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United States Office of Water EPA-822-R-08-024 Environmental Protection Office of Science and Technology December 2008 Agency Washington, DC 20460 www.epa.gov METHODS FOR EVALUATING WETLAND CONDITION #20 Wetland Hydrology United States Office of Water EPA-822-R-08-024 Environmental Protection Office of Science and Technolog December 2008 Agency Washington, DC 20460 www.epa.gov METHODS FOR EVALUATING WETLAND CONDITION #20 Wetland Hydrology Principal Contributor University of Georgia Todd Rasmussen Prepared jointly by: The U.S. Environmental Protection Agency Health and Ecological Criteria Division (Office of Science and Technology) and Wetlands Division (Office of Wetlands, Oceans, and Watersheds) Notice The material in this document has been subjected to U.S. Environmental Protection Agency (EPA) technical review and has been approved for publication as an EPA document. The information contained herein is offered to the reader as a review of the “state of the science” concerning wetland bioassessment and nutrient enrichment and is not intended to be prescriptive guidance or firm advice. Mention of trade names, products or services does not convey, and should not be interpreted as conveying official EPA approval, endorsement, or recommendation. Appropriate Citation U.S. EPA. 2008. Methods for Evaluating Wetland Condition: Wetland Hydrology. Office of Water, U.S. Environmental Protection Agency, Washington, DC. EPA-822-R-08-024. Acknowledgements EPA acknowledges the contribution of Todd Rasmussen of the University of Georgia for writing of this module. This entire document can be downloaded from the following U.S. EPA websites: http://www.epa.gov/waterscience/criteria/wetlands/ http://www.epa.gov/owow/wetlands/bawwg/publicat.html ii CONTENTS FORE W ORD ������������������������������������������������������������������������������������������������������������ VI LIST OF “METHODS FOR EVALUATING WETLAND CONDITION ” MODULES VI I WETLAND HYDROLOGY 1 INTRODU C TION �������������������������������������������������������������������������������������������������������� 1 HYDROLOGI C MEASURES ���������������������������������������������������������������������������������������� 2 WETLAND WATER BUDGETS �������������������������������������������������������������������������������� 11 WATER BUDGET CO M PONENTS 14 OPEN CHANNEL MEASURE M ENTS ������������������������������������������������������������������������23 CONTROL STRU C TURES ��������������������������������������������������������������������������������������24 EVOLUTION AND ALTERATION OF WETLAND HYDROLOGY ��������������������������������������29 REFEREN C ES ��������������������������������������������������������������������������������������������������������35 LIST OF TA B LES TA B LE 1A: TIDAL W ETLAND TYPES 3 TA B LE 1B: NON -TIDAL W ETLAND TYPES . .4 TA B LE 2: ILLUSTRATIVE W ATER B UDGET C O M PONENTS (mm /YEAR ) FOR SELE C TED W ETLAND TYPES . 16 TA B LE 3: TYPES OF CHANNEL CONTROL STRU C TURES 25 TA B LE 4: TW O GENERAL TYPES OF WEIRS 26 iii LIST OF FIGURES FIGURE 1: MULTIPLE STAFF GAGES C AN B E USED TO DETER M INE W ETLAND W ATER LEVELS FOR A W ETLAND W ITH HIGHLY VARIA B LE STAGES THE HIGHER GAGE IS USED DURING W ET PERIODS AND IS EASIER TO READ THAN THE M ORE DISTANT ONE ON C E W ATER LEVELS FALL B ELO W THE HIGHER GAGE , THEN THE LO W ER GAGE IS USED 5 FIGURE 2: PIEZO M ETERS ARE USED TO M ONITOR W ATER LEVEL C HANGES IN THE SU B SURFA C E MULTIPLE PIEZO M ETERS (C ALLED A NES T ) C AN B E INSTALLED NEXT TO EA C H OTHER , ONE IN EA C H SOIL HORIZON , IF VERTI C AL FLO W B ET W EEN SOIL HORIZONS IS EXPE C TED ADDITIONAL PIEZO M ETERS C AN B E INSTALLED IN THE B EDRO C K IF SU C H M ATERIALS AFFE C T THE HYDROLOGY OF THE W ETLAND . .6 FIGURE 3: TI M E DO M AIN REFLE C TO M ETER PRO B ES C AN B E USED TO M ONITOR SOIL M OISTURE SATURATION OVER TI M E , PROVIDING AN ESTI M ATE OF THE W ATER C HANGE IN THE SU B SURFA C E 6 FIGURE 4: H YDROGRAPH FOR A SHORT PERIOD OF TI M E SHO W ING THE W ATER LEVEL VARIATION NOTE THAT THE HYDROPERIOD IS M ARKED FOR A FE W STAGES . 8 FIGURE 5: LEFT : WETLAND HYDROPERIOD PLOT SHO W ING DURATION OF FLOODING VERSUS STAGE RIGHT : WETLAND STAGE -FREQUEN C Y PLOT SHO W ING NU mb ER OF EX C EEDAN C ES PER YEAR NOTE THAT THE LONGEST DURATION OF FLOODING O cc URS AT THE LO W ER STAGES , AND VI C E VERSA LO W ER STAGES HAVE A HIGHER FREQUEN C Y OF B EING FLOODED THAN HIGHER STAGES . 8 FIGURE 6: WETLAND STAGE -FREQUEN C Y -DURATION PLOT SHO W ING DURATION OF FLOODING VERSUS STAGE FOR A RANGE OF FREQUEN C IES . .9 FIGURE 7: STAGE -AREA (TOP ) AND STAGE -VOLU M E (B OTTO M ) C URVES SHO W ING C HANGES IN W ETLAND AREA AND VOLU M E AS A FUN C TION OF STAGE FLOODED W ETLAND AREA IS ZERO ON C E W ATER STAGE DROPS B ELO W THE GROUND SURFA C E IN THE DEEPEST SE C TION OF THE W ETLAND VOLU M E OF W ATER STORAGE IS NOT ZERO B E C AUSE THE B ED SEDI M ENTS M AY B E A B LE TO STORE AND RELEASE W ATER WETLAND AREA ALSO IN C REASES RAPIDLY IF A LEVEE IS OVERTOPPED 13 iv LIST OF FIGURES (C ONTINUED ) FIGURE 8: RELATIONSHIP B ET W EEN HYDROLOGI C EX C HANGES AND NONTIDAL W ETLAND TYPES . .15 FIGURE 9: EFFE C T OF W ETLANDS ON SURFI C IAL AQUIFER M OVE M ENT INFLO W TO W ETLAND IS ON SIDE W HERE W ATER TA B LE LEVELS ARE HIGHER THAN W ETLAND OUTFLO W IS ON SIDE W HERE W ATER TA B LES ARE LO W ER . .19 FIGURE 10: NET W ORK OF PIEZO M ETERS REQUIRED TO M AP W ATER LEVELS IN THE VI C INITY OF A W ETLAND NOTE THAT THE W ATER LEVEL C ONTOURS C AN B E M ADE B ASED UPON INTERPOLATION B ET W EEN M EASURE M ENTS W ITHIN INDIVIDUAL PIEZO M ETERS 21 FIGURE 11: WATER LEVEL B EHAVIOR SHO W ING SLO W DE C LINE IN B ASEFLO W ALONG W ITH A DIS C RETE STOR M EVENT W ITH ITS ASSO C IATED STOR M FLO W 22 FIGURE 12: RATING C URVE SHO W ING RELATIONSHIP B ET W EEN W ATER LEVEL STAGE AND STREA M DIS C HARGE NOTE C HANGE IN SLOPE I N RELATIONSHIP AS DIFFERENT PARTS OF THE C HANNEL ARE W ETTED AS THE STAGE C HANGES . 23 FIGURE 13: THREE TYPES OF W EIRS (RE C TANGULAR , TRIANGULAR , TRAPEZOIDAL , FLOODED ORIFI C E ) USED AS C ONTROL STRU C TURES FOR M EASURING STREA M DIS C HARGE WATER LEVEL (STAGE ) IS M EASURED IN W EIR B ASIN UPSTREA M OF W EIR B LADE 26 v FORE W ORD In 1999, the U.S. Environmental Protection Agency (EPA) began work on this series of reports entitled Methods for Evaluating Wetland Condition. The purpose of these reports is to help States and Tribes develop methods to evaluate (1) the overall ecological condition of wetlands using biological assessments and (2) nutrient enrichment of wetlands, which is one of the pri- mary stressors damaging wetlands in many parts of the country. This information is intended to serve as a starting point for States and Tribes to eventually establish biological and nutrient water quality criteria specifically refined for wetland waterbodies. This purpose was to be accomplished by providing a series of “state of the science” modules concerning wetland bioassessment as well as the nutrient enrichment of wetlands. The individual module format was used instead of one large publication to facilitate the addition of other reports as wetland science progresses and wetlands are further incorporated into water quality programs. Also, this modular approach allows EPA to revise reports without having to reprint them all. A list of the inaugural set of 20 modules can be found at the end of this section. This last set of reports is the product of a collaborative effort between EPA’s Health and Ecological Criteria Division of the Office of Science and Technology (OST) and the Wetlands Division of the Office of Wetlands, Oceans and Watersheds (OWOW). The reports were initiated with the support and oversight of Thomas J. Danielson then of OWOW, Amanda K. Parker and Susan K. Jackson (OST), and seen to completion by Ifeyinwa F. Davis (OST). EPA relied on the input and expertise of the contributing authors to publish the remaining modules. More information about biological and nutrient criteria is available at the following EPA website: http://www.epa.gov/ost/standards More information about wetland biological assessments is available at the following EPA website: http://www.epa.gov/owow/wetlands/bawwg vi LIST Of “METHODS FOR EValUATING WETlanD CONDITION” MODULES MODULE # MODULE TITLE 1 ................. INTRODU C TION TO WETLAND BIOLOGIC AL ASSESS M ENT 2 ................. INTRODU C TION TO WETLAND NUTRIENT ASSESS M ENT 3 ................. THE STATE OF WETLAND SC IEN C E 4 ................. STUDY DESIGN FOR MONITORING WETLANDS 5 ................. AD M INISTRATIVE FRA M E W ORK FOR THE IM PLE M ENTATION OF A WETLAND BIOASSESS M ENT PROGRA M 6 ................. DEVELOPING METRI C S AND INDEXES OF BIOLOGIC AL INTEGRITY 7 ................. WETLANDS CLASSIFIC AT ION 8 ................. VOLUNTEERS AND WETLAND BIO M ONITORING 9 ................. DEVELOPING AN INVERTE B RATE INDEX OF BIOLOGIC AL INTEGRITY FOR WETLANDS 10 ............... USING VEGETATION TO ASSESS ENVIRON M ENTAL CONDITIONS IN WETLANDS 11 ............... USING ALGAE TO ASSESS ENVIRON M ENTAL CONDITIONS IN WETLANDS 12 ............... USING A M PHI B IANS IN BIOASSESS M ENTS OF WETLANDS 13 ............... BIOLOGIC AL ASSESS M ENT METHODS FOR BIRDS 14 ..............