The Hydrology of the Mora Watershed

Ruji Rajbhandari

GIS in Water Resources Engineering

Spring 2008

Introduction:

Mora watershed is located in New Mexico mainly within Mora County and touches Colfax and San Miguel County. Mora valley and La Cueva are located in Mora County. Mora valley is located between Las Vegas and Taos. It is a Hispanic settlement and a farming community. The lands were given as land grant to old settlers of Mora. Farming and construction are the major sources of income. Acequia system is still prevalent in this part of New Mexico. Acequias are the main source of irrigation and they have active Acequia association. Mora River from Mora Watershed flows through the valley towards east.

Mora watershed covers an area of about 1456 sq. miles. It is located in Arkansas White Red watershed region. This region touches eight states in U.S. i.e. States of Arkansas, Colorado, Kansas, Missouri, New Mexico, Texas and Louisiana, and the State of Oklahoma entirely. Mora watershed lies in Hydrologic Unit Code 11080004.

The geographic location of water shed is West: -105.5 ⁰ East: -104.3 ⁰

North: 36.36⁰ South: 35.5 ⁰

Objectives:

The main objective of this project is to map and delineate the Mora watershed to analyze precipitation and stream flow data for a period of 1970 to 2000. Using GIS maps is the main objective and data from Mora River at La Cueva and areas around Mora valley will be used for analysis.

Data Collection:

Data Source:

The main sources of my data are from USGS website and RGIS website. Different shape files like road, boundary, stream, cities, etc were downloaded from RGIS website. I have also used USGS gage data for Mora River at La Cueva and stream flow data from USGS website. The DEM file for Mora watershed was collected from RGIS website where I collected 17 DEM files.

The precipitation and snow fall data were from Natural Resources Conservation Service website for Gascon, NM. My initial aim was to collect data for Rio La Casa, Mora but I was unable to find data related to that water gage location so I choose La Cueva.

I have used NAD 1983 as my projection system because most of the files I found were in this coordinate system and it was convenient using the coordinate that have been mostly used. The software environment I used was Arc Info, where I used extensions like Spatial Analyst for doing Hydrologic modeling.

www.rgis.unm.edu – RGIS website

www.water.usgs.gov- USGS website for stream flow

http://www.wcc.nrcs.usda.gov/climate/prism.html - NRCS website

Base Map Creation:

The first step in map creation was to create a base map of Mora watershed using boundary, river networks and added USGS water gage sites. The USGS gage locations were imported into excel, changed to decimal degrees and then projected into map by converting to X-Y data.

The Mora River runs through the middle of the watershed towards East. On the map we can see the location of USGS water gage sites and dams. The map shows how the tributaries are flowing towards the central main river and flowing towards east.

Hydrologic Modeling:

Hydrologic modeling was the toughest part of my project. I collected 17 DEM files from RGIS website and mosaic them together. At first I tried to use DEM file covering the northern portion of New Mexico which I found in RGIS. But the file was too large and it too hours processing one command. So I had to search each DEM file that was located in my watershed boundary.

I performed the steps as we learned from our assignment 4. I Mosaic all the 17 files using Raster Calculator in Spatial Analyst extension and filled the pits on the DEM file to avoid discontinuous streams. The elevation ranged from 1330m to 3930m. Then I followed a series of steps to model the watershed. The steps I followed are shown on the flow diagram.

Flow chart showing steps in Hydrologic Modeling.

Flow direction and flow accumulation in the watershed can be seen on the watershed delineated map.

The relation between the altitude and stream networks can be clearly seen on map on Appendix 4. It shows the flow of water from all the tributaries towards the central river and then flowing towards east direction.

Data Analysis:

The Stream flow, precipitation and snow fall data were plotted in Excel graph. I used average monthly snowfall data and average monthly precipitation data. For Stream flow I used average of monthly mean data. I created comparison graphs for stream flow and precipitation and stream flow and snow fall. The stream flow data was collected at Mora River at la Cueva for years 1970 to 2000. The graphs are shown below.

Detail Map showing water gage sites in Mora Valley

From the graph we can see the comparison between precipitation and stream flow. The prominent characters in this graph are during the month of July, August, September or monsoon months the stream flow is the highest.

Whereas in the graph below during summer months of April, May and June when the snow melts stream flow is the highest. So we can conclude that the stream flow in the Mora River is high during summer due to snow melt from the mountains and then during monsoon season due to precipitation and runoff from the watershed.

Future Work:

Due to time constraints and availability of Mora County I was not able to get the details that I was expecting to get. For future work detail analysis using weather and snow data will be helpful. Getting weather data from PRISM website and analyzing might give more extensive results.