Exeter, Lamprey, and Piscataquog Rivers, the Instream Flow Program has installed eleven near real-time water level stations along these designated rivers. To view the last 30 days of data from these stations, please use the following link to the NH Hydrologic Data WebMap. In order to view the streamflow stations data, open the Data Layer list, check the boxes to display the NHDES Streamflow Stations and NH Designated Rivers layers (feel free to hide other layers if it makes the map easier to read), and finally close the list by clicking on the X in the upper right corner. Clicking on a streamflow station icon opens its pop-up, where you can see details about the station, a photograph of the station, and follow a link to a dashboard that displays near real-time station data.
Target Fish Communities
A goal of the Instream Flow Program is to ensure that flows in each river are suitable for the fish that should live in that river. Therefore, there is a target fish community report for each river. The target fish community reports include the fish species population distributions that should be found in each designated river.
Estimating Historical Stream Flows
The Instream Flow Program requires at least 30 years of historical stream flow data, but this is not available for every river. Flows can be estimated by comparing nearby gaged rivers and adjusting for watershed area and geography.
Need more information?
Need more information?
All of the New Hampshire Instream Flow Program documents available online can be found here. If you still do not see what you are searching for, contact us for more information.